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https://issues.apache.org/jira/browse/HADOOP-16278?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16835783#comment-16835783
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Aaron Fabbri edited comment on HADOOP-16278 at 5/8/19 5:47 PM:
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Agreed, +1 this simple patch stopping the quantiles on FS close. Also wanted to
say nice work on this Jira [~prongs].
was (Author: fabbri):
Agreed, +1 this simple patch stopping the quantiles on FS close.
> With S3A Filesystem, Long Running services End up Doing lot of GC and
> eventually die
> ------------------------------------------------------------------------------------
>
> Key: HADOOP-16278
> URL: https://issues.apache.org/jira/browse/HADOOP-16278
> Project: Hadoop Common
> Issue Type: Bug
> Components: common, hadoop-aws, metrics
> Affects Versions: 3.1.0, 3.1.1, 3.1.2
> Reporter: Rajat Khandelwal
> Priority: Major
> Fix For: 3.1.3
>
> Attachments: HADOOP-16278.patch, Screenshot 2019-04-30 at 12.52.42
> PM.png, Screenshot 2019-04-30 at 2.33.59 PM.png
>
>
> I'll start with the symptoms and eventually come to the cause.
>
> We are using HDP 3.1 and Noticed that every couple of days the Hive Metastore
> starts doing GC, sometimes with 30 minute long pauses. Although nothing is
> collected and the Heap remains fully used.
>
> Next, we looked at the Heap Dump and found that 99% of the memory is taken up
> by one Executor Service for its task queue.
>
> !Screenshot 2019-04-30 at 12.52.42 PM.png!
> The Instance is Created like this:
> {{ private static final ScheduledExecutorService scheduler = Executors}}
> {{ .newScheduledThreadPool(1, new ThreadFactoryBuilder().setDaemon(true)}}
> {{ .setNameFormat("MutableQuantiles-%d").build());}}
>
> So All the instances of MutableQuantiles are using a Shared single threaded
> ExecutorService
> The second thing to notice is this block of code in the Constructor of
> MutableQuantiles:
> {{this.scheduledTask = scheduler.scheduleAtFixedRate(new
> MutableQuantiles.RolloverSample(this), (long)interval, (long)interval,
> TimeUnit.SECONDS);}}
> So As soon as a MutableQuantiles Instance is created, one task is scheduled
> at Fix Rate. Instead of that, it could schedule them at Fixed Delay (Refer
> HADOOP-16248).
> Now coming to why it's related to S3.
>
> S3AFileSystem Creates an instance of S3AInstrumentation, which creates two
> quantiles (related to S3Guard) with 1s(hardcoded) interval and leaves them
> hanging. By hanging I mean perpetually scheduled. As and when new Instances
> of S3AFileSystem are created, two new quantiles are created, which in turn
> create two scheduled tasks and never cancel them. This way number of
> scheduled tasks keeps on growing without ever getting cleaned up, leading to
> GC/OOM/Crash.
>
> MutableQuantiles has a numInfo field which tells things like the name of the
> metric. From the Heapdump, I found one numInfo and traced all objects
> referencing that.
>
> !Screenshot 2019-04-30 at 2.33.59 PM.png!
>
> There seem to be 300K objects of for the same metric
> (S3Guard_metadatastore_throttle_rate).
> As expected, there are other 300K objects for the other MutableQuantiles
> created by S3AInstrumentation class.
> Although the number of instances of S3AInstrumentation class is only 4.
> Clearly, there is a leak. One S3AInstrumentation instance is creating two
> scheduled tasks to be run every second. These tasks are left scheduled and
> not cancelled when S3AInstrumentation.close() is called. Hence, they are
> never cleaned up. GC is also not able to collect them since they are referred
> by the scheduler.
> Who creates S3AInstrumentation instances? S3AFileSystem.initialize(), which
> is called in FileSystem.get(URI, Configuration). Since hive metastore is a
> service that deals with a lot of Path Objects and hence needs to do a lot of
> calls to FileSystem.get, it's the one to first shows these symptoms.
> We're seeing similar symptoms in AM for long-running jobs (for both Tez AM
> and MR AM).
>
>
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