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From "Nicolas Liochon (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-11492) The servers do not honor the tcpNoDelay option
Date Fri, 11 Jul 2014 17:50:05 GMT

    [ https://issues.apache.org/jira/browse/HBASE-11492?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14059092#comment-14059092
] 

Nicolas Liochon commented on HBASE-11492:
-----------------------------------------

Nagle and tcp delayed ack makes HBase slow with some usage pattern, with an impact up to 200ms,
so it's definitively needed. I'm not sure that hdfs has the same issue, or at least not for
all patterns. For example hbase could have an issue if the client sends 2 puts in parallel,
but for hdfs there will be a single put so nagle or not nagle won't change much (i think).
But yeah, I found the issue by looking at a scenario with everything in cache.

> The servers do not honor the tcpNoDelay option
> ----------------------------------------------
>
>                 Key: HBASE-11492
>                 URL: https://issues.apache.org/jira/browse/HBASE-11492
>             Project: HBase
>          Issue Type: Bug
>          Components: regionserver
>    Affects Versions: 0.98.0, 0.99.0
>            Reporter: Nicolas Liochon
>            Assignee: Nicolas Liochon
>            Priority: Critical
>             Fix For: 0.99.0, 0.98.5
>
>         Attachments: 11492.v1.patch, 11492.v1.withp1.patch, 11492.v2.patch
>
>
> There is an option to set tcpNoDelay, defaulted to true, but the socket channel is actually
not changed. As a consequence, the server works with nagle enabled. This leads to very degraded
behavior when a single connection is shared between threads. We enter into conflicts with
nagle and tcp delayed ack. 
> Here is an example of performance with the PE tool plus HBASE-11491:
> {noformat}
> oneCon     #client       sleep          exeTime (seconds)                           
 avg latency, sleep excluded (microseconds)
> true           1               0                31                                  
                  310
> false          1               0                31                                  
                  310
> true           2               0                50                                  
                   500
> false          2               0               31                                   
                  310
> true           2                5               488 (including 200s sleeping)       
       2880 
> false          2               5               246  (including 200s sleeping)       
       460
> {noformat}
> The latency is multiple by 5 (2880 vs 460) when the connection is shared. This is the
delayed ack kicking in. This can be fixed by really using tcp no delay.
> Any application sharing the tcp connection between threads has the issue.



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