[jira] [Commented] (PHOENIX-2405) Improve performance and stability of server side sort for ORDER BY

["ASF GitHub Bot (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/PHOENIX-2405?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15363643#comment-15363643 ] 

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_r69667743
  
    --- Diff: phoenix-core/src/main/java/org/apache/phoenix/iterate/SpoolingByteBufferSegmentQueue.java ---
    @@ -0,0 +1,357 @@
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    +package org.apache.phoenix.iterate;
    +
    +import org.apache.commons.io.input.CountingInputStream;
    +import org.apache.commons.io.output.DeferredFileOutputStream;
    +
    +import org.apache.phoenix.memory.MemoryManager;
    +import org.apache.phoenix.memory.MemoryManager.MemoryChunk;
    +import org.apache.phoenix.query.QueryServices;
    +import org.apache.phoenix.query.QueryServicesOptions;
    +
    +
    +import java.io.*;
    +import java.util.AbstractQueue;
    +import java.util.Iterator;
    +
    +import java.util.concurrent.atomic.AtomicInteger;
    +
    +import static org.apache.phoenix.monitoring.GlobalClientMetrics.*;
    +
    +
    +public abstract class SpoolingByteBufferSegmentQueue<T>  extends AbstractQueue<T> {
    --- End diff --
    
    The logic is very confusing here. My idea was to extend or modify the current SpoolingResultIterator so that it can take a ResultEntry and/or a Tuple as a record. But meanwhile this does not have to do with the XXXQueue here. XXXQueue deals with the priority queue logic and SpoolingXXX deals with the deferred byte buffer logic. Let me know whether you understand how it's supposed to work.


> 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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