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https://issues.apache.org/jira/browse/HBASE-2957?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12906627#action_12906627
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dhruba borthakur commented on HBASE-2957:
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@Todd: in your proposal you unlock the row before the Hlog is synced. in the
rare case then the Hlog.sync fails, that transaction will be lost but other
readers would have already seen the new value because u released the rowlock.
@Stack. @Jonathan: " simpler adding an ICV batcher/catcher/reservoir/overspill
that sat in front of an actual ICV call?"
I agree and I think that proposal works when the use-case is only ICV. but do
you want the solution generalized so that it works for a workload that does
lots of "puts" into the same record? with the exiting code, all these put calls
will get serialized via the rowlock and syncs to HLog does not get any batching.
> Release row lock when waiting for wal-sync
> ------------------------------------------
>
> Key: HBASE-2957
> URL: https://issues.apache.org/jira/browse/HBASE-2957
> Project: HBase
> Issue Type: Improvement
> Components: regionserver, wal
> Affects Versions: 0.20.0
> Reporter: Prakash Khemani
>
> Is there a reason to hold on to the row-lock while waiting for the WAL-sync
> to be completed by the logSyncer thread?
> I think data consistency will be guaranteed even if the following happens (a)
> the row lock is held while the row is updated in memory (b) the row lock is
> released after queuing the KV record for WAL-syncing (c) the log-sync system
> guarantees that the log records for any given row are synced in order (d) the
> HBase client only receives a success notification after the sync completes
> (no change from the current state)
> I think this should be a huge win. For my use case, and I am sure for others,
> the handler thread spends the bulk of its row-lock critical section time
> waiting for sync to complete.
> Even if the log-sync system cannot guarantee the orderly completion of sync
> records, the "Don't hold row lock while waiting for sync" option should be
> available to HBase clients on a per request basis.
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