[jira] [Commented] (PHOENIX-2405) Use Java heap memory instead of memory mapped files during ORDER BY

["James Taylor (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/PHOENIX-2405?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15001811#comment-15001811 ] 

James Taylor commented on PHOENIX-2405:
---------------------------------------

[~maryannxue] - any thoughts?

> Use Java heap memory instead of memory mapped files during ORDER BY
> -------------------------------------------------------------------
>
>                 Key: PHOENIX-2405
>                 URL: https://issues.apache.org/jira/browse/PHOENIX-2405
>             Project: Phoenix
>          Issue Type: Bug
>            Reporter: James Taylor
>
> 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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