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https://issues.apache.org/jira/browse/HBASE-5954?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13276059#comment-13276059
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Lars Hofhansl commented on HBASE-5954:
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This is only partially true. It is true for the sync packet stuff that I added,
because this does not require closing the block.
If the block needs to be closed (which causes it to be fsync'ed) it is done
after the ack from the downstream DN and before the ack to the upstream DN.
Here in that case the fsyncs are serial. Looking at the code, that part seems
hard to change.
Good news is: HLog files are smaller than a DFS block, so for HBase we never
run into the 2nd issue.
Semi bad news: HFiles also need to fsync'ed at least on block close, so here
we'd see the issue. But since HFiles are written asynchronously it should be OK.
> Allow proper fsync support for HBase
> ------------------------------------
>
> Key: HBASE-5954
> URL: https://issues.apache.org/jira/browse/HBASE-5954
> Project: HBase
> Issue Type: Improvement
> Reporter: Lars Hofhansl
> Assignee: Lars Hofhansl
> Attachments: 5954-trunk-hdfs-trunk-v2.txt, 5954-trunk-hdfs-trunk.txt,
> hbase-hdfs-744.txt
>
>
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