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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-3115) HBaseClient wastes 1 TCP packet per RPC
Date Tue, 19 Oct 2010 01:02:29 GMT

    [ https://issues.apache.org/jira/browse/HBASE-3115?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12922391#action_12922391
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Todd Lipcon commented on HBASE-3115:
------------------------------------

FYI I didn't verify with tshark or anything that this actually reduced # of packets, just
kind of assuming. Did either of you guys try it out?

> HBaseClient wastes 1 TCP packet per RPC
> ---------------------------------------
>
>                 Key: HBASE-3115
>                 URL: https://issues.apache.org/jira/browse/HBASE-3115
>             Project: HBase
>          Issue Type: Improvement
>          Components: client
>    Affects Versions: 0.20.1, 0.20.2, 0.20.3, 0.20.4, 0.20.5, 0.20.6, 0.89.20100621
>            Reporter: Benoit Sigoure
>            Assignee: Todd Lipcon
>            Priority: Minor
>         Attachments: hbase-3115.txt
>
>
> In {{ipc/HBaseClient.java}}, the method {{sendParam}} does:
> {code}
> out.writeInt(dataLength);      //first put the data length
> out.write(data, 0, dataLength);//write the data
> {code}
> While analyzing some tcpdump traces tonight, I saw that this consistently translates
to 1 TCP packet with a 4 byte payload followed by another TCP packet with the RPC itself.
 This makes inefficient use of network resources and adversely affects TCP throughput.  I
believe each of those lines translates to a {{write}} system call on the socket's file descriptor
(unnecessary system calls are also bad for performance).  The code attempts to call {{out.flush();}}
but this approach is ineffective on sockets in Java (as far as I empirically noticed over
the past few months).

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