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From "Nick Dimiduk (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-9676) AsyncProcess can create more tasks than hbase.client.max.total.tasks
Date Tue, 01 Oct 2013 19:28:24 GMT

    [ https://issues.apache.org/jira/browse/HBASE-9676?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13783246#comment-13783246
] 

Nick Dimiduk commented on HBASE-9676:
-------------------------------------

{noformat}
+  /**
+   * The number of tasks we run in parallel on a single region.
+   * With 1 (the default) , we ensure that the ordering of the queries is respected: we don't
start
+   * a set of operations on a region before the previous one is done. As well, this limits
+   * the pressure we put on the region server.
+   */
   protected final int maxConcurrentTasksPerRegion;
{noformat}

This documentation is very good. Thinking about consistency models and the linear ordering
of writes, I'm concerned about proper documentation of this setting. By setting {{hbase.client.max.perregion.tasks
> 1}} the user has accepted the possibility of the RS ACKing writes out of order. Technically
this is okay, I think, because at this level, the API only makes guarantees about a single
row; so long as edits to a single row are properly grouped, there are no surprises. The user
has also accepted the out-of-order nature of writes across multiple regions; conceptually
this is an extension.

I don't see the second bug fixed in this patch; I'll have to trust you.

+1

> AsyncProcess can create more tasks than hbase.client.max.total.tasks
> --------------------------------------------------------------------
>
>                 Key: HBASE-9676
>                 URL: https://issues.apache.org/jira/browse/HBASE-9676
>             Project: HBase
>          Issue Type: Bug
>          Components: Client
>    Affects Versions: 0.98.0, 0.96.0
>            Reporter: Nicolas Liochon
>            Assignee: Nicolas Liochon
>            Priority: Critical
>             Fix For: 0.98.0, 0.96.1
>
>         Attachments: 9676.v2.patch, 9676.v3.patch, 9676.v4.patch
>
>
> hbase.client.max.total.tasks allows to control the number of tasks in progress. But when
adding tasks, we take only into account the number of tasks currently running, not the one
we're creating.



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