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From "Kihwal Lee (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-2080) Speed up DFS read path
Date Fri, 17 Jun 2011 14:56:48 GMT

    [ https://issues.apache.org/jira/browse/HDFS-2080?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13051115#comment-13051115

Kihwal Lee commented on HDFS-2080:

The checksum was worked on previously in HADOOP-6148 and HADOOP-6166. Due to implicit data
copying when crossing JNI boundary, it was reimplemented in JAVA.  This work will solve the
problem and get us back to faster native code. I imagine there are other places we could apply
the NIO direct buffer + JNI + native code combination.  

In my experiment, zlib was already capable of doing more than most clients can ingest. On
a system with 2GHz E5335 (Clovertown) processors running CentOS5, the CRC32 in zlib could
do 2.5 GB/s if everything comes from cache (on a 64KB buffer). So in my opinion, although
they look seriously cool, the item number 4 and 5 can wait.

> Speed up DFS read path
> ----------------------
>                 Key: HDFS-2080
>                 URL: https://issues.apache.org/jira/browse/HDFS-2080
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: hdfs client
>    Affects Versions: 0.23.0
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>             Fix For: 0.23.0
> I've developed a series of patches that speeds up the HDFS read path by a factor of about
2.5x (~300M/sec to ~800M/sec for localhost reading from buffer cache) and also will make it
easier to allow for advanced users (eg hbase) to skip a buffer copy. 

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