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https://issues.apache.org/jira/browse/HIVE-3098?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13411778#comment-13411778
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Rohini Palaniswamy commented on HIVE-3098:
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@Ashutosh
bq. to workaround underlying Filesystem issue, lets just disable the fs.cache
via config parameter. Disabling cache will plug the memory leak by not filling
FS cache.
Disabling fs.cache is not going to matter. We are already getting a new
FileSystem object for every request and the fs.cache is not used at all. The
newly created FileSystem objects are still going to be in memory until garbage
collected. And they don't get garbage collected for some reason (We have not
analyzed what else is holding reference to them) as the experiments Mithun ran
with fs.cache disabled did not make any difference.
bq. Once FSContext apis are declared stable for other projects to consume, we
can switch over to those where the promise is that underlying problem is fixed.
As Daryn had mentioned in previous comments, this is not going to solve the
problem at all.
We need to fix this. It is not good to have to restart the metastore server
every week or two. I see two possible interim fixes until it is solved in core
hadoop itself for all applications.
1) Disable fs.cache and do fs.close() after every filesystem call in the code.
If there is a place to put the fs.close() after every request is executed it
is easy. Or you might have to put fs.close() in too many places. Anyways it is
not going to be good for performance.
2) Add the fs.close() logic after a timeout to the current patch. Mithun was
already working on this. I can't understand why you think it adds too much
complexity. Other applications are already doing this. It will be difficult to
answer to the Ops guys why we have a software that needs to be restarted often.
> Memory leak from large number of FileSystem instances in FileSystem.CACHE.
> (Must cache UGIs.)
> ---------------------------------------------------------------------------------------------
>
> Key: HIVE-3098
> URL: https://issues.apache.org/jira/browse/HIVE-3098
> Project: Hive
> Issue Type: Bug
> Components: Shims
> Affects Versions: 0.9.0
> Environment: Running with Hadoop 20.205.0.3+ / 1.0.x with security
> turned on.
> Reporter: Mithun Radhakrishnan
> Assignee: Mithun Radhakrishnan
> Attachments: HIVE-3098.patch
>
>
> The problem manifested from stress-testing HCatalog 0.4.1 (as part of testing
> the Oracle backend).
> The HCatalog server ran out of memory (-Xmx2048m) when pounded by 60-threads,
> in under 24 hours. The heap-dump indicates that hadoop::FileSystem.CACHE had
> 1000000 instances of FileSystem, whose combined retained-mem consumed the
> entire heap.
> It boiled down to hadoop::UserGroupInformation::equals() being implemented
> such that the "Subject" member is compared for equality ("=="), and not
> equivalence (".equals()"). This causes equivalent UGI instances to compare as
> unequal, and causes a new FileSystem instance to be created and cached.
> The UGI.equals() is so implemented, incidentally, as a fix for yet another
> problem (HADOOP-6670); so it is unlikely that that implementation can be
> modified.
> The solution for this is to check for UGI equivalence in HCatalog (i.e. in
> the Hive metastore), using an cache for UGI instances in the shims.
> I have a patch to fix this. I'll upload it shortly. I just ran an overnight
> test to confirm that the memory-leak has been arrested.
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