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From "Knut Anders Hatlen (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (DERBY-5730) DataDictionaryImpl leaks references to itself via SYSFUN_AD
Date Fri, 27 Apr 2012 09:03:57 GMT

     [ https://issues.apache.org/jira/browse/DERBY-5730?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Knut Anders Hatlen updated DERBY-5730:
--------------------------------------

    Attachment: Sysfun.java

Attaching a repro that exposes the leak.

The repro repeatedly boot a database, performs some db operations, and shuts down the database.
One of the db operations it performs, is preparing a statement that calls one of the SYSFUN
functions, and it is a different function in each iteration.

When running the repro with -Xmx20M, I see an OutOfMemoryError. If I comment out the preparing
of the function call, the repro completes successfully with -Xmx5M.
                
> DataDictionaryImpl leaks references to itself via SYSFUN_AD
> -----------------------------------------------------------
>
>                 Key: DERBY-5730
>                 URL: https://issues.apache.org/jira/browse/DERBY-5730
>             Project: Derby
>          Issue Type: Bug
>          Components: Services
>    Affects Versions: 10.9.0.0
>            Reporter: Knut Anders Hatlen
>         Attachments: Sysfun.java
>
>
> DataDictionaryImpl contains a static field called SYSFUN_AD, which holds an array of
AliasDescriptor objects for the functions in the SYSFUN schema. This array is lazily populated
as the functions are called, and it is shared between all DataDictionaryImpl instances on
the system.
> The AliasDescriptors contain references to the DataDictionaryImpl that created them,
so SYSFUN_AD may end up referencing indirectly to a number of different DataDictionaryImpl
instances, depending on where the respective SYSFUN functions are called the first time. Once
an AliasDescriptor has been added to SYSFUN_AD, it stays there until the DataDictionaryImpl
class is unloaded (in most cases, until the JVM terminates). This means the array may hold
references to DataDictionaryImpl instances that belong to database instances that have been
shut down, and that the memory held by those database instances never becomes eligible for
garbage collection.

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