The reason behind locking backup copy

[voipp]

Hi, Igntrs! Consider primary node P, backup node B for some key1. When we
create lock on this key (at primary node) :

IgniteCache<Object, Object> primaryCache =
primaryIgnite.cache(DEFAULT_CACHE_NAME);

primaryCache.lock("key1").lock()

After lock acquired on primary node, the GridCacheMvccCandidate would be
created on backup node .

What is the point of creating candidate on backup node ? I cannot find any
reason for this.
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*Best Regards,*

*Kuznetsov Aleksey*