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From "graham sanderson (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-6944) liveRatio jumps to max when Memtable is empty
Date Wed, 06 Aug 2014 08:23:14 GMT


graham sanderson commented on CASSANDRA-6944:

Perhaps all these comments belong in CASSANDRA-6945 after all, but just finishing train of
thought... things now seem a bit strange when threads are racing.

liveRatio and liveRatioComputedAt T can be passed from memtable X to a subsequent memtable
Y before liveRatio for X at T is computed. liveRatio may then (I think) be computed for X
or Y or Z (depending on where threads are at when MeteringRunnable instances for T executes)
-  not sure which is preferable, but if it is X, then the liveRatio will not be applied to
its successors (who may then not update their live ratio for some time)

> liveRatio jumps to max when Memtable is empty
> ---------------------------------------------
>                 Key: CASSANDRA-6944
>                 URL:
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Core
>         Environment: SUSE Linux Enterprise 11 (64-bit)
>            Reporter: Erik Hansen
>            Assignee: Aleksey Yeschenko
>            Priority: Minor
>              Labels: memtables
> liveRatio calculation on an empty memtable results in a value of Infinity since memtable.currentSize=0.
 Infinity then gets capped at the liveRatio max of 64.
> {noformat}
> WARN [MemoryMeter:1] 2014-03-19 09:26:59,483 (line 441) setting live ratio
to maximum of 64.0 instead of Infinity
> INFO [MemoryMeter:1] 2014-03-19 09:26:59,485 (line 452) CFS(Keyspace='system',
ColumnFamily='compactions_in_progress') liveRatio is 64.0 (just-counted was 64.0).  calculation
took 7ms for 0 cells
> {noformat}
> Jumping liveRatio to the max value based on an empty Memtable leads to more frequent
flushing than may be necessary.
> CASSANDRA-4243 previously addressed this issue, but was resolved as fixed by CASSANDRA-3741.
 It does not appear this issue has been fixed as of 2.0.5

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