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From "Duo Zhang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-20846) Restore procedure locks when master restarts
Date Thu, 19 Jul 2018 14:51:00 GMT

    [ https://issues.apache.org/jira/browse/HBASE-20846?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16549364#comment-16549364
] 

Duo Zhang commented on HBASE-20846:
-----------------------------------

Review board link:

https://reviews.apache.org/r/67973/

> Restore procedure locks when master restarts
> --------------------------------------------
>
>                 Key: HBASE-20846
>                 URL: https://issues.apache.org/jira/browse/HBASE-20846
>             Project: HBase
>          Issue Type: Sub-task
>    Affects Versions: 2.1.0
>            Reporter: Allan Yang
>            Assignee: Duo Zhang
>            Priority: Major
>             Fix For: 3.0.0, 2.0.2, 2.1.1
>
>         Attachments: HBASE-20846-v1.patch, HBASE-20846-v2.patch, HBASE-20846-v3.patch,
HBASE-20846-v4.patch, HBASE-20846-v4.patch, HBASE-20846-v4.patch, HBASE-20846-v5.patch, HBASE-20846.branch-2.0.002.patch,
HBASE-20846.branch-2.0.patch, HBASE-20846.patch
>
>
> Found this one when investigating ModifyTableProcedure got stuck while there was a MoveRegionProcedure
going on after master restart.
> Though this issue can be solved by HBASE-20752. But I discovered something else.
> Before a MoveRegionProcedure can execute, it will hold the table's shared lock. so,,
when a UnassignProcedure was spwaned, it will not check the table's shared lock since it is
sure that its parent(MoveRegionProcedure) has aquired the table's lock.
> {code:java}
> // If there is parent procedure, it would have already taken xlock, so no need to take
>       // shared lock here. Otherwise, take shared lock.
>       if (!procedure.hasParent()
>           && waitTableQueueSharedLock(procedure, table) == null) {
>           return true;
>       }
> {code}
> But, it is not the case when Master was restarted. The child procedure(UnassignProcedure)
will be executed first after restart. Though it has a parent(MoveRegionProcedure), but apprently
the parent didn't hold the table's lock.
> So, since it began to execute without hold the table's shared lock. A ModifyTableProcedure
can aquire the table's exclusive lock and execute at the same time. Which is not possible
if the master was not restarted.
> This will cause a stuck before HBASE-20752. But since HBASE-20752 has fixed, I wrote
a simple UT to repo this case.
> I think we don't have to check the parent for table's shared lock. It is a shared lock,
right? I think we can acquire it every time we need it.



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