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https://issues.apache.org/jira/browse/CASSANDRA-6945?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13951320#comment-13951320
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Jonathan Ellis commented on CASSANDRA-6945:
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Ship it!
> Calculate liveRatio on per-memtable basis, non per-CF
> -----------------------------------------------------
>
> Key: CASSANDRA-6945
> URL: https://issues.apache.org/jira/browse/CASSANDRA-6945
> Project: Cassandra
> Issue Type: Bug
> Reporter: Aleksey Yeschenko
> Assignee: Aleksey Yeschenko
> Fix For: 2.0.7
>
>
> Currently we recalculate live ratio every doubling of write ops to the CF,
> not to an individual memtable. The value itself is also CF-bound, not
> memtable-bound. This is causing at least several issues:
> 1. Depending on what stage the current memtable is, the live ratio calculated
> can vary *a lot*
> 2. That calculated live ratio will potentially stay that way for quite a
> while - the longer C* process is on, the longer it would stay incorrect
> 3. Incorrect live ratio means inefficient MeteredFlusher - flushing less or
> more often than needed, picking bad candidates for flushing, etc.
> 4. Incorrect live ratio means incorrect size returned to the metrics consumers
> 5. Compaction strategies that rely on memtable size estimation are affected
> 6. All of the above is slightly amplified by the fact that all the memtables
> pending flush would also use that one incorrect value
> Depending on the stage the current memtable at the moment of live ratio
> recalculation is, the value calculated can be *extremely* wrong (say, a
> recently created, fresh memtable - would have a much higher than average live
> ratio).
> The suggested fix is to bind live ratio to individual memtables, not column
> families as a whole, with some optimizations to make recalculations run less
> often by inheriting previous memtable's stats.
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