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From "Oleg Anastasyev (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-6079) Memtables flush is delayed when having a lot of batchlog activity, making node OOM
Date Mon, 23 Sep 2013 21:23:02 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-6079?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13775679#comment-13775679
] 

Oleg Anastasyev commented on CASSANDRA-6079:
--------------------------------------------

Yeah, this makes stall on get() less probable. 

I could measure how big the impact on common case throughout due to rescan of thombstones,
if you did not performed this measurement earlier.

Yet another idea is to reserve a special thread in CompactionManager for doing compactions
on batchlog (and possibly hints) CF. This way it at least wouldn't delay for a long time.
                
> Memtables flush is delayed when having a lot of batchlog activity, making node OOM
> ----------------------------------------------------------------------------------
>
>                 Key: CASSANDRA-6079
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-6079
>             Project: Cassandra
>          Issue Type: Bug
>            Reporter: Oleg Anastasyev
>            Assignee: Oleg Anastasyev
>            Priority: Minor
>             Fix For: 1.2.11, 2.0.2
>
>         Attachments: NoWaitBatchlogCompaction.diff
>
>
> Both MeteredFlusher and BatchlogManager share the same OptionalTasks thread. So, when
batchlog manager processes its tasks no flushes can occur. Even more, batchlog manager waits
for batchlog CF compaction to finish.
> On a lot of batchlog activity this prevents memtables from flush for a long time, making
the node OOM.
> Fixed this by moving batchlog to its own thread and not waiting for batchlog compaction
to finish.

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