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https://issues.apache.org/jira/browse/HBASE-2957?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12906558#action_12906558
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stack commented on HBASE-2957:
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@Dhruba How does memstore.inflight get flipped to be memstore.committed?
Safely? There are some existing mechanisms that might be of help. There is a
read/write consistency class in hbase
http://hbase.apache.org/docs/r0.89.20100726/xref/org/apache/hadoop/hbase/regionserver/ReadWriteConsistencyControl.html#1
that is used around memstore updates to help keep the reads and scans 'clean';
i.e. prevents reading of partial updates on a row (There are some known
caveats). And then in KeyValue, there is a 'special' extra timestamp used
ensuring memstore consistency:
http://hbase.apache.org/docs/r0.89.20100726/xref/org/apache/hadoop/hbase/KeyValue.html#216
Would it be simpler adding an ICV batcher/catcher/reservoir/overspill that sat
in front of an actual ICV call? It would accumulate ICVs while WAL was busy
syncing. The ICV resevoir would be an optional facility; you'd ask for it by
setting a flag on the ICV call. On return, the actual ICV would check the
reservoir to see if any ICVs had been accumulating while it was off syncing.
If any, it'd suck them all up and apply the ICVs in a batch. We'd need to add
a new batch ICV call, one that added a block of ICVs to the WAL and that then
did the memstore updates playing the content of the batch one at a time. We'd
return to the client as soon as we'd added an ICV to the revervoir not waiting
on WAL
> 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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