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From "Elliott Clark (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-15146) Don't block on Reader threads queueing to a scheduler queue
Date Wed, 22 Jun 2016 09:05:58 GMT

    [ https://issues.apache.org/jira/browse/HBASE-15146?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15343958#comment-15343958

Elliott Clark commented on HBASE-15146:

bq.That seems based on the fact that there are some clients which don't wait the response
of the previously sent request
Nope, it's all about pushing back before blocking on queueing things that can't be answered
in a reasonable time. You can get the queue full with enough single clients.

The reader is non-blocking. The fact that we were blocking and not acking tcp streams until
after full requests are completed was not a preformance benefit in any way. It was just wrong.
It lost perf in multiple different ways.

To see this in the extreme set the handlers to one, and the call queue length to one. Then
tcpdump and see what happens.

> Don't block on Reader threads queueing to a scheduler queue
> -----------------------------------------------------------
>                 Key: HBASE-15146
>                 URL: https://issues.apache.org/jira/browse/HBASE-15146
>             Project: HBase
>          Issue Type: Bug
>    Affects Versions: 1.2.0
>            Reporter: Elliott Clark
>            Assignee: Elliott Clark
>            Priority: Blocker
>             Fix For: 2.0.0, 1.2.0, 1.3.0
>         Attachments: HBASE-15146-v7.patch, HBASE-15146-v8.patch, HBASE-15146-v8.patch,
HBASE-15146.0.patch, HBASE-15146.1.patch, HBASE-15146.2.patch, HBASE-15146.3.patch, HBASE-15146.4.patch,
HBASE-15146.5.patch, HBASE-15146.6.patch
> Blocking on the epoll thread is awful. The new rpc scheduler can have lots of different
queues. Those queues have different capacity limits. Currently the dispatch method can block
trying to add the the blocking queue in any of the schedulers.
> This causes readers to block, tcp acks are delayed, and everything slows down.

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