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From "tagus wang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-4423) Improve RCFile::sync(long) 10x
Date Wed, 14 Aug 2013 04:50:51 GMT

    [ https://issues.apache.org/jira/browse/HIVE-4423?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13739221#comment-13739221
] 

tagus wang commented on HIVE-4423:
----------------------------------

this has a bug in this:
System.arraycopy(buffer, buffer.length - prefix - 1, buffer, 0, prefix);
it should be 
System.arraycopy(buffer, buffer.length - prefix, buffer, 0, prefix);

                
> Improve RCFile::sync(long) 10x
> ------------------------------
>
>                 Key: HIVE-4423
>                 URL: https://issues.apache.org/jira/browse/HIVE-4423
>             Project: Hive
>          Issue Type: Improvement
>         Environment: Ubuntu LXC (1 SSD, 1 disk, 32 gigs of RAM)
>            Reporter: Gopal V
>            Assignee: Gopal V
>            Priority: Minor
>              Labels: optimization
>             Fix For: 0.12.0
>
>         Attachments: HIVE-4423.patch
>
>
> RCFile::sync(long) takes approx ~1 second everytime it gets called because of the inner
loops in the function.
> From what was observed with HDFS-4710, single byte reads are an order of magnitude slower
than larger 512 byte buffer reads. 
> Even when disk I/O is buffered to this size, there is overhead due to the synchronized
read() methods in BlockReaderLocal & RemoteBlockReader classes.
> Removing the readByte() calls in RCFile.sync(long) with a readFully(512 byte) call will
speed this function >10x.

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