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https://issues.apache.org/jira/browse/HBASE-6195?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13295241#comment-13295241
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stack commented on HBASE-6195:
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Xing Nice work. When you run MultiThreadsIncrement w/ your patch in place, do
the numbers come out better?
It looks like this increment was originally added by:
{code}
------------------------------------------------------------------------
r1027681 | jgray | 2010-10-26 11:50:13 -0700 (Tue, 26 Oct 2010) | 1 line
HBASE-2946 Increment multiple columns in a row at once
{code}
There is some discussion there that there may be danger around flush time.
Might be useful to review. See
https://issues.apache.org/jira/browse/HBASE-2946?focusedCommentId=12924737&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-12924737
In original patch, it has our updating MemStore before we append to WAL. I
seem to recall that there was a reason why we had this unorthodoxy but I am
unable to find it now.
Thanks for fixing this Xing.
We should backport?
> Increment data will be lost when the memstore is flushed
> --------------------------------------------------------
>
> Key: HBASE-6195
> URL: https://issues.apache.org/jira/browse/HBASE-6195
> Project: HBase
> Issue Type: Bug
> Components: regionserver
> Reporter: Xing Shi
> Assignee: ShiXing
> Fix For: 0.96.0, 0.94.1
>
> Attachments: 6195-trunk-V7.patch, 6195.addendum,
> HBASE-6195-trunk-V2.patch, HBASE-6195-trunk-V3.patch,
> HBASE-6195-trunk-V4.patch, HBASE-6195-trunk-V5.patch,
> HBASE-6195-trunk-V6.patch, HBASE-6195-trunk.patch
>
>
> There are two problems in increment() now:
> First:
> I see that the timestamp(the variable now) in HRegion's Increment() is
> generated before got the rowLock, so when there are multi-thread increment
> the same row, although it generate earlier, it may got the lock later.
> Because increment just store one version, so till now, the result will still
> be right.
> When the region is flushing, these increment will read the kv from snapshot
> and memstore with whose timestamp is larger, and write it back to memstore.
> If the snapshot's timestamp larger than the memstore, the increment will got
> the old data and then do the increment, it's wrong.
> Secondly:
> Also there is a risk in increment. Because it writes the memstore first and
> then HLog, so if it writes HLog failed, the client will also read the
> incremented value.
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