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https://issues.apache.org/jira/browse/HBASE-17471?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15837210#comment-15837210
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Allan Yang commented on HBASE-17471:
------------------------------------
Sorry, replay would expect some delays 'Cause Chinese spring festival vacation
is coming. But still, I'm still working on this issue.
1.
{quote}
what Yu Li said regards tests passing though there are hanging mvcc
transactions; they are covering up dodgy behavior. This suggestion of yours
will help?
{quote}
Yes, It would help like I said in this
[comment|https://issues.apache.org/jira/browse/HBASE-17471?focusedCommentId=15835553&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-15835553].
But, there is a different opinion. [~Apache9] said {quote}If the problem only
happens in UTs then let's just modify the UTs...{quote} . So I'm not sure
whether to add these code but making code 'mess', or open another issue to
modify those problematic UTs and HBASE-17506 also. [~stack], please give me
your advice.
2.
As for [~tedyu]'s advice, I will include them in the next patch, and upload it
soon
3.
{quote}
Stamping sequenceid into Cells could be done in the constructor rather than in
stampRegionSequenceId.
nit: You want to do more cleanup here?
{quote}
Yes, I want to do it in a new issue, but not this one. Since I have a sense
that, we actually don't need to stamp mvcc/seqid to cells in the wal endits. We
only need to stamp them to cells in the memstore. I want to open an new issue
to discuss later. So, let's keep it in this patch
4.
{quote}
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.
{quote}
Yes, please verify this patch with ITBLL , and thank you very much, [~stack]!
5.
{quote}
And it seems still some efforts to take for branch-1 patch. IMO it's necessary
to check the perf data for branch-1 since the write path there is different
from 2.0 (append wal -> write memstore -> sync wal v.s. append wal -> sync wal
-> write memstore). Thanks.
{quote}
As we tested this patch in our custom HBase-1.1.2, there is no regression
either. The order of steps in {{doMiniBatchMutation}} will not influence the
mvcc assign. But still, if I have time, I will post data on branch-1. [~carp84]
6.
{quote}
Are you going to attach patch for branch-1 ?
{quote}
Sure, but there may be some delay, sorry for that.
> 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
>
>
> 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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