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https://issues.apache.org/jira/browse/HBASE-2467?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12859103#action_12859103
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Todd Lipcon commented on HBASE-2467:
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JD, the issue here is that group commit ends up creating "bubbles". With the
HDFS-895 code, calling sync doesn't block other syncers or writers, so each
thread can just sync its own edits.
There's a slight improvement to be made by doing batching on a very small
scale, to increase HDFS packet size if the edits are <512 bytes, but this patch
resulted in a 3-5x speed increase without having to turn on deferred log flush.
> Concurrent flushers in HLog sync using HDFS-895
> -----------------------------------------------
>
> Key: HBASE-2467
> URL: https://issues.apache.org/jira/browse/HBASE-2467
> Project: Hadoop HBase
> Issue Type: Improvement
> Components: regionserver
> Reporter: Todd Lipcon
> Assignee: Todd Lipcon
> Attachments: hbase-2467.txt
>
>
> HDFS-895 changes hflush() to be able to run concurrently from multiple
> threads, where flushes can be concurrent with further writes to the same file.
> We need to rip out/amend the group commit code a bit to take advantage of
> this.
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