Apache Ignite 2.4 release

[Ivan Rakov]

> Why create a new term to define something that has already been defined?
That makes sense. I'm ok with FSYNC.
Anton, I don't understand why we should rename LOG_ONLY to SYNC. We started this discussion with bad naming of DEFAULT, but this has nothing to do with LOG_ONLY (even though it may be scientific - but SYNC sounds scientific as well).

Best Regards,
Ivan Rakov

On 16.02.2018 15:55, Anton Vinogradov wrote:

>   >> I had idea to name old default as FSYNC, but it would be too scientific.
> So, then it can be  FSYNC, SYNC, BACKGROUND and NONE!
>
> On Fri, Feb 16, 2018 at 3:49 PM, Dmitriy Setrakyan <[hidden email]>
> wrote:
>
>> On Fri, Feb 16, 2018 at 6:26 AM, Dmitry Pavlov <[hidden email]>
>> wrote:
>>
>>> I had idea to name old default as FSYNC, but it would be too scientific.
>>>
>> I like FSYNC, I do not think it is too scientific. Definitely not more
>> scientific than LOG_ONLY.
>>
>> For old DEFAULT, STRICT or STRICT_SYNC - IMO are best options, so I agree
>>> with Ivan.
>>>
>> Not sure I like STRICT. In Linux world, fsync is a well known command which
>> does exactly what our FSYNC mode will do:
>> http://man7.org/linux/man-pages/man2/fsync.2.html . STRICT, on the other
>> hand, is not a commonly understood term. Why create a new term to define
>> something that has already been defined?
>>
>> Also, what if tomorrow we need to add an even stricter parameter? Then we
>> are back to the same problem we are trying to fix right now.
>>
>> D.
>>

[dsetrakyan]

On Fri, Feb 16, 2018 at 7:02 AM, Ivan Rakov <[hidden email]> wrote:

> Why create a new term to define something that has already been defined?
>>
> That makes sense. I'm ok with FSYNC.
> Anton, I don't understand why we should rename LOG_ONLY to SYNC. We
> started this discussion with bad naming of DEFAULT, but this has nothing to
> do with LOG_ONLY (even though it may be scientific - but SYNC sounds
> scientific as well).
>

I agree with Ivan, we should not go wild with renaming. However, I would
like to find out what is the meaning behind the LOG_ONLY name. Can someone
explain?

D.

[Ilya Lantukh]

I am OK with either FSYNC or STRICT variant.

LOG_ONLY name means "log without fsync".

On Fri, Feb 16, 2018 at 4:05 PM, Dmitriy Setrakyan <[hidden email]>
wrote:

> On Fri, Feb 16, 2018 at 7:02 AM, Ivan Rakov <[hidden email]> wrote:
>
> > Why create a new term to define something that has already been defined?
> >>
> > That makes sense. I'm ok with FSYNC.
> > Anton, I don't understand why we should rename LOG_ONLY to SYNC. We
> > started this discussion with bad naming of DEFAULT, but this has nothing
> to
> > do with LOG_ONLY (even though it may be scientific - but SYNC sounds
> > scientific as well).
> >
>
> I agree with Ivan, we should not go wild with renaming. However, I would
> like to find out what is the meaning behind the LOG_ONLY name. Can someone
> explain?
>
> D.
>

--
Best regards,
Ilya

[Anton Vinogradov]

Log only mode: flushes application buffers.
So, in synced mode without fsync guarantee. That's why I propose to rename
it as SYNC.

On Fri, Feb 16, 2018 at 4:49 PM, Ilya Lantukh <[hidden email]> wrote:

> I am OK with either FSYNC or STRICT variant.
>
> LOG_ONLY name means "log without fsync".
>
> On Fri, Feb 16, 2018 at 4:05 PM, Dmitriy Setrakyan <[hidden email]>
> wrote:
>
> > On Fri, Feb 16, 2018 at 7:02 AM, Ivan Rakov <[hidden email]>
> wrote:
> >
> > > Why create a new term to define something that has already been
> defined?
> > >>
> > > That makes sense. I'm ok with FSYNC.
> > > Anton, I don't understand why we should rename LOG_ONLY to SYNC. We
> > > started this discussion with bad naming of DEFAULT, but this has
> nothing
> > to
> > > do with LOG_ONLY (even though it may be scientific - but SYNC sounds
> > > scientific as well).
> > >
> >
> > I agree with Ivan, we should not go wild with renaming. However, I would
> > like to find out what is the meaning behind the LOG_ONLY name. Can
> someone
> > explain?
> >
> > D.
> >
>
>
>
> --
> Best regards,
> Ilya
>

[dsetrakyan]

Igniters, just to clarify, does the term LOG_ONLY mean anything in the
industry or is this just an Ignite term?

D.

On Fri, Feb 16, 2018 at 8:03 AM, Anton Vinogradov <[hidden email]>
wrote:

> Log only mode: flushes application buffers.
> So, in synced mode without fsync guarantee. That's why I propose to rename
> it as SYNC.
>
> On Fri, Feb 16, 2018 at 4:49 PM, Ilya Lantukh <[hidden email]>
> wrote:
>
> > I am OK with either FSYNC or STRICT variant.
> >
> > LOG_ONLY name means "log without fsync".
> >
> > On Fri, Feb 16, 2018 at 4:05 PM, Dmitriy Setrakyan <
> [hidden email]>
> > wrote:
> >
> > > On Fri, Feb 16, 2018 at 7:02 AM, Ivan Rakov <[hidden email]>
> > wrote:
> > >
> > > > Why create a new term to define something that has already been
> > defined?
> > > >>
> > > > That makes sense. I'm ok with FSYNC.
> > > > Anton, I don't understand why we should rename LOG_ONLY to SYNC. We
> > > > started this discussion with bad naming of DEFAULT, but this has
> > nothing
> > > to
> > > > do with LOG_ONLY (even though it may be scientific - but SYNC sounds
> > > > scientific as well).
> > > >
> > >
> > > I agree with Ivan, we should not go wild with renaming. However, I
> would
> > > like to find out what is the meaning behind the LOG_ONLY name. Can
> > someone
> > > explain?
> > >
> > > D.
> > >
> >
> >
> >
> > --
> > Best regards,
> > Ilya
> >
>

[Ivan Rakov]

Looks like it's an Ignite term - I've never heard of it outside Ignite
scope.

Though, renaming existing enum value requires keeping old as deprecated.
DEFAULT is confusing enough to pay this price.
As for LOG_ONLY, I think we can keep it as long as it has good and
definitive javadoc.

Best Regards,
Ivan Rakov

On 16.02.2018 17:07, Dmitriy Setrakyan wrote:

> Igniters, just to clarify, does the term LOG_ONLY mean anything in the
> industry or is this just an Ignite term?
>
> D.
>
> On Fri, Feb 16, 2018 at 8:03 AM, Anton Vinogradov <[hidden email]>
> wrote:
>
>> Log only mode: flushes application buffers.
>> So, in synced mode without fsync guarantee. That's why I propose to rename
>> it as SYNC.
>>
>> On Fri, Feb 16, 2018 at 4:49 PM, Ilya Lantukh <[hidden email]>
>> wrote:
>>
>>> I am OK with either FSYNC or STRICT variant.
>>>
>>> LOG_ONLY name means "log without fsync".
>>>
>>> On Fri, Feb 16, 2018 at 4:05 PM, Dmitriy Setrakyan <
>> [hidden email]>
>>> wrote:
>>>
>>>> On Fri, Feb 16, 2018 at 7:02 AM, Ivan Rakov <[hidden email]>
>>> wrote:
>>>>> Why create a new term to define something that has already been
>>> defined?
>>>>> That makes sense. I'm ok with FSYNC.
>>>>> Anton, I don't understand why we should rename LOG_ONLY to SYNC. We
>>>>> started this discussion with bad naming of DEFAULT, but this has
>>> nothing
>>>> to
>>>>> do with LOG_ONLY (even though it may be scientific - but SYNC sounds
>>>>> scientific as well).
>>>>>
>>>> I agree with Ivan, we should not go wild with renaming. However, I
>> would
>>>> like to find out what is the meaning behind the LOG_ONLY name. Can
>>> someone
>>>> explain?
>>>>
>>>> D.
>>>>
>>>
>>>
>>> --
>>> Best regards,
>>> Ilya
>>>

[dsetrakyan]

Well, I cannot say that I like the name LOG_ONLY, but I would vote to keep
it for now, given that it is already documented in many places, blogs, and
examples.

D.

On Fri, Feb 16, 2018 at 8:13 AM, Ivan Rakov <[hidden email]> wrote:

> Looks like it's an Ignite term - I've never heard of it outside Ignite
> scope.
>
> Though, renaming existing enum value requires keeping old as deprecated.
> DEFAULT is confusing enough to pay this price.
> As for LOG_ONLY, I think we can keep it as long as it has good and
> definitive javadoc.
>
> Best Regards,
> Ivan Rakov
>
>
> On 16.02.2018 17:07, Dmitriy Setrakyan wrote:
>
>> Igniters, just to clarify, does the term LOG_ONLY mean anything in the
>> industry or is this just an Ignite term?
>>
>> D.
>>
>> On Fri, Feb 16, 2018 at 8:03 AM, Anton Vinogradov <
>> [hidden email]>
>> wrote:
>>
>> Log only mode: flushes application buffers.
>>> So, in synced mode without fsync guarantee. That's why I propose to
>>> rename
>>> it as SYNC.
>>>
>>> On Fri, Feb 16, 2018 at 4:49 PM, Ilya Lantukh <[hidden email]>
>>> wrote:
>>>
>>> I am OK with either FSYNC or STRICT variant.
>>>>
>>>> LOG_ONLY name means "log without fsync".
>>>>
>>>> On Fri, Feb 16, 2018 at 4:05 PM, Dmitriy Setrakyan <
>>>>
>>> [hidden email]>
>>>
>>>> wrote:
>>>>
>>>> On Fri, Feb 16, 2018 at 7:02 AM, Ivan Rakov <[hidden email]>
>>>>>
>>>> wrote:
>>>>
>>>>> Why create a new term to define something that has already been
>>>>>>
>>>>> defined?
>>>>
>>>>> That makes sense. I'm ok with FSYNC.
>>>>>> Anton, I don't understand why we should rename LOG_ONLY to SYNC. We
>>>>>> started this discussion with bad naming of DEFAULT, but this has
>>>>>>
>>>>> nothing
>>>>
>>>>> to
>>>>>
>>>>>> do with LOG_ONLY (even though it may be scientific - but SYNC sounds
>>>>>> scientific as well).
>>>>>>
>>>>>> I agree with Ivan, we should not go wild with renaming. However, I
>>>>>
>>>> would
>>>
>>>> like to find out what is the meaning behind the LOG_ONLY name. Can
>>>>>
>>>> someone
>>>>
>>>>> explain?
>>>>>
>>>>> D.
>>>>>
>>>>>
>>>>
>>>> --
>>>> Best regards,
>>>> Ilya
>>>>
>>>>
>

[Vladimir Ozerov]

Igniters,

Sorry for pouring oil on the flames, but from database perspective moving
from FSYNC to non-FSYNC mode appears to be a mistake. When you work with
database, your main expectation is that it will save your data. All
production database vendor make sure that you are safe, not that you are
fast. Moreover, some vendors even prevent you from being in unsafe mode
(e.g. you cannot disable fsync in SQL Server at all).

If we continue going in this direction, we will end up with a product,
which is unsafe out of the box and require tons of documentation to
understand how to make it safe. Definitely not the right message to the
market. This is like a car without brakes - would you like to drive it? If
this is Need For Speed game and you have unlimited lives (in-memory cache
with backing store), then yes. If this is a real life with (persistence) -
then no.

On Fri, Feb 16, 2018 at 5:20 PM, Dmitriy Setrakyan <[hidden email]>
wrote:

> Well, I cannot say that I like the name LOG_ONLY, but I would vote to keep
> it for now, given that it is already documented in many places, blogs, and
> examples.
>
> D.
>
> On Fri, Feb 16, 2018 at 8:13 AM, Ivan Rakov <[hidden email]> wrote:
>
> > Looks like it's an Ignite term - I've never heard of it outside Ignite
> > scope.
> >
> > Though, renaming existing enum value requires keeping old as deprecated.
> > DEFAULT is confusing enough to pay this price.
> > As for LOG_ONLY, I think we can keep it as long as it has good and
> > definitive javadoc.
> >
> > Best Regards,
> > Ivan Rakov
> >
> >
> > On 16.02.2018 17:07, Dmitriy Setrakyan wrote:
> >
> >> Igniters, just to clarify, does the term LOG_ONLY mean anything in the
> >> industry or is this just an Ignite term?
> >>
> >> D.
> >>
> >> On Fri, Feb 16, 2018 at 8:03 AM, Anton Vinogradov <
> >> [hidden email]>
> >> wrote:
> >>
> >> Log only mode: flushes application buffers.
> >>> So, in synced mode without fsync guarantee. That's why I propose to
> >>> rename
> >>> it as SYNC.
> >>>
> >>> On Fri, Feb 16, 2018 at 4:49 PM, Ilya Lantukh <[hidden email]>
> >>> wrote:
> >>>
> >>> I am OK with either FSYNC or STRICT variant.
> >>>>
> >>>> LOG_ONLY name means "log without fsync".
> >>>>
> >>>> On Fri, Feb 16, 2018 at 4:05 PM, Dmitriy Setrakyan <
> >>>>
> >>> [hidden email]>
> >>>
> >>>> wrote:
> >>>>
> >>>> On Fri, Feb 16, 2018 at 7:02 AM, Ivan Rakov <[hidden email]>
> >>>>>
> >>>> wrote:
> >>>>
> >>>>> Why create a new term to define something that has already been
> >>>>>>
> >>>>> defined?
> >>>>
> >>>>> That makes sense. I'm ok with FSYNC.
> >>>>>> Anton, I don't understand why we should rename LOG_ONLY to SYNC. We
> >>>>>> started this discussion with bad naming of DEFAULT, but this has
> >>>>>>
> >>>>> nothing
> >>>>
> >>>>> to
> >>>>>
> >>>>>> do with LOG_ONLY (even though it may be scientific - but SYNC sounds
> >>>>>> scientific as well).
> >>>>>>
> >>>>>> I agree with Ivan, we should not go wild with renaming. However, I
> >>>>>
> >>>> would
> >>>
> >>>> like to find out what is the meaning behind the LOG_ONLY name. Can
> >>>>>
> >>>> someone
> >>>>
> >>>>> explain?
> >>>>>
> >>>>> D.
> >>>>>
> >>>>>
> >>>>
> >>>> --
> >>>> Best regards,
> >>>> Ilya
> >>>>
> >>>>
> >
>

[Dmitriy Pavlov]

Hi Vladimir,

What you saying is defenetely make sence.

In the same time LOG_ONLY is also safe mode, user will be able to restore
system after crash. If it is not true, we should create critical ticket and
fix it.

Do you know other databases defaults, such as Cassandra, Oracle, Postgre?

Sincerely,
Dmitriy Pavlov

пт, 16 февр. 2018 г. в 18:41, Vladimir Ozerov <[hidden email]>:

> Igniters,
>
> Sorry for pouring oil on the flames, but from database perspective moving
> from FSYNC to non-FSYNC mode appears to be a mistake. When you work with
> database, your main expectation is that it will save your data. All
> production database vendor make sure that you are safe, not that you are
> fast. Moreover, some vendors even prevent you from being in unsafe mode
> (e.g. you cannot disable fsync in SQL Server at all).
>
> If we continue going in this direction, we will end up with a product,
> which is unsafe out of the box and require tons of documentation to
> understand how to make it safe. Definitely not the right message to the
> market. This is like a car without brakes - would you like to drive it? If
> this is Need For Speed game and you have unlimited lives (in-memory cache
> with backing store), then yes. If this is a real life with (persistence) -
> then no.
>
> On Fri, Feb 16, 2018 at 5:20 PM, Dmitriy Setrakyan <[hidden email]>
> wrote:
>
> > Well, I cannot say that I like the name LOG_ONLY, but I would vote to
> keep
> > it for now, given that it is already documented in many places, blogs,
> and
> > examples.
> >
> > D.
> >
> > On Fri, Feb 16, 2018 at 8:13 AM, Ivan Rakov <[hidden email]>
> wrote:
> >
> > > Looks like it's an Ignite term - I've never heard of it outside Ignite
> > > scope.
> > >
> > > Though, renaming existing enum value requires keeping old as
> deprecated.
> > > DEFAULT is confusing enough to pay this price.
> > > As for LOG_ONLY, I think we can keep it as long as it has good and
> > > definitive javadoc.
> > >
> > > Best Regards,
> > > Ivan Rakov
> > >
> > >
> > > On 16.02.2018 17:07, Dmitriy Setrakyan wrote:
> > >
> > >> Igniters, just to clarify, does the term LOG_ONLY mean anything in the
> > >> industry or is this just an Ignite term?
> > >>
> > >> D.
> > >>
> > >> On Fri, Feb 16, 2018 at 8:03 AM, Anton Vinogradov <
> > >> [hidden email]>
> > >> wrote:
> > >>
> > >> Log only mode: flushes application buffers.
> > >>> So, in synced mode without fsync guarantee. That's why I propose to
> > >>> rename
> > >>> it as SYNC.
> > >>>
> > >>> On Fri, Feb 16, 2018 at 4:49 PM, Ilya Lantukh <[hidden email]
> >
> > >>> wrote:
> > >>>
> > >>> I am OK with either FSYNC or STRICT variant.
> > >>>>
> > >>>> LOG_ONLY name means "log without fsync".
> > >>>>
> > >>>> On Fri, Feb 16, 2018 at 4:05 PM, Dmitriy Setrakyan <
> > >>>>
> > >>> [hidden email]>
> > >>>
> > >>>> wrote:
> > >>>>
> > >>>> On Fri, Feb 16, 2018 at 7:02 AM, Ivan Rakov <[hidden email]>
> > >>>>>
> > >>>> wrote:
> > >>>>
> > >>>>> Why create a new term to define something that has already been
> > >>>>>>
> > >>>>> defined?
> > >>>>
> > >>>>> That makes sense. I'm ok with FSYNC.
> > >>>>>> Anton, I don't understand why we should rename LOG_ONLY to SYNC.
> We
> > >>>>>> started this discussion with bad naming of DEFAULT, but this has
> > >>>>>>
> > >>>>> nothing
> > >>>>
> > >>>>> to
> > >>>>>
> > >>>>>> do with LOG_ONLY (even though it may be scientific - but SYNC
> sounds
> > >>>>>> scientific as well).
> > >>>>>>
> > >>>>>> I agree with Ivan, we should not go wild with renaming. However, I
> > >>>>>
> > >>>> would
> > >>>
> > >>>> like to find out what is the meaning behind the LOG_ONLY name. Can
> > >>>>>
> > >>>> someone
> > >>>>
> > >>>>> explain?
> > >>>>>
> > >>>>> D.
> > >>>>>
> > >>>>>
> > >>>>
> > >>>> --
> > >>>> Best regards,
> > >>>> Ilya
> > >>>>
> > >>>>
> > >
> >
>

[Vladimir Ozerov]

Log only mode is not safe - data might be corrupted in case of system
crash. Oracle - fsync, Postgres - fsync, SQL Server - fsync, Cassandra -
similar to our “background”.

пт, 16 февр. 2018 г. в 19:11, Dmitry Pavlov <[hidden email]>:

> Hi Vladimir,
>
> What you saying is defenetely make sence.
>
> In the same time LOG_ONLY is also safe mode, user will be able to restore
> system after crash. If it is not true, we should create critical ticket and
> fix it.
>
> Do you know other databases defaults, such as Cassandra, Oracle, Postgre?
>
> Sincerely,
> Dmitriy Pavlov
>
> пт, 16 февр. 2018 г. в 18:41, Vladimir Ozerov <[hidden email]>:
>
> > Igniters,
> >
> > Sorry for pouring oil on the flames, but from database perspective moving
> > from FSYNC to non-FSYNC mode appears to be a mistake. When you work with
> > database, your main expectation is that it will save your data. All
> > production database vendor make sure that you are safe, not that you are
> > fast. Moreover, some vendors even prevent you from being in unsafe mode
> > (e.g. you cannot disable fsync in SQL Server at all).
> >
> > If we continue going in this direction, we will end up with a product,
> > which is unsafe out of the box and require tons of documentation to
> > understand how to make it safe. Definitely not the right message to the
> > market. This is like a car without brakes - would you like to drive it?
> If
> > this is Need For Speed game and you have unlimited lives (in-memory cache
> > with backing store), then yes. If this is a real life with (persistence)
> -
> > then no.
> >
> > On Fri, Feb 16, 2018 at 5:20 PM, Dmitriy Setrakyan <
> [hidden email]>
> > wrote:
> >
> > > Well, I cannot say that I like the name LOG_ONLY, but I would vote to
> > keep
> > > it for now, given that it is already documented in many places, blogs,
> > and
> > > examples.
> > >
> > > D.
> > >
> > > On Fri, Feb 16, 2018 at 8:13 AM, Ivan Rakov <[hidden email]>
> > wrote:
> > >
> > > > Looks like it's an Ignite term - I've never heard of it outside
> Ignite
> > > > scope.
> > > >
> > > > Though, renaming existing enum value requires keeping old as
> > deprecated.
> > > > DEFAULT is confusing enough to pay this price.
> > > > As for LOG_ONLY, I think we can keep it as long as it has good and
> > > > definitive javadoc.
> > > >
> > > > Best Regards,
> > > > Ivan Rakov
> > > >
> > > >
> > > > On 16.02.2018 17:07, Dmitriy Setrakyan wrote:
> > > >
> > > >> Igniters, just to clarify, does the term LOG_ONLY mean anything in
> the
> > > >> industry or is this just an Ignite term?
> > > >>
> > > >> D.
> > > >>
> > > >> On Fri, Feb 16, 2018 at 8:03 AM, Anton Vinogradov <
> > > >> [hidden email]>
> > > >> wrote:
> > > >>
> > > >> Log only mode: flushes application buffers.
> > > >>> So, in synced mode without fsync guarantee. That's why I propose to
> > > >>> rename
> > > >>> it as SYNC.
> > > >>>
> > > >>> On Fri, Feb 16, 2018 at 4:49 PM, Ilya Lantukh <
> [hidden email]
> > >
> > > >>> wrote:
> > > >>>
> > > >>> I am OK with either FSYNC or STRICT variant.
> > > >>>>
> > > >>>> LOG_ONLY name means "log without fsync".
> > > >>>>
> > > >>>> On Fri, Feb 16, 2018 at 4:05 PM, Dmitriy Setrakyan <
> > > >>>>
> > > >>> [hidden email]>
> > > >>>
> > > >>>> wrote:
> > > >>>>
> > > >>>> On Fri, Feb 16, 2018 at 7:02 AM, Ivan Rakov <
> [hidden email]>
> > > >>>>>
> > > >>>> wrote:
> > > >>>>
> > > >>>>> Why create a new term to define something that has already been
> > > >>>>>>
> > > >>>>> defined?
> > > >>>>
> > > >>>>> That makes sense. I'm ok with FSYNC.
> > > >>>>>> Anton, I don't understand why we should rename LOG_ONLY to SYNC.
> > We
> > > >>>>>> started this discussion with bad naming of DEFAULT, but this has
> > > >>>>>>
> > > >>>>> nothing
> > > >>>>
> > > >>>>> to
> > > >>>>>
> > > >>>>>> do with LOG_ONLY (even though it may be scientific - but SYNC
> > sounds
> > > >>>>>> scientific as well).
> > > >>>>>>
> > > >>>>>> I agree with Ivan, we should not go wild with renaming.
> However, I
> > > >>>>>
> > > >>>> would
> > > >>>
> > > >>>> like to find out what is the meaning behind the LOG_ONLY name. Can
> > > >>>>>
> > > >>>> someone
> > > >>>>
> > > >>>>> explain?
> > > >>>>>
> > > >>>>> D.
> > > >>>>>
> > > >>>>>
> > > >>>>
> > > >>>> --
> > > >>>> Best regards,
> > > >>>> Ilya
> > > >>>>
> > > >>>>
> > > >
> > >
> >
>

[Dmitriy Pavlov]

Thank you. Data can't be corrupted in case crash because of WAL replay
(since completed checkpoint). Physical records are used to restore probably
corrupted pages in persistent store (we overwrite so called 'grey zone' -
pages we don't know for sure if they have been written).

Only one effect is unwritten one or several last transactions. It is not
the same with corrupted data.

пт, 16 февр. 2018 г. в 19:19, Vladimir Ozerov <[hidden email]>:

> Log only mode is not safe - data might be corrupted in case of system
> crash. Oracle - fsync, Postgres - fsync, SQL Server - fsync, Cassandra -
> similar to our “background”.
>
> пт, 16 февр. 2018 г. в 19:11, Dmitry Pavlov <[hidden email]>:
>
> > Hi Vladimir,
> >
> > What you saying is defenetely make sence.
> >
> > In the same time LOG_ONLY is also safe mode, user will be able to restore
> > system after crash. If it is not true, we should create critical ticket
> and
> > fix it.
> >
> > Do you know other databases defaults, such as Cassandra, Oracle, Postgre?
> >
> > Sincerely,
> > Dmitriy Pavlov
> >
> > пт, 16 февр. 2018 г. в 18:41, Vladimir Ozerov <[hidden email]>:
> >
> > > Igniters,
> > >
> > > Sorry for pouring oil on the flames, but from database perspective
> moving
> > > from FSYNC to non-FSYNC mode appears to be a mistake. When you work
> with
> > > database, your main expectation is that it will save your data. All
> > > production database vendor make sure that you are safe, not that you
> are
> > > fast. Moreover, some vendors even prevent you from being in unsafe mode
> > > (e.g. you cannot disable fsync in SQL Server at all).
> > >
> > > If we continue going in this direction, we will end up with a product,
> > > which is unsafe out of the box and require tons of documentation to
> > > understand how to make it safe. Definitely not the right message to the
> > > market. This is like a car without brakes - would you like to drive it?
> > If
> > > this is Need For Speed game and you have unlimited lives (in-memory
> cache
> > > with backing store), then yes. If this is a real life with
> (persistence)
> > -
> > > then no.
> > >
> > > On Fri, Feb 16, 2018 at 5:20 PM, Dmitriy Setrakyan <
> > [hidden email]>
> > > wrote:
> > >
> > > > Well, I cannot say that I like the name LOG_ONLY, but I would vote to
> > > keep
> > > > it for now, given that it is already documented in many places,
> blogs,
> > > and
> > > > examples.
> > > >
> > > > D.
> > > >
> > > > On Fri, Feb 16, 2018 at 8:13 AM, Ivan Rakov <[hidden email]>
> > > wrote:
> > > >
> > > > > Looks like it's an Ignite term - I've never heard of it outside
> > Ignite
> > > > > scope.
> > > > >
> > > > > Though, renaming existing enum value requires keeping old as
> > > deprecated.
> > > > > DEFAULT is confusing enough to pay this price.
> > > > > As for LOG_ONLY, I think we can keep it as long as it has good and
> > > > > definitive javadoc.
> > > > >
> > > > > Best Regards,
> > > > > Ivan Rakov
> > > > >
> > > > >
> > > > > On 16.02.2018 17:07, Dmitriy Setrakyan wrote:
> > > > >
> > > > >> Igniters, just to clarify, does the term LOG_ONLY mean anything in
> > the
> > > > >> industry or is this just an Ignite term?
> > > > >>
> > > > >> D.
> > > > >>
> > > > >> On Fri, Feb 16, 2018 at 8:03 AM, Anton Vinogradov <
> > > > >> [hidden email]>
> > > > >> wrote:
> > > > >>
> > > > >> Log only mode: flushes application buffers.
> > > > >>> So, in synced mode without fsync guarantee. That's why I propose
> to
> > > > >>> rename
> > > > >>> it as SYNC.
> > > > >>>
> > > > >>> On Fri, Feb 16, 2018 at 4:49 PM, Ilya Lantukh <
> > [hidden email]
> > > >
> > > > >>> wrote:
> > > > >>>
> > > > >>> I am OK with either FSYNC or STRICT variant.
> > > > >>>>
> > > > >>>> LOG_ONLY name means "log without fsync".
> > > > >>>>
> > > > >>>> On Fri, Feb 16, 2018 at 4:05 PM, Dmitriy Setrakyan <
> > > > >>>>
> > > > >>> [hidden email]>
> > > > >>>
> > > > >>>> wrote:
> > > > >>>>
> > > > >>>> On Fri, Feb 16, 2018 at 7:02 AM, Ivan Rakov <
> > [hidden email]>
> > > > >>>>>
> > > > >>>> wrote:
> > > > >>>>
> > > > >>>>> Why create a new term to define something that has already been
> > > > >>>>>>
> > > > >>>>> defined?
> > > > >>>>
> > > > >>>>> That makes sense. I'm ok with FSYNC.
> > > > >>>>>> Anton, I don't understand why we should rename LOG_ONLY to
> SYNC.
> > > We
> > > > >>>>>> started this discussion with bad naming of DEFAULT, but this
> has
> > > > >>>>>>
> > > > >>>>> nothing
> > > > >>>>
> > > > >>>>> to
> > > > >>>>>
> > > > >>>>>> do with LOG_ONLY (even though it may be scientific - but SYNC
> > > sounds
> > > > >>>>>> scientific as well).
> > > > >>>>>>
> > > > >>>>>> I agree with Ivan, we should not go wild with renaming.
> > However, I
> > > > >>>>>
> > > > >>>> would
> > > > >>>
> > > > >>>> like to find out what is the meaning behind the LOG_ONLY name.
> Can
> > > > >>>>>
> > > > >>>> someone
> > > > >>>>
> > > > >>>>> explain?
> > > > >>>>>
> > > > >>>>> D.
> > > > >>>>>
> > > > >>>>>
> > > > >>>>
> > > > >>>> --
> > > > >>>> Best regards,
> > > > >>>> Ilya
> > > > >>>>
> > > > >>>>
> > > > >
> > > >
> > >
> >
>

[Vladimir Ozerov]

What is the reason to have DEFAULT mode at all if you claim LOG_ONLY to be
completely safe? :)

And how it could be safe provided that without fsync we loose part of WAL
itself in case of crash?

пт, 16 февр. 2018 г. в 19:32, Dmitry Pavlov <[hidden email]>:

> Thank you. Data can't be corrupted in case crash because of WAL replay
> (since completed checkpoint). Physical records are used to restore probably
> corrupted pages in persistent store (we overwrite so called 'grey zone' -
> pages we don't know for sure if they have been written).
>
> Only one effect is unwritten one or several last transactions. It is not
> the same with corrupted data.
>
> пт, 16 февр. 2018 г. в 19:19, Vladimir Ozerov <[hidden email]>:
>
> > Log only mode is not safe - data might be corrupted in case of system
> > crash. Oracle - fsync, Postgres - fsync, SQL Server - fsync, Cassandra -
> > similar to our “background”.
> >
> > пт, 16 февр. 2018 г. в 19:11, Dmitry Pavlov <[hidden email]>:
> >
> > > Hi Vladimir,
> > >
> > > What you saying is defenetely make sence.
> > >
> > > In the same time LOG_ONLY is also safe mode, user will be able to
> restore
> > > system after crash. If it is not true, we should create critical ticket
> > and
> > > fix it.
> > >
> > > Do you know other databases defaults, such as Cassandra, Oracle,
> Postgre?
> > >
> > > Sincerely,
> > > Dmitriy Pavlov
> > >
> > > пт, 16 февр. 2018 г. в 18:41, Vladimir Ozerov <[hidden email]>:
> > >
> > > > Igniters,
> > > >
> > > > Sorry for pouring oil on the flames, but from database perspective
> > moving
> > > > from FSYNC to non-FSYNC mode appears to be a mistake. When you work
> > with
> > > > database, your main expectation is that it will save your data. All
> > > > production database vendor make sure that you are safe, not that you
> > are
> > > > fast. Moreover, some vendors even prevent you from being in unsafe
> mode
> > > > (e.g. you cannot disable fsync in SQL Server at all).
> > > >
> > > > If we continue going in this direction, we will end up with a
> product,
> > > > which is unsafe out of the box and require tons of documentation to
> > > > understand how to make it safe. Definitely not the right message to
> the
> > > > market. This is like a car without brakes - would you like to drive
> it?
> > > If
> > > > this is Need For Speed game and you have unlimited lives (in-memory
> > cache
> > > > with backing store), then yes. If this is a real life with
> > (persistence)
> > > -
> > > > then no.
> > > >
> > > > On Fri, Feb 16, 2018 at 5:20 PM, Dmitriy Setrakyan <
> > > [hidden email]>
> > > > wrote:
> > > >
> > > > > Well, I cannot say that I like the name LOG_ONLY, but I would vote
> to
> > > > keep
> > > > > it for now, given that it is already documented in many places,
> > blogs,
> > > > and
> > > > > examples.
> > > > >
> > > > > D.
> > > > >
> > > > > On Fri, Feb 16, 2018 at 8:13 AM, Ivan Rakov <[hidden email]
> >
> > > > wrote:
> > > > >
> > > > > > Looks like it's an Ignite term - I've never heard of it outside
> > > Ignite
> > > > > > scope.
> > > > > >
> > > > > > Though, renaming existing enum value requires keeping old as
> > > > deprecated.
> > > > > > DEFAULT is confusing enough to pay this price.
> > > > > > As for LOG_ONLY, I think we can keep it as long as it has good
> and
> > > > > > definitive javadoc.
> > > > > >
> > > > > > Best Regards,
> > > > > > Ivan Rakov
> > > > > >
> > > > > >
> > > > > > On 16.02.2018 17:07, Dmitriy Setrakyan wrote:
> > > > > >
> > > > > >> Igniters, just to clarify, does the term LOG_ONLY mean anything
> in
> > > the
> > > > > >> industry or is this just an Ignite term?
> > > > > >>
> > > > > >> D.
> > > > > >>
> > > > > >> On Fri, Feb 16, 2018 at 8:03 AM, Anton Vinogradov <
> > > > > >> [hidden email]>
> > > > > >> wrote:
> > > > > >>
> > > > > >> Log only mode: flushes application buffers.
> > > > > >>> So, in synced mode without fsync guarantee. That's why I
> propose
> > to
> > > > > >>> rename
> > > > > >>> it as SYNC.
> > > > > >>>
> > > > > >>> On Fri, Feb 16, 2018 at 4:49 PM, Ilya Lantukh <
> > > [hidden email]
> > > > >
> > > > > >>> wrote:
> > > > > >>>
> > > > > >>> I am OK with either FSYNC or STRICT variant.
> > > > > >>>>
> > > > > >>>> LOG_ONLY name means "log without fsync".
> > > > > >>>>
> > > > > >>>> On Fri, Feb 16, 2018 at 4:05 PM, Dmitriy Setrakyan <
> > > > > >>>>
> > > > > >>> [hidden email]>
> > > > > >>>
> > > > > >>>> wrote:
> > > > > >>>>
> > > > > >>>> On Fri, Feb 16, 2018 at 7:02 AM, Ivan Rakov <
> > > [hidden email]>
> > > > > >>>>>
> > > > > >>>> wrote:
> > > > > >>>>
> > > > > >>>>> Why create a new term to define something that has already
> been
> > > > > >>>>>>
> > > > > >>>>> defined?
> > > > > >>>>
> > > > > >>>>> That makes sense. I'm ok with FSYNC.
> > > > > >>>>>> Anton, I don't understand why we should rename LOG_ONLY to
> > SYNC.
> > > > We
> > > > > >>>>>> started this discussion with bad naming of DEFAULT, but this
> > has
> > > > > >>>>>>
> > > > > >>>>> nothing
> > > > > >>>>
> > > > > >>>>> to
> > > > > >>>>>
> > > > > >>>>>> do with LOG_ONLY (even though it may be scientific - but
> SYNC
> > > > sounds
> > > > > >>>>>> scientific as well).
> > > > > >>>>>>
> > > > > >>>>>> I agree with Ivan, we should not go wild with renaming.
> > > However, I
> > > > > >>>>>
> > > > > >>>> would
> > > > > >>>
> > > > > >>>> like to find out what is the meaning behind the LOG_ONLY name.
> > Can
> > > > > >>>>>
> > > > > >>>> someone
> > > > > >>>>
> > > > > >>>>> explain?
> > > > > >>>>>
> > > > > >>>>> D.
> > > > > >>>>>
> > > > > >>>>>
> > > > > >>>>
> > > > > >>>> --
> > > > > >>>> Best regards,
> > > > > >>>> Ilya
> > > > > >>>>
> > > > > >>>>
> > > > > >
> > > > >
> > > >
> > >
> >
>

[Valentin Kulichenko]

Guys,

While we're on this topic, what is the difference between BACKGROUND and
NONE in terms of semantics and provided guarantees? To me it looks like
both guarantee to recover the state since last checkpoint and anything else
can potentially be lost, so from user perspective they are the same. Am I
missing something here?

Also there is the following in Javadoc for NONE: "If an Ignite node is
terminated in NONE mode abruptly, it is likely that the data stored on disk
is corrupted and work directory will need to be cleared for a node
restart.". If this is really the case, I'm not sure NONE makes sense at
all. Why would I enable persistence if I'm likely to clear the storage on
restart?

-Val

On Fri, Feb 16, 2018 at 8:39 AM, Vladimir Ozerov <[hidden email]>
wrote:

> What is the reason to have DEFAULT mode at all if you claim LOG_ONLY to be
> completely safe? :)
>
> And how it could be safe provided that without fsync we loose part of WAL
> itself in case of crash?
>
> пт, 16 февр. 2018 г. в 19:32, Dmitry Pavlov <[hidden email]>:
>
> > Thank you. Data can't be corrupted in case crash because of WAL replay
> > (since completed checkpoint). Physical records are used to restore
> probably
> > corrupted pages in persistent store (we overwrite so called 'grey zone' -
> > pages we don't know for sure if they have been written).
> >
> > Only one effect is unwritten one or several last transactions. It is not
> > the same with corrupted data.
> >
> > пт, 16 февр. 2018 г. в 19:19, Vladimir Ozerov <[hidden email]>:
> >
> > > Log only mode is not safe - data might be corrupted in case of system
> > > crash. Oracle - fsync, Postgres - fsync, SQL Server - fsync, Cassandra
> -
> > > similar to our “background”.
> > >
> > > пт, 16 февр. 2018 г. в 19:11, Dmitry Pavlov <[hidden email]>:
> > >
> > > > Hi Vladimir,
> > > >
> > > > What you saying is defenetely make sence.
> > > >
> > > > In the same time LOG_ONLY is also safe mode, user will be able to
> > restore
> > > > system after crash. If it is not true, we should create critical
> ticket
> > > and
> > > > fix it.
> > > >
> > > > Do you know other databases defaults, such as Cassandra, Oracle,
> > Postgre?
> > > >
> > > > Sincerely,
> > > > Dmitriy Pavlov
> > > >
> > > > пт, 16 февр. 2018 г. в 18:41, Vladimir Ozerov <[hidden email]
> >:
> > > >
> > > > > Igniters,
> > > > >
> > > > > Sorry for pouring oil on the flames, but from database perspective
> > > moving
> > > > > from FSYNC to non-FSYNC mode appears to be a mistake. When you work
> > > with
> > > > > database, your main expectation is that it will save your data. All
> > > > > production database vendor make sure that you are safe, not that
> you
> > > are
> > > > > fast. Moreover, some vendors even prevent you from being in unsafe
> > mode
> > > > > (e.g. you cannot disable fsync in SQL Server at all).
> > > > >
> > > > > If we continue going in this direction, we will end up with a
> > product,
> > > > > which is unsafe out of the box and require tons of documentation to
> > > > > understand how to make it safe. Definitely not the right message to
> > the
> > > > > market. This is like a car without brakes - would you like to drive
> > it?
> > > > If
> > > > > this is Need For Speed game and you have unlimited lives (in-memory
> > > cache
> > > > > with backing store), then yes. If this is a real life with
> > > (persistence)
> > > > -
> > > > > then no.
> > > > >
> > > > > On Fri, Feb 16, 2018 at 5:20 PM, Dmitriy Setrakyan <
> > > > [hidden email]>
> > > > > wrote:
> > > > >
> > > > > > Well, I cannot say that I like the name LOG_ONLY, but I would
> vote
> > to
> > > > > keep
> > > > > > it for now, given that it is already documented in many places,
> > > blogs,
> > > > > and
> > > > > > examples.
> > > > > >
> > > > > > D.
> > > > > >
> > > > > > On Fri, Feb 16, 2018 at 8:13 AM, Ivan Rakov <
> [hidden email]
> > >
> > > > > wrote:
> > > > > >
> > > > > > > Looks like it's an Ignite term - I've never heard of it outside
> > > > Ignite
> > > > > > > scope.
> > > > > > >
> > > > > > > Though, renaming existing enum value requires keeping old as
> > > > > deprecated.
> > > > > > > DEFAULT is confusing enough to pay this price.
> > > > > > > As for LOG_ONLY, I think we can keep it as long as it has good
> > and
> > > > > > > definitive javadoc.
> > > > > > >
> > > > > > > Best Regards,
> > > > > > > Ivan Rakov
> > > > > > >
> > > > > > >
> > > > > > > On 16.02.2018 17:07, Dmitriy Setrakyan wrote:
> > > > > > >
> > > > > > >> Igniters, just to clarify, does the term LOG_ONLY mean
> anything
> > in
> > > > the
> > > > > > >> industry or is this just an Ignite term?
> > > > > > >>
> > > > > > >> D.
> > > > > > >>
> > > > > > >> On Fri, Feb 16, 2018 at 8:03 AM, Anton Vinogradov <
> > > > > > >> [hidden email]>
> > > > > > >> wrote:
> > > > > > >>
> > > > > > >> Log only mode: flushes application buffers.
> > > > > > >>> So, in synced mode without fsync guarantee. That's why I
> > propose
> > > to
> > > > > > >>> rename
> > > > > > >>> it as SYNC.
> > > > > > >>>
> > > > > > >>> On Fri, Feb 16, 2018 at 4:49 PM, Ilya Lantukh <
> > > > [hidden email]
> > > > > >
> > > > > > >>> wrote:
> > > > > > >>>
> > > > > > >>> I am OK with either FSYNC or STRICT variant.
> > > > > > >>>>
> > > > > > >>>> LOG_ONLY name means "log without fsync".
> > > > > > >>>>
> > > > > > >>>> On Fri, Feb 16, 2018 at 4:05 PM, Dmitriy Setrakyan <
> > > > > > >>>>
> > > > > > >>> [hidden email]>
> > > > > > >>>
> > > > > > >>>> wrote:
> > > > > > >>>>
> > > > > > >>>> On Fri, Feb 16, 2018 at 7:02 AM, Ivan Rakov <
> > > > [hidden email]>
> > > > > > >>>>>
> > > > > > >>>> wrote:
> > > > > > >>>>
> > > > > > >>>>> Why create a new term to define something that has already
> > been
> > > > > > >>>>>>
> > > > > > >>>>> defined?
> > > > > > >>>>
> > > > > > >>>>> That makes sense. I'm ok with FSYNC.
> > > > > > >>>>>> Anton, I don't understand why we should rename LOG_ONLY to
> > > SYNC.
> > > > > We
> > > > > > >>>>>> started this discussion with bad naming of DEFAULT, but
> this
> > > has
> > > > > > >>>>>>
> > > > > > >>>>> nothing
> > > > > > >>>>
> > > > > > >>>>> to
> > > > > > >>>>>
> > > > > > >>>>>> do with LOG_ONLY (even though it may be scientific - but
> > SYNC
> > > > > sounds
> > > > > > >>>>>> scientific as well).
> > > > > > >>>>>>
> > > > > > >>>>>> I agree with Ivan, we should not go wild with renaming.
> > > > However, I
> > > > > > >>>>>
> > > > > > >>>> would
> > > > > > >>>
> > > > > > >>>> like to find out what is the meaning behind the LOG_ONLY
> name.
> > > Can
> > > > > > >>>>>
> > > > > > >>>> someone
> > > > > > >>>>
> > > > > > >>>>> explain?
> > > > > > >>>>>
> > > > > > >>>>> D.
> > > > > > >>>>>
> > > > > > >>>>>
> > > > > > >>>>
> > > > > > >>>> --
> > > > > > >>>> Best regards,
> > > > > > >>>> Ilya
> > > > > > >>>>
> > > > > > >>>>
> > > > > > >
> > > > > >
> > > > >
> > > >
> > >
> >
>

[Dmitriy Pavlov]

Hi, all WAL modes except NONE protects from data consistency problem
(B+Tree, pages, etc), which is why I suggest to avoid saying 'corrupted'
about 'unapplied updates'.

Log Only and Background may cause unapplied updates in case of OS/process
failures.

None mode IMO is not an option in case data consistency is needed.

пт, 16 февр. 2018 г. в 20:49, Valentin Kulichenko <
[hidden email]>:

> Guys,
>
> While we're on this topic, what is the difference between BACKGROUND and
> NONE in terms of semantics and provided guarantees? To me it looks like
> both guarantee to recover the state since last checkpoint and anything else
> can potentially be lost, so from user perspective they are the same. Am I
> missing something here?
>
> Also there is the following in Javadoc for NONE: "If an Ignite node is
> terminated in NONE mode abruptly, it is likely that the data stored on disk
> is corrupted and work directory will need to be cleared for a node
> restart.". If this is really the case, I'm not sure NONE makes sense at
> all. Why would I enable persistence if I'm likely to clear the storage on
> restart?
>
> -Val
>
> On Fri, Feb 16, 2018 at 8:39 AM, Vladimir Ozerov <[hidden email]>
> wrote:
>
> > What is the reason to have DEFAULT mode at all if you claim LOG_ONLY to
> be
> > completely safe? :)
> >
> > And how it could be safe provided that without fsync we loose part of WAL
> > itself in case of crash?
> >
> > пт, 16 февр. 2018 г. в 19:32, Dmitry Pavlov <[hidden email]>:
> >
> > > Thank you. Data can't be corrupted in case crash because of WAL replay
> > > (since completed checkpoint). Physical records are used to restore
> > probably
> > > corrupted pages in persistent store (we overwrite so called 'grey
> zone' -
> > > pages we don't know for sure if they have been written).
> > >
> > > Only one effect is unwritten one or several last transactions. It is
> not
> > > the same with corrupted data.
> > >
> > > пт, 16 февр. 2018 г. в 19:19, Vladimir Ozerov <[hidden email]>:
> > >
> > > > Log only mode is not safe - data might be corrupted in case of system
> > > > crash. Oracle - fsync, Postgres - fsync, SQL Server - fsync,
> Cassandra
> > -
> > > > similar to our “background”.
> > > >
> > > > пт, 16 февр. 2018 г. в 19:11, Dmitry Pavlov <[hidden email]>:
> > > >
> > > > > Hi Vladimir,
> > > > >
> > > > > What you saying is defenetely make sence.
> > > > >
> > > > > In the same time LOG_ONLY is also safe mode, user will be able to
> > > restore
> > > > > system after crash. If it is not true, we should create critical
> > ticket
> > > > and
> > > > > fix it.
> > > > >
> > > > > Do you know other databases defaults, such as Cassandra, Oracle,
> > > Postgre?
> > > > >
> > > > > Sincerely,
> > > > > Dmitriy Pavlov
> > > > >
> > > > > пт, 16 февр. 2018 г. в 18:41, Vladimir Ozerov <
> [hidden email]
> > >:
> > > > >
> > > > > > Igniters,
> > > > > >
> > > > > > Sorry for pouring oil on the flames, but from database
> perspective
> > > > moving
> > > > > > from FSYNC to non-FSYNC mode appears to be a mistake. When you
> work
> > > > with
> > > > > > database, your main expectation is that it will save your data.
> All
> > > > > > production database vendor make sure that you are safe, not that
> > you
> > > > are
> > > > > > fast. Moreover, some vendors even prevent you from being in
> unsafe
> > > mode
> > > > > > (e.g. you cannot disable fsync in SQL Server at all).
> > > > > >
> > > > > > If we continue going in this direction, we will end up with a
> > > product,
> > > > > > which is unsafe out of the box and require tons of documentation
> to
> > > > > > understand how to make it safe. Definitely not the right message
> to
> > > the
> > > > > > market. This is like a car without brakes - would you like to
> drive
> > > it?
> > > > > If
> > > > > > this is Need For Speed game and you have unlimited lives
> (in-memory
> > > > cache
> > > > > > with backing store), then yes. If this is a real life with
> > > > (persistence)
> > > > > -
> > > > > > then no.
> > > > > >
> > > > > > On Fri, Feb 16, 2018 at 5:20 PM, Dmitriy Setrakyan <
> > > > > [hidden email]>
> > > > > > wrote:
> > > > > >
> > > > > > > Well, I cannot say that I like the name LOG_ONLY, but I would
> > vote
> > > to
> > > > > > keep
> > > > > > > it for now, given that it is already documented in many places,
> > > > blogs,
> > > > > > and
> > > > > > > examples.
> > > > > > >
> > > > > > > D.
> > > > > > >
> > > > > > > On Fri, Feb 16, 2018 at 8:13 AM, Ivan Rakov <
> > [hidden email]
> > > >
> > > > > > wrote:
> > > > > > >
> > > > > > > > Looks like it's an Ignite term - I've never heard of it
> outside
> > > > > Ignite
> > > > > > > > scope.
> > > > > > > >
> > > > > > > > Though, renaming existing enum value requires keeping old as
> > > > > > deprecated.
> > > > > > > > DEFAULT is confusing enough to pay this price.
> > > > > > > > As for LOG_ONLY, I think we can keep it as long as it has
> good
> > > and
> > > > > > > > definitive javadoc.
> > > > > > > >
> > > > > > > > Best Regards,
> > > > > > > > Ivan Rakov
> > > > > > > >
> > > > > > > >
> > > > > > > > On 16.02.2018 17:07, Dmitriy Setrakyan wrote:
> > > > > > > >
> > > > > > > >> Igniters, just to clarify, does the term LOG_ONLY mean
> > anything
> > > in
> > > > > the
> > > > > > > >> industry or is this just an Ignite term?
> > > > > > > >>
> > > > > > > >> D.
> > > > > > > >>
> > > > > > > >> On Fri, Feb 16, 2018 at 8:03 AM, Anton Vinogradov <
> > > > > > > >> [hidden email]>
> > > > > > > >> wrote:
> > > > > > > >>
> > > > > > > >> Log only mode: flushes application buffers.
> > > > > > > >>> So, in synced mode without fsync guarantee. That's why I
> > > propose
> > > > to
> > > > > > > >>> rename
> > > > > > > >>> it as SYNC.
> > > > > > > >>>
> > > > > > > >>> On Fri, Feb 16, 2018 at 4:49 PM, Ilya Lantukh <
> > > > > [hidden email]
> > > > > > >
> > > > > > > >>> wrote:
> > > > > > > >>>
> > > > > > > >>> I am OK with either FSYNC or STRICT variant.
> > > > > > > >>>>
> > > > > > > >>>> LOG_ONLY name means "log without fsync".
> > > > > > > >>>>
> > > > > > > >>>> On Fri, Feb 16, 2018 at 4:05 PM, Dmitriy Setrakyan <
> > > > > > > >>>>
> > > > > > > >>> [hidden email]>
> > > > > > > >>>
> > > > > > > >>>> wrote:
> > > > > > > >>>>
> > > > > > > >>>> On Fri, Feb 16, 2018 at 7:02 AM, Ivan Rakov <
> > > > > [hidden email]>
> > > > > > > >>>>>
> > > > > > > >>>> wrote:
> > > > > > > >>>>
> > > > > > > >>>>> Why create a new term to define something that has
> already
> > > been
> > > > > > > >>>>>>
> > > > > > > >>>>> defined?
> > > > > > > >>>>
> > > > > > > >>>>> That makes sense. I'm ok with FSYNC.
> > > > > > > >>>>>> Anton, I don't understand why we should rename LOG_ONLY
> to
> > > > SYNC.
> > > > > > We
> > > > > > > >>>>>> started this discussion with bad naming of DEFAULT, but
> > this
> > > > has
> > > > > > > >>>>>>
> > > > > > > >>>>> nothing
> > > > > > > >>>>
> > > > > > > >>>>> to
> > > > > > > >>>>>
> > > > > > > >>>>>> do with LOG_ONLY (even though it may be scientific - but
> > > SYNC
> > > > > > sounds
> > > > > > > >>>>>> scientific as well).
> > > > > > > >>>>>>
> > > > > > > >>>>>> I agree with Ivan, we should not go wild with renaming.
> > > > > However, I
> > > > > > > >>>>>
> > > > > > > >>>> would
> > > > > > > >>>
> > > > > > > >>>> like to find out what is the meaning behind the LOG_ONLY
> > name.
> > > > Can
> > > > > > > >>>>>
> > > > > > > >>>> someone
> > > > > > > >>>>
> > > > > > > >>>>> explain?
> > > > > > > >>>>>
> > > > > > > >>>>> D.
> > > > > > > >>>>>
> > > > > > > >>>>>
> > > > > > > >>>>
> > > > > > > >>>> --
> > > > > > > >>>> Best regards,
> > > > > > > >>>> Ilya
> > > > > > > >>>>
> > > > > > > >>>>
> > > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > >
> > >
> >
>

[Sergey Kozlov]

I suppose some approaches used by classic databases makes no sense for
Ignite. FSYNC requirement for databases has the nature of single host
solution. If you have corrupted db files you have corrupted (lost) data.

For Ignite the enough number of backups and the failure detecting logic can
provide the data consistency in term "cluster data consistency".



On Fri, Feb 16, 2018 at 8:57 PM, Dmitry Pavlov <[hidden email]>
wrote:

> Hi, all WAL modes except NONE protects from data consistency problem
> (B+Tree, pages, etc), which is why I suggest to avoid saying 'corrupted'
> about 'unapplied updates'.
>
> Log Only and Background may cause unapplied updates in case of OS/process
> failures.
>
> None mode IMO is not an option in case data consistency is needed.
>
> пт, 16 февр. 2018 г. в 20:49, Valentin Kulichenko <
> [hidden email]>:
>
> > Guys,
> >
> > While we're on this topic, what is the difference between BACKGROUND and
> > NONE in terms of semantics and provided guarantees? To me it looks like
> > both guarantee to recover the state since last checkpoint and anything
> else
> > can potentially be lost, so from user perspective they are the same. Am I
> > missing something here?
> >
> > Also there is the following in Javadoc for NONE: "If an Ignite node is
> > terminated in NONE mode abruptly, it is likely that the data stored on
> disk
> > is corrupted and work directory will need to be cleared for a node
> > restart.". If this is really the case, I'm not sure NONE makes sense at
> > all. Why would I enable persistence if I'm likely to clear the storage on
> > restart?
> >
> > -Val
> >
> > On Fri, Feb 16, 2018 at 8:39 AM, Vladimir Ozerov <[hidden email]>
> > wrote:
> >
> > > What is the reason to have DEFAULT mode at all if you claim LOG_ONLY to
> > be
> > > completely safe? :)
> > >
> > > And how it could be safe provided that without fsync we loose part of
> WAL
> > > itself in case of crash?
> > >
> > > пт, 16 февр. 2018 г. в 19:32, Dmitry Pavlov <[hidden email]>:
> > >
> > > > Thank you. Data can't be corrupted in case crash because of WAL
> replay
> > > > (since completed checkpoint). Physical records are used to restore
> > > probably
> > > > corrupted pages in persistent store (we overwrite so called 'grey
> > zone' -
> > > > pages we don't know for sure if they have been written).
> > > >
> > > > Only one effect is unwritten one or several last transactions. It is
> > not
> > > > the same with corrupted data.
> > > >
> > > > пт, 16 февр. 2018 г. в 19:19, Vladimir Ozerov <[hidden email]
> >:
> > > >
> > > > > Log only mode is not safe - data might be corrupted in case of
> system
> > > > > crash. Oracle - fsync, Postgres - fsync, SQL Server - fsync,
> > Cassandra
> > > -
> > > > > similar to our “background”.
> > > > >
> > > > > пт, 16 февр. 2018 г. в 19:11, Dmitry Pavlov <[hidden email]
> >:
> > > > >
> > > > > > Hi Vladimir,
> > > > > >
> > > > > > What you saying is defenetely make sence.
> > > > > >
> > > > > > In the same time LOG_ONLY is also safe mode, user will be able to
> > > > restore
> > > > > > system after crash. If it is not true, we should create critical
> > > ticket
> > > > > and
> > > > > > fix it.
> > > > > >
> > > > > > Do you know other databases defaults, such as Cassandra, Oracle,
> > > > Postgre?
> > > > > >
> > > > > > Sincerely,
> > > > > > Dmitriy Pavlov
> > > > > >
> > > > > > пт, 16 февр. 2018 г. в 18:41, Vladimir Ozerov <
> > [hidden email]
> > > >:
> > > > > >
> > > > > > > Igniters,
> > > > > > >
> > > > > > > Sorry for pouring oil on the flames, but from database
> > perspective
> > > > > moving
> > > > > > > from FSYNC to non-FSYNC mode appears to be a mistake. When you
> > work
> > > > > with
> > > > > > > database, your main expectation is that it will save your data.
> > All
> > > > > > > production database vendor make sure that you are safe, not
> that
> > > you
> > > > > are
> > > > > > > fast. Moreover, some vendors even prevent you from being in
> > unsafe
> > > > mode
> > > > > > > (e.g. you cannot disable fsync in SQL Server at all).
> > > > > > >
> > > > > > > If we continue going in this direction, we will end up with a
> > > > product,
> > > > > > > which is unsafe out of the box and require tons of
> documentation
> > to
> > > > > > > understand how to make it safe. Definitely not the right
> message
> > to
> > > > the
> > > > > > > market. This is like a car without brakes - would you like to
> > drive
> > > > it?
> > > > > > If
> > > > > > > this is Need For Speed game and you have unlimited lives
> > (in-memory
> > > > > cache
> > > > > > > with backing store), then yes. If this is a real life with
> > > > > (persistence)
> > > > > > -
> > > > > > > then no.
> > > > > > >
> > > > > > > On Fri, Feb 16, 2018 at 5:20 PM, Dmitriy Setrakyan <
> > > > > > [hidden email]>
> > > > > > > wrote:
> > > > > > >
> > > > > > > > Well, I cannot say that I like the name LOG_ONLY, but I would
> > > vote
> > > > to
> > > > > > > keep
> > > > > > > > it for now, given that it is already documented in many
> places,
> > > > > blogs,
> > > > > > > and
> > > > > > > > examples.
> > > > > > > >
> > > > > > > > D.
> > > > > > > >
> > > > > > > > On Fri, Feb 16, 2018 at 8:13 AM, Ivan Rakov <
> > > [hidden email]
> > > > >
> > > > > > > wrote:
> > > > > > > >
> > > > > > > > > Looks like it's an Ignite term - I've never heard of it
> > outside
> > > > > > Ignite
> > > > > > > > > scope.
> > > > > > > > >
> > > > > > > > > Though, renaming existing enum value requires keeping old
> as
> > > > > > > deprecated.
> > > > > > > > > DEFAULT is confusing enough to pay this price.
> > > > > > > > > As for LOG_ONLY, I think we can keep it as long as it has
> > good
> > > > and
> > > > > > > > > definitive javadoc.
> > > > > > > > >
> > > > > > > > > Best Regards,
> > > > > > > > > Ivan Rakov
> > > > > > > > >
> > > > > > > > >
> > > > > > > > > On 16.02.2018 17:07, Dmitriy Setrakyan wrote:
> > > > > > > > >
> > > > > > > > >> Igniters, just to clarify, does the term LOG_ONLY mean
> > > anything
> > > > in
> > > > > > the
> > > > > > > > >> industry or is this just an Ignite term?
> > > > > > > > >>
> > > > > > > > >> D.
> > > > > > > > >>
> > > > > > > > >> On Fri, Feb 16, 2018 at 8:03 AM, Anton Vinogradov <
> > > > > > > > >> [hidden email]>
> > > > > > > > >> wrote:
> > > > > > > > >>
> > > > > > > > >> Log only mode: flushes application buffers.
> > > > > > > > >>> So, in synced mode without fsync guarantee. That's why I
> > > > propose
> > > > > to
> > > > > > > > >>> rename
> > > > > > > > >>> it as SYNC.
> > > > > > > > >>>
> > > > > > > > >>> On Fri, Feb 16, 2018 at 4:49 PM, Ilya Lantukh <
> > > > > > [hidden email]
> > > > > > > >
> > > > > > > > >>> wrote:
> > > > > > > > >>>
> > > > > > > > >>> I am OK with either FSYNC or STRICT variant.
> > > > > > > > >>>>
> > > > > > > > >>>> LOG_ONLY name means "log without fsync".
> > > > > > > > >>>>
> > > > > > > > >>>> On Fri, Feb 16, 2018 at 4:05 PM, Dmitriy Setrakyan <
> > > > > > > > >>>>
> > > > > > > > >>> [hidden email]>
> > > > > > > > >>>
> > > > > > > > >>>> wrote:
> > > > > > > > >>>>
> > > > > > > > >>>> On Fri, Feb 16, 2018 at 7:02 AM, Ivan Rakov <
> > > > > > [hidden email]>
> > > > > > > > >>>>>
> > > > > > > > >>>> wrote:
> > > > > > > > >>>>
> > > > > > > > >>>>> Why create a new term to define something that has
> > already
> > > > been
> > > > > > > > >>>>>>
> > > > > > > > >>>>> defined?
> > > > > > > > >>>>
> > > > > > > > >>>>> That makes sense. I'm ok with FSYNC.
> > > > > > > > >>>>>> Anton, I don't understand why we should rename
> LOG_ONLY
> > to
> > > > > SYNC.
> > > > > > > We
> > > > > > > > >>>>>> started this discussion with bad naming of DEFAULT,
> but
> > > this
> > > > > has
> > > > > > > > >>>>>>
> > > > > > > > >>>>> nothing
> > > > > > > > >>>>
> > > > > > > > >>>>> to
> > > > > > > > >>>>>
> > > > > > > > >>>>>> do with LOG_ONLY (even though it may be scientific -
> but
> > > > SYNC
> > > > > > > sounds
> > > > > > > > >>>>>> scientific as well).
> > > > > > > > >>>>>>
> > > > > > > > >>>>>> I agree with Ivan, we should not go wild with
> renaming.
> > > > > > However, I
> > > > > > > > >>>>>
> > > > > > > > >>>> would
> > > > > > > > >>>
> > > > > > > > >>>> like to find out what is the meaning behind the LOG_ONLY
> > > name.
> > > > > Can
> > > > > > > > >>>>>
> > > > > > > > >>>> someone
> > > > > > > > >>>>
> > > > > > > > >>>>> explain?
> > > > > > > > >>>>>
> > > > > > > > >>>>> D.
> > > > > > > > >>>>>
> > > > > > > > >>>>>
> > > > > > > > >>>>
> > > > > > > > >>>> --
> > > > > > > > >>>> Best regards,
> > > > > > > > >>>> Ilya
> > > > > > > > >>>>
> > > > > > > > >>>>
> > > > > > > > >
> > > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > >
> > >
> >
>

--
Sergey Kozlov
GridGain Systems
www.gridgain.com

[Vladimir Ozerov]

Sergey,

We do not have backups by default either, so essentially we are loosing
data by default. Moreover, backups are less reliable option than fsync
because a lot of users cannot afford putting servers into separate power
circuits, so a single power failure may easily lead to poweroff of the
whole cluster at once, so data is lost still. This is normal practice even
for enterprise deployments (e.g. asynchronous replication).

To make things even worse, we employ PRIMARY_SYNC mode by default! So even
if you configured backups, you still may loose data due to a single node
failure - just shutdown the PRIMARY after commit is confirmed to the client
and your recent update will disappers.

So this is what user should do to make himself safe:
1) Learn about WAL modes
2) Learn about backups
3) Learn about synchronization modes
4) Cross his fingers that he understood everything correctly and that there
are no other hidden surprises in Ignite which could lead to data loss.

Way to much for a product, claiming to be A*C*ID and persistent, don't you
think so?

Leaving deafult WAL mode with fsync resolves all these issues.

Vladimir.


On Fri, Feb 16, 2018 at 11:43 PM, Sergey Kozlov <[hidden email]>
wrote:

> I suppose some approaches used by classic databases makes no sense for
> Ignite. FSYNC requirement for databases has the nature of single host
> solution. If you have corrupted db files you have corrupted (lost) data.
>
> For Ignite the enough number of backups and the failure detecting logic can
> provide the data consistency in term "cluster data consistency".
>
>
>
> On Fri, Feb 16, 2018 at 8:57 PM, Dmitry Pavlov <[hidden email]>
> wrote:
>
> > Hi, all WAL modes except NONE protects from data consistency problem
> > (B+Tree, pages, etc), which is why I suggest to avoid saying 'corrupted'
> > about 'unapplied updates'.
> >
> > Log Only and Background may cause unapplied updates in case of OS/process
> > failures.
> >
> > None mode IMO is not an option in case data consistency is needed.
> >
> > пт, 16 февр. 2018 г. в 20:49, Valentin Kulichenko <
> > [hidden email]>:
> >
> > > Guys,
> > >
> > > While we're on this topic, what is the difference between BACKGROUND
> and
> > > NONE in terms of semantics and provided guarantees? To me it looks like
> > > both guarantee to recover the state since last checkpoint and anything
> > else
> > > can potentially be lost, so from user perspective they are the same.
> Am I
> > > missing something here?
> > >
> > > Also there is the following in Javadoc for NONE: "If an Ignite node is
> > > terminated in NONE mode abruptly, it is likely that the data stored on
> > disk
> > > is corrupted and work directory will need to be cleared for a node
> > > restart.". If this is really the case, I'm not sure NONE makes sense at
> > > all. Why would I enable persistence if I'm likely to clear the storage
> on
> > > restart?
> > >
> > > -Val
> > >
> > > On Fri, Feb 16, 2018 at 8:39 AM, Vladimir Ozerov <[hidden email]
> >
> > > wrote:
> > >
> > > > What is the reason to have DEFAULT mode at all if you claim LOG_ONLY
> to
> > > be
> > > > completely safe? :)
> > > >
> > > > And how it could be safe provided that without fsync we loose part of
> > WAL
> > > > itself in case of crash?
> > > >
> > > > пт, 16 февр. 2018 г. в 19:32, Dmitry Pavlov <[hidden email]>:
> > > >
> > > > > Thank you. Data can't be corrupted in case crash because of WAL
> > replay
> > > > > (since completed checkpoint). Physical records are used to restore
> > > > probably
> > > > > corrupted pages in persistent store (we overwrite so called 'grey
> > > zone' -
> > > > > pages we don't know for sure if they have been written).
> > > > >
> > > > > Only one effect is unwritten one or several last transactions. It
> is
> > > not
> > > > > the same with corrupted data.
> > > > >
> > > > > пт, 16 февр. 2018 г. в 19:19, Vladimir Ozerov <
> [hidden email]
> > >:
> > > > >
> > > > > > Log only mode is not safe - data might be corrupted in case of
> > system
> > > > > > crash. Oracle - fsync, Postgres - fsync, SQL Server - fsync,
> > > Cassandra
> > > > -
> > > > > > similar to our “background”.
> > > > > >
> > > > > > пт, 16 февр. 2018 г. в 19:11, Dmitry Pavlov <
> [hidden email]
> > >:
> > > > > >
> > > > > > > Hi Vladimir,
> > > > > > >
> > > > > > > What you saying is defenetely make sence.
> > > > > > >
> > > > > > > In the same time LOG_ONLY is also safe mode, user will be able
> to
> > > > > restore
> > > > > > > system after crash. If it is not true, we should create
> critical
> > > > ticket
> > > > > > and
> > > > > > > fix it.
> > > > > > >
> > > > > > > Do you know other databases defaults, such as Cassandra,
> Oracle,
> > > > > Postgre?
> > > > > > >
> > > > > > > Sincerely,
> > > > > > > Dmitriy Pavlov
> > > > > > >
> > > > > > > пт, 16 февр. 2018 г. в 18:41, Vladimir Ozerov <
> > > [hidden email]
> > > > >:
> > > > > > >
> > > > > > > > Igniters,
> > > > > > > >
> > > > > > > > Sorry for pouring oil on the flames, but from database
> > > perspective
> > > > > > moving
> > > > > > > > from FSYNC to non-FSYNC mode appears to be a mistake. When
> you
> > > work
> > > > > > with
> > > > > > > > database, your main expectation is that it will save your
> data.
> > > All
> > > > > > > > production database vendor make sure that you are safe, not
> > that
> > > > you
> > > > > > are
> > > > > > > > fast. Moreover, some vendors even prevent you from being in
> > > unsafe
> > > > > mode
> > > > > > > > (e.g. you cannot disable fsync in SQL Server at all).
> > > > > > > >
> > > > > > > > If we continue going in this direction, we will end up with a
> > > > > product,
> > > > > > > > which is unsafe out of the box and require tons of
> > documentation
> > > to
> > > > > > > > understand how to make it safe. Definitely not the right
> > message
> > > to
> > > > > the
> > > > > > > > market. This is like a car without brakes - would you like to
> > > drive
> > > > > it?
> > > > > > > If
> > > > > > > > this is Need For Speed game and you have unlimited lives
> > > (in-memory
> > > > > > cache
> > > > > > > > with backing store), then yes. If this is a real life with
> > > > > > (persistence)
> > > > > > > -
> > > > > > > > then no.
> > > > > > > >
> > > > > > > > On Fri, Feb 16, 2018 at 5:20 PM, Dmitriy Setrakyan <
> > > > > > > [hidden email]>
> > > > > > > > wrote:
> > > > > > > >
> > > > > > > > > Well, I cannot say that I like the name LOG_ONLY, but I
> would
> > > > vote
> > > > > to
> > > > > > > > keep
> > > > > > > > > it for now, given that it is already documented in many
> > places,
> > > > > > blogs,
> > > > > > > > and
> > > > > > > > > examples.
> > > > > > > > >
> > > > > > > > > D.
> > > > > > > > >
> > > > > > > > > On Fri, Feb 16, 2018 at 8:13 AM, Ivan Rakov <
> > > > [hidden email]
> > > > > >
> > > > > > > > wrote:
> > > > > > > > >
> > > > > > > > > > Looks like it's an Ignite term - I've never heard of it
> > > outside
> > > > > > > Ignite
> > > > > > > > > > scope.
> > > > > > > > > >
> > > > > > > > > > Though, renaming existing enum value requires keeping old
> > as
> > > > > > > > deprecated.
> > > > > > > > > > DEFAULT is confusing enough to pay this price.
> > > > > > > > > > As for LOG_ONLY, I think we can keep it as long as it has
> > > good
> > > > > and
> > > > > > > > > > definitive javadoc.
> > > > > > > > > >
> > > > > > > > > > Best Regards,
> > > > > > > > > > Ivan Rakov
> > > > > > > > > >
> > > > > > > > > >
> > > > > > > > > > On 16.02.2018 17:07, Dmitriy Setrakyan wrote:
> > > > > > > > > >
> > > > > > > > > >> Igniters, just to clarify, does the term LOG_ONLY mean
> > > > anything
> > > > > in
> > > > > > > the
> > > > > > > > > >> industry or is this just an Ignite term?
> > > > > > > > > >>
> > > > > > > > > >> D.
> > > > > > > > > >>
> > > > > > > > > >> On Fri, Feb 16, 2018 at 8:03 AM, Anton Vinogradov <
> > > > > > > > > >> [hidden email]>
> > > > > > > > > >> wrote:
> > > > > > > > > >>
> > > > > > > > > >> Log only mode: flushes application buffers.
> > > > > > > > > >>> So, in synced mode without fsync guarantee. That's why
> I
> > > > > propose
> > > > > > to
> > > > > > > > > >>> rename
> > > > > > > > > >>> it as SYNC.
> > > > > > > > > >>>
> > > > > > > > > >>> On Fri, Feb 16, 2018 at 4:49 PM, Ilya Lantukh <
> > > > > > > [hidden email]
> > > > > > > > >
> > > > > > > > > >>> wrote:
> > > > > > > > > >>>
> > > > > > > > > >>> I am OK with either FSYNC or STRICT variant.
> > > > > > > > > >>>>
> > > > > > > > > >>>> LOG_ONLY name means "log without fsync".
> > > > > > > > > >>>>
> > > > > > > > > >>>> On Fri, Feb 16, 2018 at 4:05 PM, Dmitriy Setrakyan <
> > > > > > > > > >>>>
> > > > > > > > > >>> [hidden email]>
> > > > > > > > > >>>
> > > > > > > > > >>>> wrote:
> > > > > > > > > >>>>
> > > > > > > > > >>>> On Fri, Feb 16, 2018 at 7:02 AM, Ivan Rakov <
> > > > > > > [hidden email]>
> > > > > > > > > >>>>>
> > > > > > > > > >>>> wrote:
> > > > > > > > > >>>>
> > > > > > > > > >>>>> Why create a new term to define something that has
> > > already
> > > > > been
> > > > > > > > > >>>>>>
> > > > > > > > > >>>>> defined?
> > > > > > > > > >>>>
> > > > > > > > > >>>>> That makes sense. I'm ok with FSYNC.
> > > > > > > > > >>>>>> Anton, I don't understand why we should rename
> > LOG_ONLY
> > > to
> > > > > > SYNC.
> > > > > > > > We
> > > > > > > > > >>>>>> started this discussion with bad naming of DEFAULT,
> > but
> > > > this
> > > > > > has
> > > > > > > > > >>>>>>
> > > > > > > > > >>>>> nothing
> > > > > > > > > >>>>
> > > > > > > > > >>>>> to
> > > > > > > > > >>>>>
> > > > > > > > > >>>>>> do with LOG_ONLY (even though it may be scientific -
> > but
> > > > > SYNC
> > > > > > > > sounds
> > > > > > > > > >>>>>> scientific as well).
> > > > > > > > > >>>>>>
> > > > > > > > > >>>>>> I agree with Ivan, we should not go wild with
> > renaming.
> > > > > > > However, I
> > > > > > > > > >>>>>
> > > > > > > > > >>>> would
> > > > > > > > > >>>
> > > > > > > > > >>>> like to find out what is the meaning behind the
> LOG_ONLY
> > > > name.
> > > > > > Can
> > > > > > > > > >>>>>
> > > > > > > > > >>>> someone
> > > > > > > > > >>>>
> > > > > > > > > >>>>> explain?
> > > > > > > > > >>>>>
> > > > > > > > > >>>>> D.
> > > > > > > > > >>>>>
> > > > > > > > > >>>>>
> > > > > > > > > >>>>
> > > > > > > > > >>>> --
> > > > > > > > > >>>> Best regards,
> > > > > > > > > >>>> Ilya
> > > > > > > > > >>>>
> > > > > > > > > >>>>
> > > > > > > > > >
> > > > > > > > >
> > > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > >
> > >
> >
>
>
>
> --
> Sergey Kozlov
> GridGain Systems
> www.gridgain.com
>

[dsetrakyan]

Vova,

I hear your concerns, but at the same time I know that one of the largest
banks in eastern Europe is using Ignite in LOG_ONLY mode with 3 backups to
move money. The rational is that the probability of failure of 4 servers at
hardware level at the same time is very low. However, if the JVM process
fails on any server, then it can be safely restarted without loosing data.
In my view, this is why LOG_ONLY mode makes sense as a default.

I still vote to change the default to LOG_ONLY, deprecate the DEFAULT name
altogether and add FSYNC mode instead.

D.

On Fri, Feb 16, 2018 at 4:05 PM, Vladimir Ozerov <[hidden email]>
wrote:

> Sergey,
>
> We do not have backups by default either, so essentially we are loosing
> data by default. Moreover, backups are less reliable option than fsync
> because a lot of users cannot afford putting servers into separate power
> circuits, so a single power failure may easily lead to poweroff of the
> whole cluster at once, so data is lost still. This is normal practice even
> for enterprise deployments (e.g. asynchronous replication).
>
> To make things even worse, we employ PRIMARY_SYNC mode by default! So even
> if you configured backups, you still may loose data due to a single node
> failure - just shutdown the PRIMARY after commit is confirmed to the client
> and your recent update will disappers.
>
> So this is what user should do to make himself safe:
> 1) Learn about WAL modes
> 2) Learn about backups
> 3) Learn about synchronization modes
> 4) Cross his fingers that he understood everything correctly and that there
> are no other hidden surprises in Ignite which could lead to data loss.
>
> Way to much for a product, claiming to be A*C*ID and persistent, don't you
> think so?
>
> Leaving deafult WAL mode with fsync resolves all these issues.
>
> Vladimir.
>
>
> On Fri, Feb 16, 2018 at 11:43 PM, Sergey Kozlov <[hidden email]>
> wrote:
>
> > I suppose some approaches used by classic databases makes no sense for
> > Ignite. FSYNC requirement for databases has the nature of single host
> > solution. If you have corrupted db files you have corrupted (lost) data.
> >
> > For Ignite the enough number of backups and the failure detecting logic
> can
> > provide the data consistency in term "cluster data consistency".
> >
> >
> >
> > On Fri, Feb 16, 2018 at 8:57 PM, Dmitry Pavlov <[hidden email]>
> > wrote:
> >
> > > Hi, all WAL modes except NONE protects from data consistency problem
> > > (B+Tree, pages, etc), which is why I suggest to avoid saying
> 'corrupted'
> > > about 'unapplied updates'.
> > >
> > > Log Only and Background may cause unapplied updates in case of
> OS/process
> > > failures.
> > >
> > > None mode IMO is not an option in case data consistency is needed.
> > >
> > > пт, 16 февр. 2018 г. в 20:49, Valentin Kulichenko <
> > > [hidden email]>:
> > >
> > > > Guys,
> > > >
> > > > While we're on this topic, what is the difference between BACKGROUND
> > and
> > > > NONE in terms of semantics and provided guarantees? To me it looks
> like
> > > > both guarantee to recover the state since last checkpoint and
> anything
> > > else
> > > > can potentially be lost, so from user perspective they are the same.
> > Am I
> > > > missing something here?
> > > >
> > > > Also there is the following in Javadoc for NONE: "If an Ignite node
> is
> > > > terminated in NONE mode abruptly, it is likely that the data stored
> on
> > > disk
> > > > is corrupted and work directory will need to be cleared for a node
> > > > restart.". If this is really the case, I'm not sure NONE makes sense
> at
> > > > all. Why would I enable persistence if I'm likely to clear the
> storage
> > on
> > > > restart?
> > > >
> > > > -Val
> > > >
> > > > On Fri, Feb 16, 2018 at 8:39 AM, Vladimir Ozerov <
> [hidden email]
> > >
> > > > wrote:
> > > >
> > > > > What is the reason to have DEFAULT mode at all if you claim
> LOG_ONLY
> > to
> > > > be
> > > > > completely safe? :)
> > > > >
> > > > > And how it could be safe provided that without fsync we loose part
> of
> > > WAL
> > > > > itself in case of crash?
> > > > >
> > > > > пт, 16 февр. 2018 г. в 19:32, Dmitry Pavlov <[hidden email]
> >:
> > > > >
> > > > > > Thank you. Data can't be corrupted in case crash because of WAL
> > > replay
> > > > > > (since completed checkpoint). Physical records are used to
> restore
> > > > > probably
> > > > > > corrupted pages in persistent store (we overwrite so called 'grey
> > > > zone' -
> > > > > > pages we don't know for sure if they have been written).
> > > > > >
> > > > > > Only one effect is unwritten one or several last transactions. It
> > is
> > > > not
> > > > > > the same with corrupted data.
> > > > > >
> > > > > > пт, 16 февр. 2018 г. в 19:19, Vladimir Ozerov <
> > [hidden email]
> > > >:
> > > > > >
> > > > > > > Log only mode is not safe - data might be corrupted in case of
> > > system
> > > > > > > crash. Oracle - fsync, Postgres - fsync, SQL Server - fsync,
> > > > Cassandra
> > > > > -
> > > > > > > similar to our “background”.
> > > > > > >
> > > > > > > пт, 16 февр. 2018 г. в 19:11, Dmitry Pavlov <
> > [hidden email]
> > > >:
> > > > > > >
> > > > > > > > Hi Vladimir,
> > > > > > > >
> > > > > > > > What you saying is defenetely make sence.
> > > > > > > >
> > > > > > > > In the same time LOG_ONLY is also safe mode, user will be
> able
> > to
> > > > > > restore
> > > > > > > > system after crash. If it is not true, we should create
> > critical
> > > > > ticket
> > > > > > > and
> > > > > > > > fix it.
> > > > > > > >
> > > > > > > > Do you know other databases defaults, such as Cassandra,
> > Oracle,
> > > > > > Postgre?
> > > > > > > >
> > > > > > > > Sincerely,
> > > > > > > > Dmitriy Pavlov
> > > > > > > >
> > > > > > > > пт, 16 февр. 2018 г. в 18:41, Vladimir Ozerov <
> > > > [hidden email]
> > > > > >:
> > > > > > > >
> > > > > > > > > Igniters,
> > > > > > > > >
> > > > > > > > > Sorry for pouring oil on the flames, but from database
> > > > perspective
> > > > > > > moving
> > > > > > > > > from FSYNC to non-FSYNC mode appears to be a mistake. When
> > you
> > > > work
> > > > > > > with
> > > > > > > > > database, your main expectation is that it will save your
> > data.
> > > > All
> > > > > > > > > production database vendor make sure that you are safe, not
> > > that
> > > > > you
> > > > > > > are
> > > > > > > > > fast. Moreover, some vendors even prevent you from being in
> > > > unsafe
> > > > > > mode
> > > > > > > > > (e.g. you cannot disable fsync in SQL Server at all).
> > > > > > > > >
> > > > > > > > > If we continue going in this direction, we will end up
> with a
> > > > > > product,
> > > > > > > > > which is unsafe out of the box and require tons of
> > > documentation
> > > > to
> > > > > > > > > understand how to make it safe. Definitely not the right
> > > message
> > > > to
> > > > > > the
> > > > > > > > > market. This is like a car without brakes - would you like
> to
> > > > drive
> > > > > > it?
> > > > > > > > If
> > > > > > > > > this is Need For Speed game and you have unlimited lives
> > > > (in-memory
> > > > > > > cache
> > > > > > > > > with backing store), then yes. If this is a real life with
> > > > > > > (persistence)
> > > > > > > > -
> > > > > > > > > then no.
> > > > > > > > >
> > > > > > > > > On Fri, Feb 16, 2018 at 5:20 PM, Dmitriy Setrakyan <
> > > > > > > > [hidden email]>
> > > > > > > > > wrote:
> > > > > > > > >
> > > > > > > > > > Well, I cannot say that I like the name LOG_ONLY, but I
> > would
> > > > > vote
> > > > > > to
> > > > > > > > > keep
> > > > > > > > > > it for now, given that it is already documented in many
> > > places,
> > > > > > > blogs,
> > > > > > > > > and
> > > > > > > > > > examples.
> > > > > > > > > >
> > > > > > > > > > D.
> > > > > > > > > >
> > > > > > > > > > On Fri, Feb 16, 2018 at 8:13 AM, Ivan Rakov <
> > > > > [hidden email]
> > > > > > >
> > > > > > > > > wrote:
> > > > > > > > > >
> > > > > > > > > > > Looks like it's an Ignite term - I've never heard of it
> > > > outside
> > > > > > > > Ignite
> > > > > > > > > > > scope.
> > > > > > > > > > >
> > > > > > > > > > > Though, renaming existing enum value requires keeping
> old
> > > as
> > > > > > > > > deprecated.
> > > > > > > > > > > DEFAULT is confusing enough to pay this price.
> > > > > > > > > > > As for LOG_ONLY, I think we can keep it as long as it
> has
> > > > good
> > > > > > and
> > > > > > > > > > > definitive javadoc.
> > > > > > > > > > >
> > > > > > > > > > > Best Regards,
> > > > > > > > > > > Ivan Rakov
> > > > > > > > > > >
> > > > > > > > > > >
> > > > > > > > > > > On 16.02.2018 17:07, Dmitriy Setrakyan wrote:
> > > > > > > > > > >
> > > > > > > > > > >> Igniters, just to clarify, does the term LOG_ONLY mean
> > > > > anything
> > > > > > in
> > > > > > > > the
> > > > > > > > > > >> industry or is this just an Ignite term?
> > > > > > > > > > >>
> > > > > > > > > > >> D.
> > > > > > > > > > >>
> > > > > > > > > > >> On Fri, Feb 16, 2018 at 8:03 AM, Anton Vinogradov <
> > > > > > > > > > >> [hidden email]>
> > > > > > > > > > >> wrote:
> > > > > > > > > > >>
> > > > > > > > > > >> Log only mode: flushes application buffers.
> > > > > > > > > > >>> So, in synced mode without fsync guarantee. That's
> why
> > I
> > > > > > propose
> > > > > > > to
> > > > > > > > > > >>> rename
> > > > > > > > > > >>> it as SYNC.
> > > > > > > > > > >>>
> > > > > > > > > > >>> On Fri, Feb 16, 2018 at 4:49 PM, Ilya Lantukh <
> > > > > > > > [hidden email]
> > > > > > > > > >
> > > > > > > > > > >>> wrote:
> > > > > > > > > > >>>
> > > > > > > > > > >>> I am OK with either FSYNC or STRICT variant.
> > > > > > > > > > >>>>
> > > > > > > > > > >>>> LOG_ONLY name means "log without fsync".
> > > > > > > > > > >>>>
> > > > > > > > > > >>>> On Fri, Feb 16, 2018 at 4:05 PM, Dmitriy Setrakyan <
> > > > > > > > > > >>>>
> > > > > > > > > > >>> [hidden email]>
> > > > > > > > > > >>>
> > > > > > > > > > >>>> wrote:
> > > > > > > > > > >>>>
> > > > > > > > > > >>>> On Fri, Feb 16, 2018 at 7:02 AM, Ivan Rakov <
> > > > > > > > [hidden email]>
> > > > > > > > > > >>>>>
> > > > > > > > > > >>>> wrote:
> > > > > > > > > > >>>>
> > > > > > > > > > >>>>> Why create a new term to define something that has
> > > > already
> > > > > > been
> > > > > > > > > > >>>>>>
> > > > > > > > > > >>>>> defined?
> > > > > > > > > > >>>>
> > > > > > > > > > >>>>> That makes sense. I'm ok with FSYNC.
> > > > > > > > > > >>>>>> Anton, I don't understand why we should rename
> > > LOG_ONLY
> > > > to
> > > > > > > SYNC.
> > > > > > > > > We
> > > > > > > > > > >>>>>> started this discussion with bad naming of
> DEFAULT,
> > > but
> > > > > this
> > > > > > > has
> > > > > > > > > > >>>>>>
> > > > > > > > > > >>>>> nothing
> > > > > > > > > > >>>>
> > > > > > > > > > >>>>> to
> > > > > > > > > > >>>>>
> > > > > > > > > > >>>>>> do with LOG_ONLY (even though it may be
> scientific -
> > > but
> > > > > > SYNC
> > > > > > > > > sounds
> > > > > > > > > > >>>>>> scientific as well).
> > > > > > > > > > >>>>>>
> > > > > > > > > > >>>>>> I agree with Ivan, we should not go wild with
> > > renaming.
> > > > > > > > However, I
> > > > > > > > > > >>>>>
> > > > > > > > > > >>>> would
> > > > > > > > > > >>>
> > > > > > > > > > >>>> like to find out what is the meaning behind the
> > LOG_ONLY
> > > > > name.
> > > > > > > Can
> > > > > > > > > > >>>>>
> > > > > > > > > > >>>> someone
> > > > > > > > > > >>>>
> > > > > > > > > > >>>>> explain?
> > > > > > > > > > >>>>>
> > > > > > > > > > >>>>> D.
> > > > > > > > > > >>>>>
> > > > > > > > > > >>>>>
> > > > > > > > > > >>>>
> > > > > > > > > > >>>> --
> > > > > > > > > > >>>> Best regards,
> > > > > > > > > > >>>> Ilya
> > > > > > > > > > >>>>
> > > > > > > > > > >>>>
> > > > > > > > > > >
> > > > > > > > > >
> > > > > > > > >
> > > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > >
> > >
> >
> >
> >
> > --
> > Sergey Kozlov
> > GridGain Systems
> > www.gridgain.com
> >
>

[dmagda]

Classic relational databases have no choice rather than to use FSYNC by
default. RDBMS is all about consistency.

Distributed databases try to balance consistency and performance. For
instance, why to fsync every update if there is usually 1 backup copy?
This is probably why VoltDB [1] and Cassandra use the modes comparable to
Ignite's LOG_ONLY.

Ignite as a distributed database should care of both consistency and
performance.

My vote goes to FSYNC, LOG_ONLY (default), BACKGROUND, NONE.


[1] https://docs.voltdb.com/UsingVoltDB/CmdLogConfig.php

--
Denis


On Fri, Feb 16, 2018 at 2:14 PM, Dmitriy Setrakyan <[hidden email]>
wrote:

> Vova,
>
> I hear your concerns, but at the same time I know that one of the largest
> banks in eastern Europe is using Ignite in LOG_ONLY mode with 3 backups to
> move money. The rational is that the probability of failure of 4 servers at
> hardware level at the same time is very low. However, if the JVM process
> fails on any server, then it can be safely restarted without loosing data.
> In my view, this is why LOG_ONLY mode makes sense as a default.
>
> I still vote to change the default to LOG_ONLY, deprecate the DEFAULT name
> altogether and add FSYNC mode instead.
>
> D.
>
> On Fri, Feb 16, 2018 at 4:05 PM, Vladimir Ozerov <[hidden email]>
> wrote:
>
> > Sergey,
> >
> > We do not have backups by default either, so essentially we are loosing
> > data by default. Moreover, backups are less reliable option than fsync
> > because a lot of users cannot afford putting servers into separate power
> > circuits, so a single power failure may easily lead to poweroff of the
> > whole cluster at once, so data is lost still. This is normal practice
> even
> > for enterprise deployments (e.g. asynchronous replication).
> >
> > To make things even worse, we employ PRIMARY_SYNC mode by default! So
> even
> > if you configured backups, you still may loose data due to a single node
> > failure - just shutdown the PRIMARY after commit is confirmed to the
> client
> > and your recent update will disappers.
> >
> > So this is what user should do to make himself safe:
> > 1) Learn about WAL modes
> > 2) Learn about backups
> > 3) Learn about synchronization modes
> > 4) Cross his fingers that he understood everything correctly and that
> there
> > are no other hidden surprises in Ignite which could lead to data loss.
> >
> > Way to much for a product, claiming to be A*C*ID and persistent, don't
> you
> > think so?
> >
> > Leaving deafult WAL mode with fsync resolves all these issues.
> >
> > Vladimir.
> >
> >
> > On Fri, Feb 16, 2018 at 11:43 PM, Sergey Kozlov <[hidden email]>
> > wrote:
> >
> > > I suppose some approaches used by classic databases makes no sense for
> > > Ignite. FSYNC requirement for databases has the nature of single host
> > > solution. If you have corrupted db files you have corrupted (lost)
> data.
> > >
> > > For Ignite the enough number of backups and the failure detecting logic
> > can
> > > provide the data consistency in term "cluster data consistency".
> > >
> > >
> > >
> > > On Fri, Feb 16, 2018 at 8:57 PM, Dmitry Pavlov <[hidden email]>
> > > wrote:
> > >
> > > > Hi, all WAL modes except NONE protects from data consistency problem
> > > > (B+Tree, pages, etc), which is why I suggest to avoid saying
> > 'corrupted'
> > > > about 'unapplied updates'.
> > > >
> > > > Log Only and Background may cause unapplied updates in case of
> > OS/process
> > > > failures.
> > > >
> > > > None mode IMO is not an option in case data consistency is needed.
> > > >
> > > > пт, 16 февр. 2018 г. в 20:49, Valentin Kulichenko <
> > > > [hidden email]>:
> > > >
> > > > > Guys,
> > > > >
> > > > > While we're on this topic, what is the difference between
> BACKGROUND
> > > and
> > > > > NONE in terms of semantics and provided guarantees? To me it looks
> > like
> > > > > both guarantee to recover the state since last checkpoint and
> > anything
> > > > else
> > > > > can potentially be lost, so from user perspective they are the
> same.
> > > Am I
> > > > > missing something here?
> > > > >
> > > > > Also there is the following in Javadoc for NONE: "If an Ignite node
> > is
> > > > > terminated in NONE mode abruptly, it is likely that the data stored
> > on
> > > > disk
> > > > > is corrupted and work directory will need to be cleared for a node
> > > > > restart.". If this is really the case, I'm not sure NONE makes
> sense
> > at
> > > > > all. Why would I enable persistence if I'm likely to clear the
> > storage
> > > on
> > > > > restart?
> > > > >
> > > > > -Val
> > > > >
> > > > > On Fri, Feb 16, 2018 at 8:39 AM, Vladimir Ozerov <
> > [hidden email]
> > > >
> > > > > wrote:
> > > > >
> > > > > > What is the reason to have DEFAULT mode at all if you claim
> > LOG_ONLY
> > > to
> > > > > be
> > > > > > completely safe? :)
> > > > > >
> > > > > > And how it could be safe provided that without fsync we loose
> part
> > of
> > > > WAL
> > > > > > itself in case of crash?
> > > > > >
> > > > > > пт, 16 февр. 2018 г. в 19:32, Dmitry Pavlov <
> [hidden email]
> > >:
> > > > > >
> > > > > > > Thank you. Data can't be corrupted in case crash because of WAL
> > > > replay
> > > > > > > (since completed checkpoint). Physical records are used to
> > restore
> > > > > > probably
> > > > > > > corrupted pages in persistent store (we overwrite so called
> 'grey
> > > > > zone' -
> > > > > > > pages we don't know for sure if they have been written).
> > > > > > >
> > > > > > > Only one effect is unwritten one or several last transactions.
> It
> > > is
> > > > > not
> > > > > > > the same with corrupted data.
> > > > > > >
> > > > > > > пт, 16 февр. 2018 г. в 19:19, Vladimir Ozerov <
> > > [hidden email]
> > > > >:
> > > > > > >
> > > > > > > > Log only mode is not safe - data might be corrupted in case
> of
> > > > system
> > > > > > > > crash. Oracle - fsync, Postgres - fsync, SQL Server - fsync,
> > > > > Cassandra
> > > > > > -
> > > > > > > > similar to our “background”.
> > > > > > > >
> > > > > > > > пт, 16 февр. 2018 г. в 19:11, Dmitry Pavlov <
> > > [hidden email]
> > > > >:
> > > > > > > >
> > > > > > > > > Hi Vladimir,
> > > > > > > > >
> > > > > > > > > What you saying is defenetely make sence.
> > > > > > > > >
> > > > > > > > > In the same time LOG_ONLY is also safe mode, user will be
> > able
> > > to
> > > > > > > restore
> > > > > > > > > system after crash. If it is not true, we should create
> > > critical
> > > > > > ticket
> > > > > > > > and
> > > > > > > > > fix it.
> > > > > > > > >
> > > > > > > > > Do you know other databases defaults, such as Cassandra,
> > > Oracle,
> > > > > > > Postgre?
> > > > > > > > >
> > > > > > > > > Sincerely,
> > > > > > > > > Dmitriy Pavlov
> > > > > > > > >
> > > > > > > > > пт, 16 февр. 2018 г. в 18:41, Vladimir Ozerov <
> > > > > [hidden email]
> > > > > > >:
> > > > > > > > >
> > > > > > > > > > Igniters,
> > > > > > > > > >
> > > > > > > > > > Sorry for pouring oil on the flames, but from database
> > > > > perspective
> > > > > > > > moving
> > > > > > > > > > from FSYNC to non-FSYNC mode appears to be a mistake.
> When
> > > you
> > > > > work
> > > > > > > > with
> > > > > > > > > > database, your main expectation is that it will save your
> > > data.
> > > > > All
> > > > > > > > > > production database vendor make sure that you are safe,
> not
> > > > that
> > > > > > you
> > > > > > > > are
> > > > > > > > > > fast. Moreover, some vendors even prevent you from being
> in
> > > > > unsafe
> > > > > > > mode
> > > > > > > > > > (e.g. you cannot disable fsync in SQL Server at all).
> > > > > > > > > >
> > > > > > > > > > If we continue going in this direction, we will end up
> > with a
> > > > > > > product,
> > > > > > > > > > which is unsafe out of the box and require tons of
> > > > documentation
> > > > > to
> > > > > > > > > > understand how to make it safe. Definitely not the right
> > > > message
> > > > > to
> > > > > > > the
> > > > > > > > > > market. This is like a car without brakes - would you
> like
> > to
> > > > > drive
> > > > > > > it?
> > > > > > > > > If
> > > > > > > > > > this is Need For Speed game and you have unlimited lives
> > > > > (in-memory
> > > > > > > > cache
> > > > > > > > > > with backing store), then yes. If this is a real life
> with
> > > > > > > > (persistence)
> > > > > > > > > -
> > > > > > > > > > then no.
> > > > > > > > > >
> > > > > > > > > > On Fri, Feb 16, 2018 at 5:20 PM, Dmitriy Setrakyan <
> > > > > > > > > [hidden email]>
> > > > > > > > > > wrote:
> > > > > > > > > >
> > > > > > > > > > > Well, I cannot say that I like the name LOG_ONLY, but I
> > > would
> > > > > > vote
> > > > > > > to
> > > > > > > > > > keep
> > > > > > > > > > > it for now, given that it is already documented in many
> > > > places,
> > > > > > > > blogs,
> > > > > > > > > > and
> > > > > > > > > > > examples.
> > > > > > > > > > >
> > > > > > > > > > > D.
> > > > > > > > > > >
> > > > > > > > > > > On Fri, Feb 16, 2018 at 8:13 AM, Ivan Rakov <
> > > > > > [hidden email]
> > > > > > > >
> > > > > > > > > > wrote:
> > > > > > > > > > >
> > > > > > > > > > > > Looks like it's an Ignite term - I've never heard of
> it
> > > > > outside
> > > > > > > > > Ignite
> > > > > > > > > > > > scope.
> > > > > > > > > > > >
> > > > > > > > > > > > Though, renaming existing enum value requires keeping
> > old
> > > > as
> > > > > > > > > > deprecated.
> > > > > > > > > > > > DEFAULT is confusing enough to pay this price.
> > > > > > > > > > > > As for LOG_ONLY, I think we can keep it as long as it
> > has
> > > > > good
> > > > > > > and
> > > > > > > > > > > > definitive javadoc.
> > > > > > > > > > > >
> > > > > > > > > > > > Best Regards,
> > > > > > > > > > > > Ivan Rakov
> > > > > > > > > > > >
> > > > > > > > > > > >
> > > > > > > > > > > > On 16.02.2018 17:07, Dmitriy Setrakyan wrote:
> > > > > > > > > > > >
> > > > > > > > > > > >> Igniters, just to clarify, does the term LOG_ONLY
> mean
> > > > > > anything
> > > > > > > in
> > > > > > > > > the
> > > > > > > > > > > >> industry or is this just an Ignite term?
> > > > > > > > > > > >>
> > > > > > > > > > > >> D.
> > > > > > > > > > > >>
> > > > > > > > > > > >> On Fri, Feb 16, 2018 at 8:03 AM, Anton Vinogradov <
> > > > > > > > > > > >> [hidden email]>
> > > > > > > > > > > >> wrote:
> > > > > > > > > > > >>
> > > > > > > > > > > >> Log only mode: flushes application buffers.
> > > > > > > > > > > >>> So, in synced mode without fsync guarantee. That's
> > why
> > > I
> > > > > > > propose
> > > > > > > > to
> > > > > > > > > > > >>> rename
> > > > > > > > > > > >>> it as SYNC.
> > > > > > > > > > > >>>
> > > > > > > > > > > >>> On Fri, Feb 16, 2018 at 4:49 PM, Ilya Lantukh <
> > > > > > > > > [hidden email]
> > > > > > > > > > >
> > > > > > > > > > > >>> wrote:
> > > > > > > > > > > >>>
> > > > > > > > > > > >>> I am OK with either FSYNC or STRICT variant.
> > > > > > > > > > > >>>>
> > > > > > > > > > > >>>> LOG_ONLY name means "log without fsync".
> > > > > > > > > > > >>>>
> > > > > > > > > > > >>>> On Fri, Feb 16, 2018 at 4:05 PM, Dmitriy
> Setrakyan <
> > > > > > > > > > > >>>>
> > > > > > > > > > > >>> [hidden email]>
> > > > > > > > > > > >>>
> > > > > > > > > > > >>>> wrote:
> > > > > > > > > > > >>>>
> > > > > > > > > > > >>>> On Fri, Feb 16, 2018 at 7:02 AM, Ivan Rakov <
> > > > > > > > > [hidden email]>
> > > > > > > > > > > >>>>>
> > > > > > > > > > > >>>> wrote:
> > > > > > > > > > > >>>>
> > > > > > > > > > > >>>>> Why create a new term to define something that
> has
> > > > > already
> > > > > > > been
> > > > > > > > > > > >>>>>>
> > > > > > > > > > > >>>>> defined?
> > > > > > > > > > > >>>>
> > > > > > > > > > > >>>>> That makes sense. I'm ok with FSYNC.
> > > > > > > > > > > >>>>>> Anton, I don't understand why we should rename
> > > > LOG_ONLY
> > > > > to
> > > > > > > > SYNC.
> > > > > > > > > > We
> > > > > > > > > > > >>>>>> started this discussion with bad naming of
> > DEFAULT,
> > > > but
> > > > > > this
> > > > > > > > has
> > > > > > > > > > > >>>>>>
> > > > > > > > > > > >>>>> nothing
> > > > > > > > > > > >>>>
> > > > > > > > > > > >>>>> to
> > > > > > > > > > > >>>>>
> > > > > > > > > > > >>>>>> do with LOG_ONLY (even though it may be
> > scientific -
> > > > but
> > > > > > > SYNC
> > > > > > > > > > sounds
> > > > > > > > > > > >>>>>> scientific as well).
> > > > > > > > > > > >>>>>>
> > > > > > > > > > > >>>>>> I agree with Ivan, we should not go wild with
> > > > renaming.
> > > > > > > > > However, I
> > > > > > > > > > > >>>>>
> > > > > > > > > > > >>>> would
> > > > > > > > > > > >>>
> > > > > > > > > > > >>>> like to find out what is the meaning behind the
> > > LOG_ONLY
> > > > > > name.
> > > > > > > > Can
> > > > > > > > > > > >>>>>
> > > > > > > > > > > >>>> someone
> > > > > > > > > > > >>>>
> > > > > > > > > > > >>>>> explain?
> > > > > > > > > > > >>>>>
> > > > > > > > > > > >>>>> D.
> > > > > > > > > > > >>>>>
> > > > > > > > > > > >>>>>
> > > > > > > > > > > >>>>
> > > > > > > > > > > >>>> --
> > > > > > > > > > > >>>> Best regards,
> > > > > > > > > > > >>>> Ilya
> > > > > > > > > > > >>>>
> > > > > > > > > > > >>>>
> > > > > > > > > > > >
> > > > > > > > > > >
> > > > > > > > > >
> > > > > > > > >
> > > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > >
> > >
> > >
> > >
> > > --
> > > Sergey Kozlov
> > > GridGain Systems
> > > www.gridgain.com
> > >
> >
>

[Alexey Goncharuk]

In terms of 'safety', Ignite default settings are far beyond optimal. For
in-memory mode, we have 0 backups by default, which means partition loss in
a case of node failure, we have readFromBackup=true and PRIMARY_SYNC by
default which effectively cancels linearizability property for cache
updates, so setting the default WAL mode to LOG_ONLY does not seem to be a
bigger evil than it currently is. If we are to move to safer defaults, we
should change all of the affected sides.

I also want to clarify the difference between guarantees in
non-fsync modes. We should distinguish the loss of durability (the loss of
the last update) because the update did not make it to disk and data loss
because the disk content was shuffled due to an incomplete page write. In
my understanding, the current situation is:
FSYNC: loss of durability: not possible, data loss: not possible
LOG_ONLY: loss of durability: possible only if OS/power fails, data loss:
possible only if OS/power fails
BACKGROUND: loss of durability: possible if Ignite process fails, data
loss: possible only if OS/power fails

The data loss situation can be mitigated in the cluster using a large
enough replication factor (this is what Dmitriy was describing in the case
of LOG_ONLY and 3 backups configuration).

Denis,
I do not think it is fair to compare Ignite defaults to Cassandra's
defaults because Cassandra is _not_ transactional _eventually consistent_
datastore, they claim much weaker guarantees than Ignite.

All in all, I'm ok to change the WAL default right now, but I would revisit
all those settings in 3.0 and made Ignite safe-first.

2018-02-17 3:24 GMT+03:00 Denis Magda <[hidden email]>:

> Classic relational databases have no choice rather than to use FSYNC by
> default. RDBMS is all about consistency.
>
> Distributed databases try to balance consistency and performance. For
> instance, why to fsync every update if there is usually 1 backup copy?
> This is probably why VoltDB [1] and Cassandra use the modes comparable to
> Ignite's LOG_ONLY.
>
> Ignite as a distributed database should care of both consistency and
> performance.
>
> My vote goes to FSYNC, LOG_ONLY (default), BACKGROUND, NONE.
>
>
> [1] https://docs.voltdb.com/UsingVoltDB/CmdLogConfig.php
>
> --
> Denis
>
>
> On Fri, Feb 16, 2018 at 2:14 PM, Dmitriy Setrakyan <[hidden email]>
> wrote:
>
> > Vova,
> >
> > I hear your concerns, but at the same time I know that one of the largest
> > banks in eastern Europe is using Ignite in LOG_ONLY mode with 3 backups
> to
> > move money. The rational is that the probability of failure of 4 servers
> at
> > hardware level at the same time is very low. However, if the JVM process
> > fails on any server, then it can be safely restarted without loosing
> data.
> > In my view, this is why LOG_ONLY mode makes sense as a default.
> >
> > I still vote to change the default to LOG_ONLY, deprecate the DEFAULT
> name
> > altogether and add FSYNC mode instead.
> >
> > D.
> >
> > On Fri, Feb 16, 2018 at 4:05 PM, Vladimir Ozerov <[hidden email]>
> > wrote:
> >
> > > Sergey,
> > >
> > > We do not have backups by default either, so essentially we are loosing
> > > data by default. Moreover, backups are less reliable option than fsync
> > > because a lot of users cannot afford putting servers into separate
> power
> > > circuits, so a single power failure may easily lead to poweroff of the
> > > whole cluster at once, so data is lost still. This is normal practice
> > even
> > > for enterprise deployments (e.g. asynchronous replication).
> > >
> > > To make things even worse, we employ PRIMARY_SYNC mode by default! So
> > even
> > > if you configured backups, you still may loose data due to a single
> node
> > > failure - just shutdown the PRIMARY after commit is confirmed to the
> > client
> > > and your recent update will disappers.
> > >
> > > So this is what user should do to make himself safe:
> > > 1) Learn about WAL modes
> > > 2) Learn about backups
> > > 3) Learn about synchronization modes
> > > 4) Cross his fingers that he understood everything correctly and that
> > there
> > > are no other hidden surprises in Ignite which could lead to data loss.
> > >
> > > Way to much for a product, claiming to be A*C*ID and persistent, don't
> > you
> > > think so?
> > >
> > > Leaving deafult WAL mode with fsync resolves all these issues.
> > >
> > > Vladimir.
> > >
> > >
> > > On Fri, Feb 16, 2018 at 11:43 PM, Sergey Kozlov <[hidden email]>
> > > wrote:
> > >
> > > > I suppose some approaches used by classic databases makes no sense
> for
> > > > Ignite. FSYNC requirement for databases has the nature of single host
> > > > solution. If you have corrupted db files you have corrupted (lost)
> > data.
> > > >
> > > > For Ignite the enough number of backups and the failure detecting
> logic
> > > can
> > > > provide the data consistency in term "cluster data consistency".
> > > >
> > > >
> > > >
> > > > On Fri, Feb 16, 2018 at 8:57 PM, Dmitry Pavlov <
> [hidden email]>
> > > > wrote:
> > > >
> > > > > Hi, all WAL modes except NONE protects from data consistency
> problem
> > > > > (B+Tree, pages, etc), which is why I suggest to avoid saying
> > > 'corrupted'
> > > > > about 'unapplied updates'.
> > > > >
> > > > > Log Only and Background may cause unapplied updates in case of
> > > OS/process
> > > > > failures.
> > > > >
> > > > > None mode IMO is not an option in case data consistency is needed.
> > > > >
> > > > > пт, 16 февр. 2018 г. в 20:49, Valentin Kulichenko <
> > > > > [hidden email]>:
> > > > >
> > > > > > Guys,
> > > > > >
> > > > > > While we're on this topic, what is the difference between
> > BACKGROUND
> > > > and
> > > > > > NONE in terms of semantics and provided guarantees? To me it
> looks
> > > like
> > > > > > both guarantee to recover the state since last checkpoint and
> > > anything
> > > > > else
> > > > > > can potentially be lost, so from user perspective they are the
> > same.
> > > > Am I
> > > > > > missing something here?
> > > > > >
> > > > > > Also there is the following in Javadoc for NONE: "If an Ignite
> node
> > > is
> > > > > > terminated in NONE mode abruptly, it is likely that the data
> stored
> > > on
> > > > > disk
> > > > > > is corrupted and work directory will need to be cleared for a
> node
> > > > > > restart.". If this is really the case, I'm not sure NONE makes
> > sense
> > > at
> > > > > > all. Why would I enable persistence if I'm likely to clear the
> > > storage
> > > > on
> > > > > > restart?
> > > > > >
> > > > > > -Val
> > > > > >
> > > > > > On Fri, Feb 16, 2018 at 8:39 AM, Vladimir Ozerov <
> > > [hidden email]
> > > > >
> > > > > > wrote:
> > > > > >
> > > > > > > What is the reason to have DEFAULT mode at all if you claim
> > > LOG_ONLY
> > > > to
> > > > > > be
> > > > > > > completely safe? :)
> > > > > > >
> > > > > > > And how it could be safe provided that without fsync we loose
> > part
> > > of
> > > > > WAL
> > > > > > > itself in case of crash?
> > > > > > >
> > > > > > > пт, 16 февр. 2018 г. в 19:32, Dmitry Pavlov <
> > [hidden email]
> > > >:
> > > > > > >
> > > > > > > > Thank you. Data can't be corrupted in case crash because of
> WAL
> > > > > replay
> > > > > > > > (since completed checkpoint). Physical records are used to
> > > restore
> > > > > > > probably
> > > > > > > > corrupted pages in persistent store (we overwrite so called
> > 'grey
> > > > > > zone' -
> > > > > > > > pages we don't know for sure if they have been written).
> > > > > > > >
> > > > > > > > Only one effect is unwritten one or several last
> transactions.
> > It
> > > > is
> > > > > > not
> > > > > > > > the same with corrupted data.
> > > > > > > >
> > > > > > > > пт, 16 февр. 2018 г. в 19:19, Vladimir Ozerov <
> > > > [hidden email]
> > > > > >:
> > > > > > > >
> > > > > > > > > Log only mode is not safe - data might be corrupted in case
> > of
> > > > > system
> > > > > > > > > crash. Oracle - fsync, Postgres - fsync, SQL Server -
> fsync,
> > > > > > Cassandra
> > > > > > > -
> > > > > > > > > similar to our “background”.
> > > > > > > > >
> > > > > > > > > пт, 16 февр. 2018 г. в 19:11, Dmitry Pavlov <
> > > > [hidden email]
> > > > > >:
> > > > > > > > >
> > > > > > > > > > Hi Vladimir,
> > > > > > > > > >
> > > > > > > > > > What you saying is defenetely make sence.
> > > > > > > > > >
> > > > > > > > > > In the same time LOG_ONLY is also safe mode, user will be
> > > able
> > > > to
> > > > > > > > restore
> > > > > > > > > > system after crash. If it is not true, we should create
> > > > critical
> > > > > > > ticket
> > > > > > > > > and
> > > > > > > > > > fix it.
> > > > > > > > > >
> > > > > > > > > > Do you know other databases defaults, such as Cassandra,
> > > > Oracle,
> > > > > > > > Postgre?
> > > > > > > > > >
> > > > > > > > > > Sincerely,
> > > > > > > > > > Dmitriy Pavlov
> > > > > > > > > >
> > > > > > > > > > пт, 16 февр. 2018 г. в 18:41, Vladimir Ozerov <
> > > > > > [hidden email]
> > > > > > > >:
> > > > > > > > > >
> > > > > > > > > > > Igniters,
> > > > > > > > > > >
> > > > > > > > > > > Sorry for pouring oil on the flames, but from database
> > > > > > perspective
> > > > > > > > > moving
> > > > > > > > > > > from FSYNC to non-FSYNC mode appears to be a mistake.
> > When
> > > > you
> > > > > > work
> > > > > > > > > with
> > > > > > > > > > > database, your main expectation is that it will save
> your
> > > > data.
> > > > > > All
> > > > > > > > > > > production database vendor make sure that you are safe,
> > not
> > > > > that
> > > > > > > you
> > > > > > > > > are
> > > > > > > > > > > fast. Moreover, some vendors even prevent you from
> being
> > in
> > > > > > unsafe
> > > > > > > > mode
> > > > > > > > > > > (e.g. you cannot disable fsync in SQL Server at all).
> > > > > > > > > > >
> > > > > > > > > > > If we continue going in this direction, we will end up
> > > with a
> > > > > > > > product,
> > > > > > > > > > > which is unsafe out of the box and require tons of
> > > > > documentation
> > > > > > to
> > > > > > > > > > > understand how to make it safe. Definitely not the
> right
> > > > > message
> > > > > > to
> > > > > > > > the
> > > > > > > > > > > market. This is like a car without brakes - would you
> > like
> > > to
> > > > > > drive
> > > > > > > > it?
> > > > > > > > > > If
> > > > > > > > > > > this is Need For Speed game and you have unlimited
> lives
> > > > > > (in-memory
> > > > > > > > > cache
> > > > > > > > > > > with backing store), then yes. If this is a real life
> > with
> > > > > > > > > (persistence)
> > > > > > > > > > -
> > > > > > > > > > > then no.
> > > > > > > > > > >
> > > > > > > > > > > On Fri, Feb 16, 2018 at 5:20 PM, Dmitriy Setrakyan <
> > > > > > > > > > [hidden email]>
> > > > > > > > > > > wrote:
> > > > > > > > > > >
> > > > > > > > > > > > Well, I cannot say that I like the name LOG_ONLY,
> but I
> > > > would
> > > > > > > vote
> > > > > > > > to
> > > > > > > > > > > keep
> > > > > > > > > > > > it for now, given that it is already documented in
> many
> > > > > places,
> > > > > > > > > blogs,
> > > > > > > > > > > and
> > > > > > > > > > > > examples.
> > > > > > > > > > > >
> > > > > > > > > > > > D.
> > > > > > > > > > > >
> > > > > > > > > > > > On Fri, Feb 16, 2018 at 8:13 AM, Ivan Rakov <
> > > > > > > [hidden email]
> > > > > > > > >
> > > > > > > > > > > wrote:
> > > > > > > > > > > >
> > > > > > > > > > > > > Looks like it's an Ignite term - I've never heard
> of
> > it
> > > > > > outside
> > > > > > > > > > Ignite
> > > > > > > > > > > > > scope.
> > > > > > > > > > > > >
> > > > > > > > > > > > > Though, renaming existing enum value requires
> keeping
> > > old
> > > > > as
> > > > > > > > > > > deprecated.
> > > > > > > > > > > > > DEFAULT is confusing enough to pay this price.
> > > > > > > > > > > > > As for LOG_ONLY, I think we can keep it as long as
> it
> > > has
> > > > > > good
> > > > > > > > and
> > > > > > > > > > > > > definitive javadoc.
> > > > > > > > > > > > >
> > > > > > > > > > > > > Best Regards,
> > > > > > > > > > > > > Ivan Rakov
> > > > > > > > > > > > >
> > > > > > > > > > > > >
> > > > > > > > > > > > > On 16.02.2018 17:07, Dmitriy Setrakyan wrote:
> > > > > > > > > > > > >
> > > > > > > > > > > > >> Igniters, just to clarify, does the term LOG_ONLY
> > mean
> > > > > > > anything
> > > > > > > > in
> > > > > > > > > > the
> > > > > > > > > > > > >> industry or is this just an Ignite term?
> > > > > > > > > > > > >>
> > > > > > > > > > > > >> D.
> > > > > > > > > > > > >>
> > > > > > > > > > > > >> On Fri, Feb 16, 2018 at 8:03 AM, Anton Vinogradov
> <
> > > > > > > > > > > > >> [hidden email]>
> > > > > > > > > > > > >> wrote:
> > > > > > > > > > > > >>
> > > > > > > > > > > > >> Log only mode: flushes application buffers.
> > > > > > > > > > > > >>> So, in synced mode without fsync guarantee.
> That's
> > > why
> > > > I
> > > > > > > > propose
> > > > > > > > > to
> > > > > > > > > > > > >>> rename
> > > > > > > > > > > > >>> it as SYNC.
> > > > > > > > > > > > >>>
> > > > > > > > > > > > >>> On Fri, Feb 16, 2018 at 4:49 PM, Ilya Lantukh <
> > > > > > > > > > [hidden email]
> > > > > > > > > > > >
> > > > > > > > > > > > >>> wrote:
> > > > > > > > > > > > >>>
> > > > > > > > > > > > >>> I am OK with either FSYNC or STRICT variant.
> > > > > > > > > > > > >>>>
> > > > > > > > > > > > >>>> LOG_ONLY name means "log without fsync".
> > > > > > > > > > > > >>>>
> > > > > > > > > > > > >>>> On Fri, Feb 16, 2018 at 4:05 PM, Dmitriy
> > Setrakyan <
> > > > > > > > > > > > >>>>
> > > > > > > > > > > > >>> [hidden email]>
> > > > > > > > > > > > >>>
> > > > > > > > > > > > >>>> wrote:
> > > > > > > > > > > > >>>>
> > > > > > > > > > > > >>>> On Fri, Feb 16, 2018 at 7:02 AM, Ivan Rakov <
> > > > > > > > > > [hidden email]>
> > > > > > > > > > > > >>>>>
> > > > > > > > > > > > >>>> wrote:
> > > > > > > > > > > > >>>>
> > > > > > > > > > > > >>>>> Why create a new term to define something that
> > has
> > > > > > already
> > > > > > > > been
> > > > > > > > > > > > >>>>>>
> > > > > > > > > > > > >>>>> defined?
> > > > > > > > > > > > >>>>
> > > > > > > > > > > > >>>>> That makes sense. I'm ok with FSYNC.
> > > > > > > > > > > > >>>>>> Anton, I don't understand why we should rename
> > > > > LOG_ONLY
> > > > > > to
> > > > > > > > > SYNC.
> > > > > > > > > > > We
> > > > > > > > > > > > >>>>>> started this discussion with bad naming of
> > > DEFAULT,
> > > > > but
> > > > > > > this
> > > > > > > > > has
> > > > > > > > > > > > >>>>>>
> > > > > > > > > > > > >>>>> nothing
> > > > > > > > > > > > >>>>
> > > > > > > > > > > > >>>>> to
> > > > > > > > > > > > >>>>>
> > > > > > > > > > > > >>>>>> do with LOG_ONLY (even though it may be
> > > scientific -
> > > > > but
> > > > > > > > SYNC
> > > > > > > > > > > sounds
> > > > > > > > > > > > >>>>>> scientific as well).
> > > > > > > > > > > > >>>>>>
> > > > > > > > > > > > >>>>>> I agree with Ivan, we should not go wild with
> > > > > renaming.
> > > > > > > > > > However, I
> > > > > > > > > > > > >>>>>
> > > > > > > > > > > > >>>> would
> > > > > > > > > > > > >>>
> > > > > > > > > > > > >>>> like to find out what is the meaning behind the
> > > > LOG_ONLY
> > > > > > > name.
> > > > > > > > > Can
> > > > > > > > > > > > >>>>>
> > > > > > > > > > > > >>>> someone
> > > > > > > > > > > > >>>>
> > > > > > > > > > > > >>>>> explain?
> > > > > > > > > > > > >>>>>
> > > > > > > > > > > > >>>>> D.
> > > > > > > > > > > > >>>>>
> > > > > > > > > > > > >>>>>
> > > > > > > > > > > > >>>>
> > > > > > > > > > > > >>>> --
> > > > > > > > > > > > >>>> Best regards,
> > > > > > > > > > > > >>>> Ilya
> > > > > > > > > > > > >>>>
> > > > > > > > > > > > >>>>
> > > > > > > > > > > > >
> > > > > > > > > > > >
> > > > > > > > > > >
> > > > > > > > > >
> > > > > > > > >
> > > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > >
> > > >
> > > >
> > > > --
> > > > Sergey Kozlov
> > > > GridGain Systems
> > > > www.gridgain.com
> > > >
> > >
> >
>

[Dmitriy Pavlov]

Hi Folks,

We have performance suggestions logged during Ignite start. Can we create
data safety suggestions and list all these options during startup?

Arguments about Ignite is distributed and may have backup for protection
make sence.

Who can provide reference to test of such or similar scenario:
- distributed recovery when LOG_ONLY mode is enabled on 2 nodes, 1 backup.
- and 1 node is crashed during WAL logging of transaction with huge number
of records. But node 2 was managed to log all records in TX. (Node1 WAL:
RR crash, Node2 WAL: RRRRRR).
- node 1 returns to cluster
- it should be possible to see consistent state with all TX data after
delta rebalancing.

If such test exist, runs in TC and is not flaky I'm also ok with new
relaxed default.

Sincerely,
Dmitriy Pavlov

пн, 19 февр. 2018 г. в 10:06, Alexey Goncharuk <[hidden email]>:

> In terms of 'safety', Ignite default settings are far beyond optimal. For
> in-memory mode, we have 0 backups by default, which means partition loss in
> a case of node failure, we have readFromBackup=true and PRIMARY_SYNC by
> default which effectively cancels linearizability property for cache
> updates, so setting the default WAL mode to LOG_ONLY does not seem to be a
> bigger evil than it currently is. If we are to move to safer defaults, we
> should change all of the affected sides.
>
> I also want to clarify the difference between guarantees in
> non-fsync modes. We should distinguish the loss of durability (the loss of
> the last update) because the update did not make it to disk and data loss
> because the disk content was shuffled due to an incomplete page write. In
> my understanding, the current situation is:
> FSYNC: loss of durability: not possible, data loss: not possible
> LOG_ONLY: loss of durability: possible only if OS/power fails, data loss:
> possible only if OS/power fails
> BACKGROUND: loss of durability: possible if Ignite process fails, data
> loss: possible only if OS/power fails
>
> The data loss situation can be mitigated in the cluster using a large
> enough replication factor (this is what Dmitriy was describing in the case
> of LOG_ONLY and 3 backups configuration).
>
> Denis,
> I do not think it is fair to compare Ignite defaults to Cassandra's
> defaults because Cassandra is _not_ transactional _eventually consistent_
> datastore, they claim much weaker guarantees than Ignite.
>
> All in all, I'm ok to change the WAL default right now, but I would revisit
> all those settings in 3.0 and made Ignite safe-first.
>
> 2018-02-17 3:24 GMT+03:00 Denis Magda <[hidden email]>:
>
> > Classic relational databases have no choice rather than to use FSYNC by
> > default. RDBMS is all about consistency.
> >
> > Distributed databases try to balance consistency and performance. For
> > instance, why to fsync every update if there is usually 1 backup copy?
> > This is probably why VoltDB [1] and Cassandra use the modes comparable to
> > Ignite's LOG_ONLY.
> >
> > Ignite as a distributed database should care of both consistency and
> > performance.
> >
> > My vote goes to FSYNC, LOG_ONLY (default), BACKGROUND, NONE.
> >
> >
> > [1] https://docs.voltdb.com/UsingVoltDB/CmdLogConfig.php
> >
> > --
> > Denis
> >
> >
> > On Fri, Feb 16, 2018 at 2:14 PM, Dmitriy Setrakyan <
> [hidden email]>
> > wrote:
> >
> > > Vova,
> > >
> > > I hear your concerns, but at the same time I know that one of the
> largest
> > > banks in eastern Europe is using Ignite in LOG_ONLY mode with 3 backups
> > to
> > > move money. The rational is that the probability of failure of 4
> servers
> > at
> > > hardware level at the same time is very low. However, if the JVM
> process
> > > fails on any server, then it can be safely restarted without loosing
> > data.
> > > In my view, this is why LOG_ONLY mode makes sense as a default.
> > >
> > > I still vote to change the default to LOG_ONLY, deprecate the DEFAULT
> > name
> > > altogether and add FSYNC mode instead.
> > >
> > > D.
> > >
> > > On Fri, Feb 16, 2018 at 4:05 PM, Vladimir Ozerov <[hidden email]
> >
> > > wrote:
> > >
> > > > Sergey,
> > > >
> > > > We do not have backups by default either, so essentially we are
> loosing
> > > > data by default. Moreover, backups are less reliable option than
> fsync
> > > > because a lot of users cannot afford putting servers into separate
> > power
> > > > circuits, so a single power failure may easily lead to poweroff of
> the
> > > > whole cluster at once, so data is lost still. This is normal practice
> > > even
> > > > for enterprise deployments (e.g. asynchronous replication).
> > > >
> > > > To make things even worse, we employ PRIMARY_SYNC mode by default! So
> > > even
> > > > if you configured backups, you still may loose data due to a single
> > node
> > > > failure - just shutdown the PRIMARY after commit is confirmed to the
> > > client
> > > > and your recent update will disappers.
> > > >
> > > > So this is what user should do to make himself safe:
> > > > 1) Learn about WAL modes
> > > > 2) Learn about backups
> > > > 3) Learn about synchronization modes
> > > > 4) Cross his fingers that he understood everything correctly and that
> > > there
> > > > are no other hidden surprises in Ignite which could lead to data
> loss.
> > > >
> > > > Way to much for a product, claiming to be A*C*ID and persistent,
> don't
> > > you
> > > > think so?
> > > >
> > > > Leaving deafult WAL mode with fsync resolves all these issues.
> > > >
> > > > Vladimir.
> > > >
> > > >
> > > > On Fri, Feb 16, 2018 at 11:43 PM, Sergey Kozlov <
> [hidden email]>
> > > > wrote:
> > > >
> > > > > I suppose some approaches used by classic databases makes no sense
> > for
> > > > > Ignite. FSYNC requirement for databases has the nature of single
> host
> > > > > solution. If you have corrupted db files you have corrupted (lost)
> > > data.
> > > > >
> > > > > For Ignite the enough number of backups and the failure detecting
> > logic
> > > > can
> > > > > provide the data consistency in term "cluster data consistency".
> > > > >
> > > > >
> > > > >
> > > > > On Fri, Feb 16, 2018 at 8:57 PM, Dmitry Pavlov <
> > [hidden email]>
> > > > > wrote:
> > > > >
> > > > > > Hi, all WAL modes except NONE protects from data consistency
> > problem
> > > > > > (B+Tree, pages, etc), which is why I suggest to avoid saying
> > > > 'corrupted'
> > > > > > about 'unapplied updates'.
> > > > > >
> > > > > > Log Only and Background may cause unapplied updates in case of
> > > > OS/process
> > > > > > failures.
> > > > > >
> > > > > > None mode IMO is not an option in case data consistency is
> needed.
> > > > > >
> > > > > > пт, 16 февр. 2018 г. в 20:49, Valentin Kulichenko <
> > > > > > [hidden email]>:
> > > > > >
> > > > > > > Guys,
> > > > > > >
> > > > > > > While we're on this topic, what is the difference between
> > > BACKGROUND
> > > > > and
> > > > > > > NONE in terms of semantics and provided guarantees? To me it
> > looks
> > > > like
> > > > > > > both guarantee to recover the state since last checkpoint and
> > > > anything
> > > > > > else
> > > > > > > can potentially be lost, so from user perspective they are the
> > > same.
> > > > > Am I
> > > > > > > missing something here?
> > > > > > >
> > > > > > > Also there is the following in Javadoc for NONE: "If an Ignite
> > node
> > > > is
> > > > > > > terminated in NONE mode abruptly, it is likely that the data
> > stored
> > > > on
> > > > > > disk
> > > > > > > is corrupted and work directory will need to be cleared for a
> > node
> > > > > > > restart.". If this is really the case, I'm not sure NONE makes
> > > sense
> > > > at
> > > > > > > all. Why would I enable persistence if I'm likely to clear the
> > > > storage
> > > > > on
> > > > > > > restart?
> > > > > > >
> > > > > > > -Val
> > > > > > >
> > > > > > > On Fri, Feb 16, 2018 at 8:39 AM, Vladimir Ozerov <
> > > > [hidden email]
> > > > > >
> > > > > > > wrote:
> > > > > > >
> > > > > > > > What is the reason to have DEFAULT mode at all if you claim
> > > > LOG_ONLY
> > > > > to
> > > > > > > be
> > > > > > > > completely safe? :)
> > > > > > > >
> > > > > > > > And how it could be safe provided that without fsync we loose
> > > part
> > > > of
> > > > > > WAL
> > > > > > > > itself in case of crash?
> > > > > > > >
> > > > > > > > пт, 16 февр. 2018 г. в 19:32, Dmitry Pavlov <
> > > [hidden email]
> > > > >:
> > > > > > > >
> > > > > > > > > Thank you. Data can't be corrupted in case crash because of
> > WAL
> > > > > > replay
> > > > > > > > > (since completed checkpoint). Physical records are used to
> > > > restore
> > > > > > > > probably
> > > > > > > > > corrupted pages in persistent store (we overwrite so called
> > > 'grey
> > > > > > > zone' -
> > > > > > > > > pages we don't know for sure if they have been written).
> > > > > > > > >
> > > > > > > > > Only one effect is unwritten one or several last
> > transactions.
> > > It
> > > > > is
> > > > > > > not
> > > > > > > > > the same with corrupted data.
> > > > > > > > >
> > > > > > > > > пт, 16 февр. 2018 г. в 19:19, Vladimir Ozerov <
> > > > > [hidden email]
> > > > > > >:
> > > > > > > > >
> > > > > > > > > > Log only mode is not safe - data might be corrupted in
> case
> > > of
> > > > > > system
> > > > > > > > > > crash. Oracle - fsync, Postgres - fsync, SQL Server -
> > fsync,
> > > > > > > Cassandra
> > > > > > > > -
> > > > > > > > > > similar to our “background”.
> > > > > > > > > >
> > > > > > > > > > пт, 16 февр. 2018 г. в 19:11, Dmitry Pavlov <
> > > > > [hidden email]
> > > > > > >:
> > > > > > > > > >
> > > > > > > > > > > Hi Vladimir,
> > > > > > > > > > >
> > > > > > > > > > > What you saying is defenetely make sence.
> > > > > > > > > > >
> > > > > > > > > > > In the same time LOG_ONLY is also safe mode, user will
> be
> > > > able
> > > > > to
> > > > > > > > > restore
> > > > > > > > > > > system after crash. If it is not true, we should create
> > > > > critical
> > > > > > > > ticket
> > > > > > > > > > and
> > > > > > > > > > > fix it.
> > > > > > > > > > >
> > > > > > > > > > > Do you know other databases defaults, such as
> Cassandra,
> > > > > Oracle,
> > > > > > > > > Postgre?
> > > > > > > > > > >
> > > > > > > > > > > Sincerely,
> > > > > > > > > > > Dmitriy Pavlov
> > > > > > > > > > >
> > > > > > > > > > > пт, 16 февр. 2018 г. в 18:41, Vladimir Ozerov <
> > > > > > > [hidden email]
> > > > > > > > >:
> > > > > > > > > > >
> > > > > > > > > > > > Igniters,
> > > > > > > > > > > >
> > > > > > > > > > > > Sorry for pouring oil on the flames, but from
> database
> > > > > > > perspective
> > > > > > > > > > moving
> > > > > > > > > > > > from FSYNC to non-FSYNC mode appears to be a mistake.
> > > When
> > > > > you
> > > > > > > work
> > > > > > > > > > with
> > > > > > > > > > > > database, your main expectation is that it will save
> > your
> > > > > data.
> > > > > > > All
> > > > > > > > > > > > production database vendor make sure that you are
> safe,
> > > not
> > > > > > that
> > > > > > > > you
> > > > > > > > > > are
> > > > > > > > > > > > fast. Moreover, some vendors even prevent you from
> > being
> > > in
> > > > > > > unsafe
> > > > > > > > > mode
> > > > > > > > > > > > (e.g. you cannot disable fsync in SQL Server at all).
> > > > > > > > > > > >
> > > > > > > > > > > > If we continue going in this direction, we will end
> up
> > > > with a
> > > > > > > > > product,
> > > > > > > > > > > > which is unsafe out of the box and require tons of
> > > > > > documentation
> > > > > > > to
> > > > > > > > > > > > understand how to make it safe. Definitely not the
> > right
> > > > > > message
> > > > > > > to
> > > > > > > > > the
> > > > > > > > > > > > market. This is like a car without brakes - would you
> > > like
> > > > to
> > > > > > > drive
> > > > > > > > > it?
> > > > > > > > > > > If
> > > > > > > > > > > > this is Need For Speed game and you have unlimited
> > lives
> > > > > > > (in-memory
> > > > > > > > > > cache
> > > > > > > > > > > > with backing store), then yes. If this is a real life
> > > with
> > > > > > > > > > (persistence)
> > > > > > > > > > > -
> > > > > > > > > > > > then no.
> > > > > > > > > > > >
> > > > > > > > > > > > On Fri, Feb 16, 2018 at 5:20 PM, Dmitriy Setrakyan <
> > > > > > > > > > > [hidden email]>
> > > > > > > > > > > > wrote:
> > > > > > > > > > > >
> > > > > > > > > > > > > Well, I cannot say that I like the name LOG_ONLY,
> > but I
> > > > > would
> > > > > > > > vote
> > > > > > > > > to
> > > > > > > > > > > > keep
> > > > > > > > > > > > > it for now, given that it is already documented in
> > many
> > > > > > places,
> > > > > > > > > > blogs,
> > > > > > > > > > > > and
> > > > > > > > > > > > > examples.
> > > > > > > > > > > > >
> > > > > > > > > > > > > D.
> > > > > > > > > > > > >
> > > > > > > > > > > > > On Fri, Feb 16, 2018 at 8:13 AM, Ivan Rakov <
> > > > > > > > [hidden email]
> > > > > > > > > >
> > > > > > > > > > > > wrote:
> > > > > > > > > > > > >
> > > > > > > > > > > > > > Looks like it's an Ignite term - I've never heard
> > of
> > > it
> > > > > > > outside
> > > > > > > > > > > Ignite
> > > > > > > > > > > > > > scope.
> > > > > > > > > > > > > >
> > > > > > > > > > > > > > Though, renaming existing enum value requires
> > keeping
> > > > old
> > > > > > as
> > > > > > > > > > > > deprecated.
> > > > > > > > > > > > > > DEFAULT is confusing enough to pay this price.
> > > > > > > > > > > > > > As for LOG_ONLY, I think we can keep it as long
> as
> > it
> > > > has
> > > > > > > good
> > > > > > > > > and
> > > > > > > > > > > > > > definitive javadoc.
> > > > > > > > > > > > > >
> > > > > > > > > > > > > > Best Regards,
> > > > > > > > > > > > > > Ivan Rakov
> > > > > > > > > > > > > >
> > > > > > > > > > > > > >
> > > > > > > > > > > > > > On 16.02.2018 17:07, Dmitriy Setrakyan wrote:
> > > > > > > > > > > > > >
> > > > > > > > > > > > > >> Igniters, just to clarify, does the term
> LOG_ONLY
> > > mean
> > > > > > > > anything
> > > > > > > > > in
> > > > > > > > > > > the
> > > > > > > > > > > > > >> industry or is this just an Ignite term?
> > > > > > > > > > > > > >>
> > > > > > > > > > > > > >> D.
> > > > > > > > > > > > > >>
> > > > > > > > > > > > > >> On Fri, Feb 16, 2018 at 8:03 AM, Anton
> Vinogradov
> > <
> > > > > > > > > > > > > >> [hidden email]>
> > > > > > > > > > > > > >> wrote:
> > > > > > > > > > > > > >>
> > > > > > > > > > > > > >> Log only mode: flushes application buffers.
> > > > > > > > > > > > > >>> So, in synced mode without fsync guarantee.
> > That's
> > > > why
> > > > > I
> > > > > > > > > propose
> > > > > > > > > > to
> > > > > > > > > > > > > >>> rename
> > > > > > > > > > > > > >>> it as SYNC.
> > > > > > > > > > > > > >>>
> > > > > > > > > > > > > >>> On Fri, Feb 16, 2018 at 4:49 PM, Ilya Lantukh <
> > > > > > > > > > > [hidden email]
> > > > > > > > > > > > >
> > > > > > > > > > > > > >>> wrote:
> > > > > > > > > > > > > >>>
> > > > > > > > > > > > > >>> I am OK with either FSYNC or STRICT variant.
> > > > > > > > > > > > > >>>>
> > > > > > > > > > > > > >>>> LOG_ONLY name means "log without fsync".
> > > > > > > > > > > > > >>>>
> > > > > > > > > > > > > >>>> On Fri, Feb 16, 2018 at 4:05 PM, Dmitriy
> > > Setrakyan <
> > > > > > > > > > > > > >>>>
> > > > > > > > > > > > > >>> [hidden email]>
> > > > > > > > > > > > > >>>
> > > > > > > > > > > > > >>>> wrote:
> > > > > > > > > > > > > >>>>
> > > > > > > > > > > > > >>>> On Fri, Feb 16, 2018 at 7:02 AM, Ivan Rakov <
> > > > > > > > > > > [hidden email]>
> > > > > > > > > > > > > >>>>>
> > > > > > > > > > > > > >>>> wrote:
> > > > > > > > > > > > > >>>>
> > > > > > > > > > > > > >>>>> Why create a new term to define something
> that
> > > has
> > > > > > > already
> > > > > > > > > been
> > > > > > > > > > > > > >>>>>>
> > > > > > > > > > > > > >>>>> defined?
> > > > > > > > > > > > > >>>>
> > > > > > > > > > > > > >>>>> That makes sense. I'm ok with FSYNC.
> > > > > > > > > > > > > >>>>>> Anton, I don't understand why we should
> rename
> > > > > > LOG_ONLY
> > > > > > > to
> > > > > > > > > > SYNC.
> > > > > > > > > > > > We
> > > > > > > > > > > > > >>>>>> started this discussion with bad naming of
> > > > DEFAULT,
> > > > > > but
> > > > > > > > this
> > > > > > > > > > has
> > > > > > > > > > > > > >>>>>>
> > > > > > > > > > > > > >>>>> nothing
> > > > > > > > > > > > > >>>>
> > > > > > > > > > > > > >>>>> to
> > > > > > > > > > > > > >>>>>
> > > > > > > > > > > > > >>>>>> do with LOG_ONLY (even though it may be
> > > > scientific -
> > > > > > but
> > > > > > > > > SYNC
> > > > > > > > > > > > sounds
> > > > > > > > > > > > > >>>>>> scientific as well).
> > > > > > > > > > > > > >>>>>>
> > > > > > > > > > > > > >>>>>> I agree with Ivan, we should not go wild
> with
> > > > > > renaming.
> > > > > > > > > > > However, I
> > > > > > > > > > > > > >>>>>
> > > > > > > > > > > > > >>>> would
> > > > > > > > > > > > > >>>
> > > > > > > > > > > > > >>>> like to find out what is the meaning behind
> the
> > > > > LOG_ONLY
> > > > > > > > name.
> > > > > > > > > > Can
> > > > > > > > > > > > > >>>>>
> > > > > > > > > > > > > >>>> someone
> > > > > > > > > > > > > >>>>
> > > > > > > > > > > > > >>>>> explain?
> > > > > > > > > > > > > >>>>>
> > > > > > > > > > > > > >>>>> D.
> > > > > > > > > > > > > >>>>>
> > > > > > > > > > > > > >>>>>
> > > > > > > > > > > > > >>>>
> > > > > > > > > > > > > >>>> --
> > > > > > > > > > > > > >>>> Best regards,
> > > > > > > > > > > > > >>>> Ilya
> > > > > > > > > > > > > >>>>
> > > > > > > > > > > > > >>>>
> > > > > > > > > > > > > >
> > > > > > > > > > > > >
> > > > > > > > > > > >
> > > > > > > > > > >
> > > > > > > > > >
> > > > > > > > >
> > > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > > >
> > > > >
> > > > > --
> > > > > Sergey Kozlov
> > > > > GridGain Systems
> > > > > www.gridgain.com
> > > > >
> > > >
> > >
> >
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