[jira] [Commented] (ZOOKEEPER-1505) Multi-thread CommitProcessor

["Hadoop QA (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/ZOOKEEPER-1505?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13475336#comment-13475336 ] 

Hadoop QA commented on ZOOKEEPER-1505:
--------------------------------------

-1 overall.  Here are the results of testing the latest attachment 
  http://issues.apache.org/jira/secure/attachment/12548952/ZOOKEEPER-1505.patch
  against trunk revision 1391526.

    +1 @author.  The patch does not contain any @author tags.

    +1 tests included.  The patch appears to include 3 new or modified tests.

    +1 javadoc.  The javadoc tool did not generate any warning messages.

    +1 javac.  The applied patch does not increase the total number of javac compiler warnings.

    -1 findbugs.  The patch appears to introduce 1 new Findbugs (version 1.3.9) warnings.

    +1 release audit.  The applied patch does not increase the total number of release audit warnings.

    +1 core tests.  The patch passed core unit tests.

    +1 contrib tests.  The patch passed contrib unit tests.

Test results: https://builds.apache.org/job/PreCommit-ZOOKEEPER-Build/1219//testReport/
Findbugs warnings: https://builds.apache.org/job/PreCommit-ZOOKEEPER-Build/1219//artifact/trunk/build/test/findbugs/newPatchFindbugsWarnings.html
Console output: https://builds.apache.org/job/PreCommit-ZOOKEEPER-Build/1219//console

This message is automatically generated.
                
> Multi-thread CommitProcessor
> ----------------------------
>
>                 Key: ZOOKEEPER-1505
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-1505
>             Project: ZooKeeper
>          Issue Type: Improvement
>          Components: server
>    Affects Versions: 3.4.3, 3.4.4, 3.5.0
>            Reporter: Jay Shrauner
>            Assignee: Jay Shrauner
>              Labels: performance, scaling
>             Fix For: 3.5.0
>
>         Attachments: ZOOKEEPER-1505.patch, ZOOKEEPER-1505.patch, ZOOKEEPER-1505.patch
>
>
> CommitProcessor has a single thread that both pulls requests off its queues and runs all downstream processors. This is noticeably inefficient for read-intensive workloads, which could be run concurrently. The trick is handling write transactions. I propose multi-threading this code according to the following two constraints
>   - each session must see its requests responded to in order
>   - all committed transactions must be handled in zxid order, across all sessions
> I believe these cover the only constraints we need to honor. In particular, I believe we can relax the following:
>   - it does not matter if the read request in one session happens before or after the write request in another session
> With these constraints, I propose the following threads
>   - 1    primary queue servicing/work dispatching thread
>   - 0-N  assignable worker threads, where a given session is always assigned to the same worker thread
> By assigning sessions always to the same worker thread (using a simple sessionId mod number of worker threads), we guarantee the first constraint-- requests we push onto the thread queue are processed in order. The way we guarantee the second constraint is we only allow a single commit transaction to be in flight at a time--the queue servicing thread blocks while a commit transaction is in flight, and when the transaction completes it clears the flag.
> On a 32 core machine running Linux 2.6.38, achieved best performance with 32 worker threads for a 56% +/- 5% improvement in throughput (this improvement was measured on top of that for ZOOKEEPER-1504, not in isolation).
> New classes introduced in this patch are:
>     WorkerService (also in ZOOKEEPER-1504): ExecutorService wrapper that makes worker threads daemon threads and names then in an easily debuggable manner. Supports assignable threads (as used here) and non-assignable threads (as used by NIOServerCnxnFactory).

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