[jira] [Updated] (TEZ-3967) DAGImpl: dag lock is unfair and can starve the writers

["László Bodor (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/TEZ-3967?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

László Bodor updated TEZ-3967:
------------------------------
    Attachment: TEZ-3967.01.patch

> DAGImpl: dag lock is unfair and can starve the writers
> ------------------------------------------------------
>
>                 Key: TEZ-3967
>                 URL: https://issues.apache.org/jira/browse/TEZ-3967
>             Project: Apache Tez
>          Issue Type: Bug
>            Reporter: Gopal Vijayaraghavan
>            Assignee: László Bodor
>            Priority: Major
>         Attachments: TEZ-3967.01.patch
>
>
> Found when debugging HIVE-20103, that a reader arriving when another reader is active can postpone a writer from obtaining a write-lock.
> This is fundamentally bad for the DAGImpl as useful progress can only happen when the writeLock is held.
> {code}
>   public void handle(DAGEvent event) {
> ...
>     try {
>       writeLock.lock();
> {code}
> {code}
>    java.lang.Thread.State: WAITING (parking)
>         at sun.misc.Unsafe.park(Native Method)
>         - parking to wait for  <0x00007efb02246f40> (a java.util.concurrent.locks.ReentrantReadWriteLock$NonfairSync)
>         at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
>         at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:836)
>         at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireQueued(AbstractQueuedSynchronizer.java:870)
>         at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(AbstractQueuedSynchronizer.java:1199)
>         at java.util.concurrent.locks.ReentrantReadWriteLock$WriteLock.lock(ReentrantReadWriteLock.java:943)
>         at org.apache.tez.dag.app.dag.impl.DAGImpl.handle(DAGImpl.java:1162)
>         at org.apache.tez.dag.app.dag.impl.DAGImpl.handle(DAGImpl.java:149)
>         at org.apache.tez.dag.app.DAGAppMaster$DagEventDispatcher.handle(DAGAppMaster.java:2251)
>         at org.apache.tez.dag.app.DAGAppMaster$DagEventDispatcher.handle(DAGAppMaster.java:2242)
>         at org.apache.tez.common.AsyncDispatcher.dispatch(AsyncDispatcher.java:180)
>         at org.apache.tez.common.AsyncDispatcher$1.run(AsyncDispatcher.java:115)
>         at java.lang.Thread.run(Thread.java:745)
> {code}
> while read-lock is passed around between 
> {code}
>        at org.apache.tez.dag.app.dag.impl.DAGImpl.getDAGStatus(DAGImpl.java:901)
>         at org.apache.tez.dag.app.dag.impl.DAGImpl.getDAGStatus(DAGImpl.java:940)
>         at org.apache.tez.dag.api.client.DAGClientHandler.getDAGStatus(DAGClientHandler.java:73)
> {code}
> calls.



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