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https://issues.apache.org/jira/browse/PHOENIX-2405?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15200618#comment-15200618
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Wang, Gang edited comment on PHOENIX-2405 at 3/17/16 11:35 PM:
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After reading the code of class MappedByteBufferQueue, I think Mnemonic could
be used to replace the temporary mapped file when "totalResultSize >=
thresholdBytes", the writeBuffer and ReadBuffer could be directly obtained from
an instance of Mnemonic BigDataMemAllocator, for this case, we can also use the
memory clustering mechanism provided by Mnemonic to maximize the average
performance over hybrid memory-like resources. Thanks.
was (Author: qichfan):
After reading the code of class MappedByteBufferQueue, I think Mnemonic could
be used to replace the temporary mapped file when "totalResultSize >=
thresholdBytes", the writeBuffer and ReadBuffer could be directly obtained from
instance of Mnemonic BigDataMemAllocator. Thanks.
> Improve 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: Maryann Xue
> 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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