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https://issues.apache.org/jira/browse/CASSANDRA-13736?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16108355#comment-16108355
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Jeff Jirsa commented on CASSANDRA-13736:
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I think blocking for {{TWO}} on batchlog sync is the intended behavior, though
it's not technically in the
[docs|http://cassandra.apache.org/doc/latest/cql/dml.html#batch]
Having a batch only sync'd to one node doesn't seem like much of a guarantee.
> CASSANDRA-9673 cause atomic batch p99 increase 3x
> -------------------------------------------------
>
> Key: CASSANDRA-13736
> URL: https://issues.apache.org/jira/browse/CASSANDRA-13736
> Project: Cassandra
> Issue Type: Bug
> Reporter: xiangzhou xia
> Assignee: xiangzhou xia
>
> When we testing atomic batch in production traffic, we found that p99 latency
> in atomic batch write is 2x-3x worse than 2.2.
> After debuging, we found that the regression is causing by CASSANDRA-9673.
> This patch changed consistency level in batchlog store from ONE to TWO.
> [~iamaleksey] think only block for one batchlog message is a bug in batchlog
> and change it to block for two in CASSANDRA-9673, I think it's actually a
> very good optimization to reduce latency.
> Set the consistency to one will decrease the possibility of slow data node
> (GC, long message queue, etc) affect the latency of atomic batch. In our
> shadow cluster, when we change consistency from two to one, we notice a 2x-3x
> p99 latency drop in atomic batch.
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