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https://issues.apache.org/jira/browse/HADOOP-16278?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16831449#comment-16831449
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Rajat Khandelwal commented on HADOOP-16278:
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There's three sides to this:
# S3Guard is not enableld for us and still it's creating these quantiles.
Looking at the code also, there's no configuration guarding creation of these
quantiles. So maybe we should guard that with a configuration?
# The quantiles once created are left aside without closing them. This causes
{{MutableQuantiles}} to never be Garbage collected since they are scheduled
every second so the Scheduler Service Holds an instance of {{RolloverSample}},
which holds an instance of {{MutableQuantiles}}.
# The scheduler is shared across all {{MutableQuantiles}} and is single
threaded. Scheduling is done via {{scheduleAtFixedRate}}, which builds up a
task queue, instead of {{scheduleAtFixedRate}}, which doesn't.
The patch I've provided solves for 2. You still might want to take care of 1.
Notice that because of the nature of the issue, a solution for 2 is still
required with or without 1. HADOOP-16248 takes care of 3.
> With S3 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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