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https://issues.apache.org/jira/browse/PHOENIX-2405?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15363665#comment-15363665
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ASF GitHub Bot commented on PHOENIX-2405:
-----------------------------------------
Github user maryannxue commented on a diff in the pull request:
https://github.com/apache/phoenix/pull/175#discussion_r69668752
--- Diff:
phoenix-core/src/main/java/org/apache/phoenix/execute/SortMergeJoinPlan.java ---
@@ -45,10 +45,7 @@
import org.apache.phoenix.exception.SQLExceptionInfo;
import org.apache.phoenix.execute.TupleProjector.ProjectedValueTuple;
import org.apache.phoenix.expression.Expression;
-import org.apache.phoenix.iterate.DefaultParallelScanGrouper;
-import org.apache.phoenix.iterate.MappedByteBufferQueue;
-import org.apache.phoenix.iterate.ParallelScanGrouper;
-import org.apache.phoenix.iterate.ResultIterator;
+import org.apache.phoenix.iterate.*;
--- End diff --
Please do always check your patch before you submit. This is not the right
coding style, and such changes should never appear in a patch/pull request.
> 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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