[jira] [Updated] (THRIFT-1468) Memory leak in TSaslServerTransport

["Mithun Radhakrishnan (Updated) (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/THRIFT-1468?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Mithun Radhakrishnan updated THRIFT-1468:
-----------------------------------------

    Attachment: Main.java

Uploading test-code that illustrates how the WeakHashMap might not be working. (The proposed fix is also in the file.)
                
> 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
>
>
> 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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