You are viewing a plain text version of this content. The canonical link for it is here.
Posted to dev@tez.apache.org by "Gopal V (JIRA)" <ji...@apache.org> on 2018/07/06 08:12:00 UTC
[jira] [Created] (TEZ-3967) DAGImpl: dag lock is unfair and can
starve the writers
Gopal V created TEZ-3967:
----------------------------
Summary: 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 V
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.
--
This message was sent by Atlassian JIRA
(v7.6.3#76005)