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From "Yu Li (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-19358) Improve the stability of splitting log when do fail over
Date Wed, 06 Dec 2017 09:30:00 GMT

    [ https://issues.apache.org/jira/browse/HBASE-19358?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16279909#comment-16279909

Yu Li commented on HBASE-19358:

Thanks for the tests [~tianjingyun], but after a closer look, I found I've asked the wrong
question since {{hbase.regionserver.hlog.splitlog.writer.threads}} is an existing property
rather than newly introduced one.

So basically the idea proposed in this JIRA is like below (please correct me if I stated anything
# Currently we'll start writing data into recovered.edits directory as soon as split starts,
while after patch we will set some "entry flush size" and only start writing entries after
{{WALSplitter#buffers}} reach this size
# Currently we won't close any wap (WriteAndPath) until split done, which will cause plenty
of open pipelines to DN, while after patch we will close the wap at end of each flush round
(or in another word, we possibly will generate more files under recovered.edits for regions
with heavy writes)

If the above descriptions are right, I think the new design won't cause big regression in
recovery time for cluster with light load (few regions on each RS), or at least we could tune
it by setting a correct "entry flush size".

And if the above descriptions are right, I'd suggest to update the design doc to better reflect
the idea. The current one would possibly make people think the core design is to introduce
a thread pool while actually it's not.


> Improve the stability of splitting log when do fail over
> --------------------------------------------------------
>                 Key: HBASE-19358
>                 URL: https://issues.apache.org/jira/browse/HBASE-19358
>             Project: HBase
>          Issue Type: Improvement
>          Components: MTTR
>    Affects Versions: 0.98.24
>            Reporter: Jingyun Tian
>            Assignee: Jingyun Tian
>         Attachments: newLogic.jpg, previousLogic.jpg, split-1-log.png, split-table.png,
> The way we splitting log now is like the following figure:
> !https://issues.apache.org/jira/secure/attachment/12899558/previousLogic.jpg!
> The problem is the OutputSink will write the recovered edits during splitting log, which
means it will create one WriterAndPath for each region. If the cluster is small and the number
of regions per rs is large, it will create too many HDFS streams at the same time. Then it
is prone to failure since each datanode need to handle too many streams.
> Thus I come up with a new way to split log.  
> !https://issues.apache.org/jira/secure/attachment/12899557/newLogic.jpg!
> We cached the recovered edits unless exceeds the memory limits we set or reach the end,
then  we have a thread pool to do the rest things: write them to files and move to the destination.
> The biggest benefit is we can control the number of streams we create during splitting
> it will not exceeds *_hbase.regionserver.wal.max.splitters * hbase.regionserver.hlog.splitlog.writer.threads_*,
but before it is *_hbase.regionserver.wal.max.splitters * the number of region the hlog contains_*.

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