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From "Benjamin Reed (JIRA)" <j...@apache.org>
Subject [jira] Commented: (PIG-599) BufferedPositionedInputStream isn't buffered
Date Wed, 07 Jan 2009 00:05:44 GMT

    [ https://issues.apache.org/jira/browse/PIG-599?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12661384#action_12661384
] 

Benjamin Reed commented on PIG-599:
-----------------------------------

There is a problem with using a buffered stream and compression. we have to do some really
subtle things get the mapping of compression blocks into positions so that the load functions
work out properly. if read ahead happens underneath things break. (it would be excellent if
someone had a better way of doing it.)  in absence of a better idea, i think we should check
that the stream we are buffering and skip the buffering if it as a compressed stream. 

> BufferedPositionedInputStream isn't buffered
> --------------------------------------------
>
>                 Key: PIG-599
>                 URL: https://issues.apache.org/jira/browse/PIG-599
>             Project: Pig
>          Issue Type: Bug
>          Components: impl
>    Affects Versions: types_branch
>            Reporter: Alan Gates
>            Assignee: Alan Gates
>             Fix For: types_branch
>
>         Attachments: loadperf.patch
>
>
> org.apache.pig.impl.io.BufferedPositionedInputStream is not actually buffered.  This
is because it sits atop a FSDataInputStream (somewhere down the stack), which is buffered.
 So to avoid double buffering, which can be bad, BufferedPositionedInputStream was written
without buffering.  But the FSDataInputStream is far enough down the stack that it is still
quite costly to call read() individually for each byte.  A run through a profiler shows that
a fair amount of time is being spent in BufferedPositionedInputStream.read().

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