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From "Jeff Jirsa (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-13736) CASSANDRA-9673 cause atomic batch p99 increase 3x
Date Tue, 01 Aug 2017 04:20:00 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-13736?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16108355#comment-16108355
] 

Jeff Jirsa commented on CASSANDRA-13736:
----------------------------------------

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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