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https://issues.apache.org/jira/browse/HBASE-21375?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16666646#comment-16666646
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Duo Zhang commented on HBASE-21375:
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I do not think iterating the queue or not will effect whether a TableQueue can
be executed by multiple workers or not? A worker will iterate the queue but
finally it will poll a procedure and return, then other workers can still poll
from the queue.
> Revisit the lock and queue implementation in MasterProcedureScheduler
> ---------------------------------------------------------------------
>
> Key: HBASE-21375
> URL: https://issues.apache.org/jira/browse/HBASE-21375
> Project: HBase
> Issue Type: Sub-task
> Components: proc-v2
> Reporter: Duo Zhang
> Assignee: Duo Zhang
> Priority: Major
> Fix For: 3.0.0, 2.2.0
>
> Attachments: HBASE-21375-UT.patch, HBASE-21375-UT2.patch,
> HBASE-21375-v1.patch, HBASE-21375-v2.patch, HBASE-21375.patch
>
>
> The problem for the old implementation is that we will only check the first
> procedure in a queue to see if it could run, if it can not, we will remove
> the queue from run queue. So when adding procedure to the scheduler, we have
> to try hard to put the procedure which can be executed in front of the queue,
> if there are corner cases where we fail to do so, it will likely lead to a
> dead lock, that's why we have the tricky code when loading procedures and try
> to add them into the scheduler, and also lots of 'if' in the doAdd method of
> MasterProcedureScheduler. But this is still not enough to make things right,
> so finally [~allan163] and I decided to change the logic in doPoll method,
> where we use a loop to find whether there is a procedure can be executed, not
> only the first one.
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