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From "Haoran Zhang (JIRA)" <j...@apache.org>
Subject [jira] [Comment Edited] (PHOENIX-2405) Improve performance and stability of server side sort for ORDER BY
Date Fri, 24 Jun 2016 21:01:16 GMT

    [ https://issues.apache.org/jira/browse/PHOENIX-2405?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15338747#comment-15338747
] 

Haoran Zhang edited comment on PHOENIX-2405 at 6/24/16 9:00 PM:
----------------------------------------------------------------

Hi [~maryannxue],

I just made a pull request which is tested manually and it seems can work. 

Would you mind having a rough review on it to check whether I'm on the right way this time?

Thank you very much. 


was (Author: rcheungit):
Hi [~maryannxue],

I just made a pull request which is not tested yet, as my test environment was screwed up
when I upgrade it to HBase-1.2 and I'm trying to fix it. 

Would you mind having a rough review on it to check whether I'm on the right way this time?

Thank you very much. 

> 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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