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From "Tsuyoshi Ozawa (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (YARN-4301) NM disk health checker should have a timeout
Date Wed, 09 Dec 2015 07:45:11 GMT

    [ https://issues.apache.org/jira/browse/YARN-4301?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15048221#comment-15048221
] 

Tsuyoshi Ozawa commented on YARN-4301:
--------------------------------------

[~suda] thank you for the point. I have some comments about v2 patch - could you update them?

1. About the synchronization of DirectoryCollection,  I got the point you mentioned. The change,
however, causes race condition between states in the class(localDirs, fullDirs, errorDirs,
and numFailures) - e.g. {{DirectoryCollection.concat(errorDirs, fullDirs))}}, {{createNonExistentDirs}}
and other functions cannot work well without synchronization. 

I think the root cause of the problem is to calling {{DC.testDirs}} with synchronization in
{{DC.checkDirs}}. How about releasing lock before calling {{testDirs}} and acquiring lock
after calling {{testDirs}}?

{quote}
synchronized DC.getFailedDirs() can be blocked by synchronized DC.checkDirs(), when File.mkdir()
(called from DC.checkDirs(), via DC.testDirs()) does not return in a moderate timeout.
Hence NodeHealthCheckerServer.isHealthy() gets also blocked.
So I would like to make DC.getXXXs unsynchronized.
{quote}

2. If the thread is preempted by OS and moves to another CPU in multicore environment, gap
can be negative value. Hence I prefer not to abort NodeManager here.
{code:title=NodeHealthCheckerService.java}
+    long diskCheckTime = dirsHandler.getLastDisksCheckTime();
+    long now = System.currentTimeMillis();
+    long gap = now - diskCheckTime;
+    if (gap < 0) {
+      throw new AssertionError("implementation error - now=" + now
+          + ", diskCheckTime=" + diskCheckTime);
+    }
{code}

3. Please move validations of configuration to serviceInit to avoid aborting at runtime.
{code:title=NodeHealthCheckerService.java}
+    long allowedGap = this.diskHealthCheckInterval + this.diskHealthCheckTimeout;
+    if (allowedGap <= 0) {
+      throw new AssertionError("implementation error - interval=" + this.diskHealthCheckInterval
+          + ", timeout=" + this.diskHealthCheckTimeout);
+    }
{code}


> NM disk health checker should have a timeout
> --------------------------------------------
>
>                 Key: YARN-4301
>                 URL: https://issues.apache.org/jira/browse/YARN-4301
>             Project: Hadoop YARN
>          Issue Type: Bug
>            Reporter: Akihiro Suda
>         Attachments: YARN-4301-1.patch, YARN-4301-2.patch, concept-async-diskchecker.txt
>
>
> The disk health checker [verifies a disk|https://github.com/apache/hadoop/blob/96677bef00b03057038157efeb3c2ad4702914da/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-nodemanager/src/main/java/org/apache/hadoop/yarn/server/nodemanager/DirectoryCollection.java#L371-L385]
by executing {{mkdir}} and {{rmdir}} periodically.
> If these operations does not return in a moderate timeout, the disk should be marked
bad, and thus {{nodeInfo.nodeHealthy}} should flip to {{false}}.
> I confirmed that current YARN does not have an implicit timeout (on JDK7, Linux 4.2,
ext4) using [Earthquake|https://github.com/osrg/earthquake], our fault injector for distributed
systems.
> (I'll introduce the reproduction script in a while)
> I consider we can fix this issue by making [{{NodeHealthCheckerServer.isHealthy()}}|https://github.com/apache/hadoop/blob/96677bef00b03057038157efeb3c2ad4702914da/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-nodemanager/src/main/java/org/apache/hadoop/yarn/server/nodemanager/NodeHealthCheckerService.java#L69-L73]
return {{false}} if the value of {{this.getLastHealthReportTime()}} is too old.



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