[hibernate-issues] [Hibernate-JIRA] Commented: (HHH-2470) Use of session.createSQLQuery causes memory leak

[Kiran Hatti (JIRA)]

    [ http://opensource.atlassian.com/projects/hibernate/browse/HHH-2470?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=35242#action_35242 ] 

Kiran Hatti commented on HHH-2470:
----------------------------------

One of the application we worked on uses SQLQuery.addScalar() extensively and we have seen the QueryPlanCache object grow in a duration test. We initially used the hibernate-patch.zip but it didn't work as I was getting NullPointerExceptions. The constructor and the equals method in the patched class NativeSQLQueryScalarReturn were not checking whether the "Type" object was null and this resulted in a NullPointerException when I was using addScalar() method with a single alias parameter (I know, its not a best practice). I used the code in "HHH-2470.patch" which handles the null scenarios for all input objects and it fixed the leak. Without the patch the QueryPlancache grew to about 150 Mb with-in 8 hours. After the fix the QueryPlanCache stayed around 5 MB. Is there anything we can do to get this patch applied to the main branch and possibly provide an "official" patch from Hibernate team.



> Use of session.createSQLQuery causes memory leak 
> -------------------------------------------------
>
>                 Key: HHH-2470
>                 URL: http://opensource.atlassian.com/projects/hibernate/browse/HHH-2470
>             Project: Hibernate Core
>          Issue Type: Patch
>          Components: query-sql
>    Affects Versions: 3.1.3
>         Environment: Win XP, Oracle 10g, Java 1.4.2
>            Reporter: Bjørn Bjerkeli
>            Assignee: Gail Badner
>         Attachments: HHH-2470.patch, hibernate-patch.zip, QueryPlanCacheTest.java, TestCase.zip
>
>
> NativeSQLQuerySpecification fails to properly implement equals and hashcode caused by lacking implementation of hashCode and equals in all SQLQueryReturn implementations and SQLQueryScalarReturn which are members of NativeSQLQuerySpecification. I can see that NativeSQLQuerySpecification has been changed in 3.2, but the problem is still there.
>  
> NativeSQLQuerySpecification instances are used as keys for retrieving and caching NativeSQLQueryPlan instances.
>  
> This causes the caching-mechanism to be pretty useless when Queries created by session.createSQLQuery because new entries will be added all the time in the QueryPlanCache and the SoftLimitMRUCache member.
>  
> So far so good, the more serious problem that is caused by this is stems from the implementation of SoftLimitMRUCache which again uses LRUMap in commons-collection. The put - method of the cache is not treadsafe, and that causes the following fragment in LRUMap to allow the map to grow beyond its maximumSize. That is bacause the containsKey method will return an incorrect result when concurrently updating the map. 
>  
>    public Object put( Object key, Object value ) {
>  
>         int mapSize = size();
>         Object retval = null;
>  
>         if ( mapSize >= maximumSize ) {
>  
>             // don't retire LRU if you are just
>             // updating an existing key
>             if (!containsKey(key)) {
>                 // lets retire the least recently used item in the cache
>                 removeLRU();
>             }
>         }
>  
>         retval = super.put(key,value);
>  
>         return retval;
>     }
>  
> I have included a test-case that demonstrates:
> 1) Wrong implementation of equals and hashCode in NativeSQLQuerySpecification 
> 2) Concurrent use of LRUMap causes the map to grow beyound it's max limit
> 3) Concurrent execution of session.createSQLQuery causes memory leak due to 1) and 2)
>  
> I would be more than happy to contribute to get this fixed. Just let me know.

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