[jira] Commented: (HBASE-2957) Release row lock when waiting for wal-sync

["Prakash Khemani (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HBASE-2957?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12905798#action_12905798 ] 

Prakash Khemani commented on HBASE-2957:
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Actually, data consistency is not guaranteed if we return to the HBase client any value which has not yet been sync'd to WAL. But for my use case, and I think for many others, it is OK.






> 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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