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https://issues.apache.org/jira/browse/SPARK-11161?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14963522#comment-14963522
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Sean Owen commented on SPARK-11161:
-----------------------------------
Why would it be useful to continue to cache an RDD that can't be used any more?
there is no more reference to it in the controlling driver program in this
case, and it's the only thing that can use it.
There isn't an RDD registry, but if there were, then it would prevent this
situation from occurring, which seems like what you'd expect at least. I expect
RDDs to behave like JVM objects in this regard. I would not expect something to
be hanging on to references to all my objects since I have the references I
need, and indeed, doing so prevents the GC that I want.
You can't unpersist RDDs from the web UI, though that would make sense as a
feature. That's something different.
> Viewing the web UI for the first time unpersists a cached RDD
> -------------------------------------------------------------
>
> Key: SPARK-11161
> URL: https://issues.apache.org/jira/browse/SPARK-11161
> Project: Spark
> Issue Type: Bug
> Components: Spark Core, Web UI
> Affects Versions: 1.5.1
> Reporter: Ryan Williams
> Priority: Minor
>
> This one is a real head-scratcher. [Here's a
> screencast|http://f.cl.ly/items/0P0N413t1V3j2B0A3V1a/Screen%20Recording%202015-10-16%20at%2005.43%20PM.gif]:
> !http://f.cl.ly/items/0P0N413t1V3j2B0A3V1a/Screen%20Recording%202015-10-16%20at%2005.43%20PM.gif!
> The three windows, left-to-right, are:
> * a {{spark-shell}} on YARN with dynamic allocation enabled, at rest with one
> executor. [Here's an example app's
> environment|https://gist.github.com/ryan-williams/6dd3502d5d0de2f030ac].
> * [Spree|https://github.com/hammerlab/spree], opened to the above app's
> "Storage" tab.
> * my YARN resource manager, showing a link to the web UI running on the
> driver.
> At the start, nothing has been run in the shell, and I've not visited the web
> UI.
> I run a simple job in the shell and cache a small RDD that it computes:
> {code}
> sc.parallelize(1 to 100000000, 100).map(_ % 100 -> 1).reduceByKey(_+_,
> 100).setName("foo").cache.count
> {code}
> As the second stage runs, you can see the partitions show up as cached in
> Spree.
> After the job finishes, a few requested executors continue to fill in, which
> you can see in the console at left or the nav bar of Spree in the middle.
> Once that has finished, everything is at rest with the RDD "foo" 100% cached.
> Then, I click the YARN RM's "ApplicationMaster" link which loads the web UI
> on the driver for the first time.
> Immediately, the console prints some activity, including that RDD 2 has been
> removed:
> {code}
> 15/10/16 21:43:12 INFO storage.BlockManagerInfo: Removed broadcast_1_piece0
> on 172.29.46.15:33156 in memory (size: 1517.0 B, free: 7.2 GB)
> 15/10/16 21:43:12 INFO storage.BlockManagerInfo: Removed broadcast_1_piece0
> on demeter-csmaz10-17.demeter.hpc.mssm.edu:56997 in memory (size: 1517.0 B,
> free: 12.2 GB)
> 15/10/16 21:43:13 INFO spark.ContextCleaner: Cleaned accumulator 2
> 15/10/16 21:43:13 INFO storage.BlockManagerInfo: Removed broadcast_0_piece0
> on 172.29.46.15:33156 in memory (size: 1666.0 B, free: 7.2 GB)
> 15/10/16 21:43:13 INFO storage.BlockManagerInfo: Removed broadcast_0_piece0
> on demeter-csmaz10-17.demeter.hpc.mssm.edu:56997 in memory (size: 1666.0 B,
> free: 12.2 GB)
> 15/10/16 21:43:13 INFO spark.ContextCleaner: Cleaned accumulator 1
> 15/10/16 21:43:13 INFO spark.ContextCleaner: Cleaned shuffle 0
> 15/10/16 21:43:13 INFO storage.BlockManager: Removing RDD 2
> 15/10/16 21:43:13 INFO spark.ContextCleaner: Cleaned RDD 2
> {code}
> Accordingly, Spree shows that the RDD has been unpersisted, and I can see in
> the event log (not pictured in the screencast) that an Unpersist event has
> made its way through the various SparkListeners:
> {code}
> {"Event":"SparkListenerUnpersistRDD","RDD ID":2}
> {code}
> Simply loading the web UI causes an RDD unpersist event to fire!
> I can't nail down exactly what's causing this, and I've seen evidence that
> there are other sequences of events that can also cause it:
> * I've repro'd the above steps ~20 times. The RDD always gets unpersisted
> when I've not visited the web UI until the RDD is cached, and when the app is
> dynamically allocating executors.
> * One time, I observed the unpersist to fire without my even visiting the web
> UI at all. Other times I wait a long time before visiting the web UI, so that
> it is clear that the loading of the web UI is causal, and it always is, but
> apparently there's another way for the unpersist to happen, seemingly rarely,
> without visiting the web UI.
> * I tried a couple of times without dynamic allocation and could not
> reproduce it.
> * I've tried a couple of times with dynamic allocation and starting with a
> higher minimum number of executors than 1 and have been unable to reproduce
> it.
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