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From Yakov Zhdanov <yzhda...@apache.org>
Subject ATOMIC caches consistency - IEP-12
Date Mon, 25 Dec 2017 15:23:38 GMT
Hello!

I tried to summarize some ideas on how to make ATOMIC caches stay
consistent in case of topology changes.

Imagine partitioned ATOMIC cache with 2 backups configured (primary + 2
backup copies of the partition). One of possible scenarios to get to
primary and backups divergence is the following - update initiating node
sends update operation to primary node, primary node propagates update to 1
of 2 backups and then dies. If initiating node crashes as well (and
therefore cannot retry the operation) then in current implementation system
comes to a situation when 2 copies of the partition present in cluster may
be different. Note that both situations possible - new primary contains the
latest update and backup does not and vice versa. New backup will be
elected according to configured affinity and will rebalance the partition
from random owner, but copies may not be consistent due to described above.

This problem does not affect TRANSACTIONAL caches as 2PC protocol deals
with scenarios of the kind very well.

Here is the link to IEP -
https://cwiki.apache.org/confluence/display/IGNITE/IEP-12+Make+ATOMIC+Caches+Consistent+Again

Sam, Alex G, Vladimir, please share your thoughts.

--Yakov

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