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https://issues.apache.org/jira/browse/THRIFT-1468?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13174972#comment-13174972
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Aaron T. Myers commented on THRIFT-1468:
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bq. I can confirm that the newest patch works. (This patch also has the
comments you'd requested for.) Ran overnight, and the latest heap-dumps don't
indicate a build-up of WeakHashMap$Entry objects.
That's great! Thanks a lot for testing that out, Mithun. The patch and the
comment you added look good to me.
> Memory leak in TSaslServerTransport
> -----------------------------------
>
> Key: THRIFT-1468
> URL: https://issues.apache.org/jira/browse/THRIFT-1468
> Project: Thrift
> Issue Type: Bug
> Components: Java - Library
> Affects Versions: 0.5, 0.9
> Reporter: Mithun Radhakrishnan
> Labels: OOM, WeakHashMap, WeakReference
> Attachments: Main.java,
> THRIFT-1468-Memory_leak_in_TSaslServerTransport.patch, thrift-1468.patch
>
>
> I'm working on the HCatalog project. HCatalog uses a (slightly dated) version
> of Hive that in turn depends on libthrift-0.5.0. The HCatalog-server is a
> continuously running process that serves (meta)data over thrift. (The bug I
> describe is related to HCATALOG-183.)
> We observed that on running the HCatalog-server with continuous
> client-requests, the memory footprint of the server grows steadily, until we
> see an OutOfMemoryError exception. I took a memory snapshot of the running
> process, to check for leaks. I noticed that the majority of the memory (over
> 1.3GB) was being consumed by the
> org.apache.thrift.transport.TSaslServerTransport$Factory::transportMap. There
> were over 52000 instances of WeakHashMap$Entry, consuming 3MB of
> shallow-heap, and 1.3GB of retained heap.
> I suspect that entries in the WeakHashMap (transportMap) are not being
> collected during GC, as is expected in code. That would only be so if there
> are outstanding hard-references to the key in the map (TTransport).
> From the code in TSaslTransport and TSaslServerTransport, it appears that
> there is an inadvertent cyclic reference that the runtime is unable to detect:
> 1. TSaslTransport has a (hard) back-reference to the "underlyingTransport",
> i.e. TTransport.
> 2. TSaslServerTransport::Factory::transportMap is a WeakHashMap< TTransport,
> TSaslServerTransport >. Here, the "underlyingTransport" is mapped back to the
> decorating TSaslServerTransport.
> From #2, an entry can only be GCed if there's no outstanding hard-reference
> to the TTransport. But from #1, the hard-reference comes from the value-part
> of the hashmap entry. The runtime can't deduce that there's a cycle,
> presumably because it's not explicit.
> (I'll be attaching a sample program to better illustrate the WeakHashMap
> behaviour, in case I've botched the explanation above.)
> The simple solution would be to change the back-reference in #1 into a
> WeakReference. I'll attach a patch here that might be suitable.
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