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https://issues.apache.org/jira/browse/HBASE-17085?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15663866#comment-15663866
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ramkrishna.s.vasudevan commented on HBASE-17085:
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Our comments crossed. Yes what you see is right. But if you see the number of
syncFutures it is quite high. My point was that why is that we have so many
syncFutures whereas the append txid trailing so much behind.
> AsyncFSWAL may issue unnecessary AsyncDFSOutput.sync
> ----------------------------------------------------
>
> Key: HBASE-17085
> URL: https://issues.apache.org/jira/browse/HBASE-17085
> Project: HBase
> Issue Type: Sub-task
> Components: wal
> Affects Versions: 2.0.0
> Reporter: Duo Zhang
> Assignee: Duo Zhang
> Fix For: 2.0.0
>
> Attachments: HBASE-17085-v1.patch, HBASE-17085.patch
>
>
> The problem is in appendAndSync method, we will issue an AsyncDFSOutput.sync
> if syncFutures is not empty. The SyncFutures in syncFutures can only be
> removed after an AsyncDFSOutput.sync comes back, so before the
> AsyncDFSOutput.sync actually returns, we will always issue an
> AsyncDFSOutput.sync after an append even if there is no new sync request.
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