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From "stack (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-17471) Region Seqid will be out of order in WAL if using mvccPreAssign
Date Tue, 24 Jan 2017 23:19:26 GMT

    [ https://issues.apache.org/jira/browse/HBASE-17471?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15836827#comment-15836827

stack commented on HBASE-17471:

[~allan163], what [~carp84] said regards tests passing though there are hanging mvcc transactions;
they are covering up dodgy behavior. This suggestion of yours will help? ' if(we != null &&
mvcc != null && !inMemstore) {...'). You need to get it into next iteration of the

Also agree w/ [~carp84] assessment of the patch and perf numbers. Patch is great. Nice cleanup.

On adding region name to IOE, that will be of no value.... Maybe add the walKey and current
state of the sequence id/mvcc at time of exception... that'd be of some use. Otherwise, I
see you are just porting the code that was there already...

I tried backport to branch-1 but gave up after a few minutes. It is messy.

On the patch:

That is great that the problematic latch is gone (My fault it there in first place).

nit: You want to do more cleanup here?

960	      FSWALEntry entry = new FSWALEntry(txid, key, edits, hri, inMemstore);
961	      entry.stampRegionSequenceId(we);

Stamping sequenceid into Cells could be done in the constructor rather than in stampRegionSequenceId.

Ideal would be a WALKey that took sequenceid in its constructor. That'd be sweet. Can do in
follow-up issue.

I ran my little rig running WALPE on a small HDFS cluster with 1-100 threads. Here's numbers:

||Threads||w/o patch||with patch||

So, about the same.

Let me run ITBLL with chaos on this little cluster for a while with the patch in place. That'll
test some that all is working as expected. I'll be back.

> 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,
>  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

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