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From "Jeffrey Zhong (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-8729) distributedLogReplay may hang during chained region server failure
Date Tue, 11 Jun 2013 22:00:20 GMT

    [ https://issues.apache.org/jira/browse/HBASE-8729?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13680741#comment-13680741

Jeffrey Zhong commented on HBASE-8729:

[~saint.ack@gmail.com] Thanks for the good comments!
I'll address your first two comments in the next patch(Ted addressed the second one already
in the v2 patch). The interesting point is your last comment:
Rather than a log replay handler, should we instead have M_SERVER_SHUTDOWN be its own type...
and then make N executor slots for server shutdown handling rather than for log reaplay? Would
then make the exit of server shutdown handler nicer in that when we leave it, we have processed
the server rather than as we have in this patch where we go off to another executor for completion?
If we don't introduce the new log replay handler, setting N is tricky and its value has to
be big enough so that we won't end up in issue of the JIRA. 
The other alternative(not clean and error prone) is using one pool while limiting logReplay
can use up to MaxThreads - 3 slots in order not to block all threads in the pool. How do you
think? Thanks.

> distributedLogReplay may hang during chained region server failure
> ------------------------------------------------------------------
>                 Key: HBASE-8729
>                 URL: https://issues.apache.org/jira/browse/HBASE-8729
>             Project: HBase
>          Issue Type: Bug
>          Components: MTTR
>            Reporter: Jeffrey Zhong
>            Assignee: Jeffrey Zhong
>             Fix For: 0.98.0, 0.95.2
>         Attachments: 8729-v2.patch, hbase-8729.patch
> In a test, half cluster(in terms of region servers) was down and some log replay had
incurred chained RS failures(receiving RS of a log replay failed again). 
> Since by default, we only allow 3 concurrent SSH handlers(controlled by {code}this.executorService.startExecutorService(ExecutorType.MASTER_SERVER_OPERATIONS,conf.getInt("hbase.master.executor.serverops.threads",
> If all 3 SSH handlers are doing logReplay(blocking call) and one of receiving RS fails
again then logReplay will hang because regions of the newly failed RS can't be re-assigned
to another live RS(no ssh handler will be processed due to max threads setting) and existing
log replay will keep routing replay traffic to the dead RS.
> The fix is to submit logReplay work into a separate type of executor queue in order not
to block SSH region assignment so that logReplay can route traffic to a live RS after retries
and move forward. 

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