Amine Bagdouri created SPARK-43523:
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Summary: Memory leak in Spark UI
Key: SPARK-43523
URL: https://issues.apache.org/jira/browse/SPARK-43523
Project: Spark
Issue Type: Bug
Components: Web UI
Affects Versions: 2.4.4
Reporter: Amine Bagdouri
We have a distributed Spark application running on Azure HDInsight using Spark
version 2.4.4.
After a few days of active processing on our application, we have noticed that
the GC CPU time ratio of the driver is close to 100%. We suspected a memory
leak. Thus, we have produced a heap dump and analyzed it using Eclipse Memory
Analyzer.
Here is some interesting data from the driver's heap dump (heap size is 8 GB):
* The estimated retained heap size of String objects (~5M instances) is 3.3
GB. It seems that most of these instances correspond to spark events.
* Spark UI's AppStatusListener instance estimated retained size is 1.1 GB.
* The number of LiveJob objects with status "RUNNING" is 18K, knowing that
there shouldn't be more than 16 live running jobs since we use a fixed thread
pool of 16 threads to run spark queries.
* The number of LiveTask objects is 485K.
* The AsyncEventQueue instance associated to the AppStatusListener has a value
of 854 for dropped events count and a value of 10001 for total events count,
knowing that the dropped events counter is reset every minute and that the
queue's default capacity is 10000.
We think that there is a memory leak in Spark UI. Here is our analysis of the
root cause of this leak:
* AppStatusListener is notified of Spark events using a bounded queue in
AsyncEventQueue.
* AppStatusListener updates its state (kvstore, liveTasks, liveStages,
liveJobs, ...) based on the received events. For example, onTaskStart adds a
task to liveTasks map and onTaskEnd removes the task from liveTasks map.
* When the rate of events is very high, the bounded queue in AsyncEventQueue
is full, some events are dropped and don't make it to AppStatusListener.
* Dropped events that signal the end of a processing unit prevent the state of
AppStatusListener from being cleaned. For example, a dropped onTaskEnd event,
will prevent the task from being removed from liveTasks map, and the task will
remain in the heap until the driver's JVM is stopped.
We were able to confirm our analysis by reducing the capacity of the
AsyncEventQueue (spark.scheduler.listenerbus.eventqueue.capacity=10). After
having launched many spark queries using this config, we observed that the
number of active jobs in Spark UI increased rapidly and remained high even
though all submitted queries have completed. We have also noticed that some
executor task counters in Spark UI were negative, which confirms that
AppStatusListener state does not accurately reflect the reality and that it can
be a victim of event drops.
Suggested fix:
There are some limits today on the number of "dead" objects in
AppStatusListener's maps (for example: spark.ui.retainedJobs). We suggest
enforcing another configurable limit on the number of total objects in
AppStatusListener's maps and kvstore. This should limit the leak in the case of
high events rate, but AppStatusListener stats will remain inaccurate.
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