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https://issues.apache.org/jira/browse/HBASE-17471?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Allan Yang updated HBASE-17471:
-------------------------------
Release Note: MVCCPreAssign is added by HBASE-16698, but pre-assign mvcc is
only used in put/delete path. Other write paths like increment/append still
assign mvcc in ringbuffer's consumer thread. If put and increment are used
parallel. Then seqid in WAL may not increase monotonically. Disorder in wals
will lead to data loss.This patch bring all mvcc/seqid event in wal.append, and
synchronize wal append and mvcc acquirement. No disorder in wal will happen.
Performance test shows no regression with this patch.
> Region Seqid will be out of order in WAL if using mvccPreAssign
> ---------------------------------------------------------------
>
> Key: HBASE-17471
> URL: https://issues.apache.org/jira/browse/HBASE-17471
> Project: HBase
> Issue Type: Bug
> Components: wal
> Affects Versions: 2.0.0, 1.4.0
> Reporter: Allan Yang
> Assignee: Allan Yang
> Priority: Critical
> Attachments: HBASE-17471-duo.patch, HBASE-17471-duo-v1.patch,
> HBASE-17471-duo-v2.patch, HBASE-17471.patch, HBASE-17471.tmp,
> HBASE-17471.v2.patch, HBASE-17471.v3.patch, HBASE-17471.v4.patch,
> HBASE-17471.v5.patch, HBASE-17471.v6.patch
>
>
> mvccPreAssign was brought by HBASE-16698, which truly improved the
> performance of writing, especially in ASYNC_WAL scenario. But mvccPreAssign
> was only used in {{doMiniBatchMutate}}, not in Increment/Append path. If
> Increment/Append and batch put are using against the same region in parallel,
> then seqid of the same region may not monotonically increasing in the WAL.
> Since one write path acquires mvcc/seqid before append, and the other
> acquires in the append/sync consume thread.
> The out of order situation can easily reproduced by a simple UT, which was
> attached in the attachment. I modified the code to assert on the disorder:
> {code}
> if(this.highestSequenceIds.containsKey(encodedRegionName)) {
> assert highestSequenceIds.get(encodedRegionName) < sequenceid;
> }
> {code}
> I'd like to say, If we allow disorder in WALs, then this is not a issue.
> But as far as I know, if {{highestSequenceIds}} is not properly set, some
> WALs may not archive to oldWALs correctly.
> which I haven't figure out yet is that, will disorder in WAL cause data loss
> when recovering from disaster? If so, then it is a big problem need to be
> fixed.
> I have fix this problem in our costom1.1.x branch, my solution is using
> mvccPreAssign everywhere, making it un-configurable. Since mvccPreAssign it
> is indeed a better way than assign seqid in the ringbuffer thread while
> keeping handlers waiting for it.
> If anyone think it is doable, then I will port it to branch-1 and master
> branch and upload it.
>
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