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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (PHOENIX-2405) Improve performance and stability of server side sort for ORDER BY
Date Sun, 19 Jun 2016 19:37:05 GMT

    [ https://issues.apache.org/jira/browse/PHOENIX-2405?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15338744#comment-15338744
] 

ASF GitHub Bot commented on PHOENIX-2405:
-----------------------------------------

GitHub user RCheungIT opened a pull request:

    https://github.com/apache/phoenix/pull/175

    PHOENIX-2405 Not for merge, just request a review to check whether I'm on the right way

    https://issues.apache.org/jira/browse/PHOENIX-2405

You can merge this pull request into a Git repository by running:

    $ git pull https://github.com/RCheungIT/phoenix PHOENIX-2405-HBase-1.2

Alternatively you can review and apply these changes as the patch at:

    https://github.com/apache/phoenix/pull/175.patch

To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:

    This closes #175
    
----
commit 6566ccd5fa4e8fbfa4fea4e743ca56143d17bc48
Author: RCheungIT <hubert.zhang@outlook.com>
Date:   2016-05-27T17:12:41Z

    PHOENIX-2405 Improve performance and stability of server side sort for
    ORDER BY

----


> Improve performance and stability of server side sort for ORDER BY
> ------------------------------------------------------------------
>
>                 Key: PHOENIX-2405
>                 URL: https://issues.apache.org/jira/browse/PHOENIX-2405
>             Project: Phoenix
>          Issue Type: Bug
>            Reporter: James Taylor
>            Assignee: Haoran Zhang
>              Labels: gsoc2016
>             Fix For: 4.8.0
>
>
> We currently use memory mapped files to buffer data as it's being sorted in an ORDER
BY (see MappedByteBufferQueue). The following types of exceptions have been seen to occur:
> {code}
> Caused by: java.lang.OutOfMemoryError: Map failed
>         at sun.nio.ch.FileChannelImpl.map0(Native Method)
>         at sun.nio.ch.FileChannelImpl.map(FileChannelImpl.java:904)
> {code}
> [~apurtell] has read that memory mapped files are not cleaned up after very well in Java:
> {quote}
> "Map failed" means the JVM ran out of virtual address space. If you search around stack
overflow for suggestions on what to do when your app (in this case Phoenix) encounters this
issue when using mapped buffers, the answers tend toward manually cleaning up the mapped buffers
or explicitly triggering a full GC. See http://stackoverflow.com/questions/8553158/prevent-outofmemory-when-using-java-nio-mappedbytebuffer
for example. There are apparently long standing JVM/JRE problems with reclamation of mapped
buffers. I think we may want to explore in Phoenix a different way to achieve what the current
code is doing.
> {quote}
> Instead of using memory mapped files, we could use heap memory, or perhaps there are
other mechanisms too.



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