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From Semyon Boikov <sboi...@gridgain.com>
Subject Issue with near cache update
Date Tue, 24 Mar 2015 15:11:33 GMT

Today I investigated failures in failover suite and found issue with near
cache update. Now when near cache entry is initialized we store primary
node id, and when value is requested from near cache entry we check that
stored node is still primary (NearCacheEntry.valid()).
Following scenario is possible (reproduces in our test):
- there are two nodes A is primary, B is near
- near cache entry is initialized on B, A is stored in near cache entry as
- new node C joins grid and becomes new primary
- values is updated from C, it is not aware about near reader B and value
in near cache on B is not updated
- node C leaves grid, A again becomes primary
- value is requested from near cache entry on B, it sees that stored node A
is still primary and returns outdated value

As a simple fix I changed GridNearCacheEntry to store current topology
version at the moment when entry was initialized from primary, and method
NearCacheEntry.valid() checks that topology version did not change.
Assuming topology should not change often this fix should not impact near
cache performance.

The only case when topology can change often is usage of client nodes. When
support for client nodes will be fully implemented we will need some way to
check that cache affinity topology did not change.


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