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https://issues.apache.org/jira/browse/HBASE-17085?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15669360#comment-15669360
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ramkrishna.s.vasudevan commented on HBASE-17085:
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My thing was based on the fact that since we call sync(txid), it is sure that
when a sync call comes with txid 2 then surely we will have a append with txid
2. So that is when the sync will be called. I tested that with PE tool and
things worked fine for me. So do you think of the case where sync() is called
without txid? May be I did not test that case as PE actual case is with
sync(txid). It can atleast reduce in the number of sync calls.
> 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-v2.patch,
> HBASE-17085-v2.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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