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From "Jonathan Gray (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-1177) Delay when client is located on the same node as the regionserver
Date Fri, 15 May 2009 23:22:45 GMT

    [ https://issues.apache.org/jira/browse/HBASE-1177?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12710021#action_12710021
] 

Jonathan Gray commented on HBASE-1177:
--------------------------------------

I did misunderstand part of your explanation.  The jump in CS is just in this delayed case.

But we should still not close the issue.  It's not the context switching caused by additional
concurrency that hurts us then, it's context switching because there's something else happening.
 The jump in context switches is a symptom of something happening differently along the way
for this special range of payloads.

> Delay when client is located on the same node as the regionserver
> -----------------------------------------------------------------
>
>                 Key: HBASE-1177
>                 URL: https://issues.apache.org/jira/browse/HBASE-1177
>             Project: Hadoop HBase
>          Issue Type: Bug
>    Affects Versions: 0.19.0
>         Environment: Linux 2.6.25 x86_64
>            Reporter: Jonathan Gray
>            Assignee: Jim Kellerman
>            Priority: Blocker
>             Fix For: 0.20.0
>
>         Attachments: ReadDelayTest.java
>
>
> During testing of HBASE-80, we uncovered a strange 40ms delay for random reads.  We ran
a series of tests and found that it only happens when the client is on the same node as the
RS and for a certain range of payloads (not specifically related to number of columns or size
of them, only total payload).  It appears to be precisely 40ms every time.
> Unsure if this is particular to our architecture, but it does happen on all nodes we've
tried.  Issue completely goes away with very large payloads or moving the client.
> Will post a test program tomorrow if anyone can test on a different architecture.
> Making a blocker for 0.20.  Since this happens when you have an MR task running local
to the RS, and this is what we try to do, might also consider making this a blocker for 0.19.1.

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