[
https://issues.apache.org/jira/browse/PHOENIX-2405?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15003357#comment-15003357
]
Andrew Purtell edited comment on PHOENIX-2405 at 11/13/15 1:29 AM:
-------------------------------------------------------------------
bq. This would basically mean that we'd be writing files when the sort spills
to disk instead of using memory mapped files.
I think you're at the mercy of the JVM and OS when using mapped files, and this
has already proven to be a fatal route for some users. Manually spilling
instead if in-effect letting the OS do that by paging in and out the mmapped
file is a fine solution.
was (Author: apurtell):
bq. This would basically mean that we'd be writing files when the sort spills
to disk instead of using memory mapped files.
I think you're at the mercy of the JVM and OS when using mapped files, and this
has already proven to be a fatal route for some users. "Manually" spilling
instead if in-effect letting the OS do that by paging in and out the mmapped
file is a fine solution.
> 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.
--
This message was sent by Atlassian JIRA
(v6.3.4#6332)
