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From "Kathey Marsden (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DERBY-6096) OutOfMemoryError with Clob or Blob hash join: DataTypeDescriptor.estimatedMemoryUsage() has no case for BLOB or CLOB so would underestimate memory usage for those types at zero
Date Wed, 06 Mar 2013 21:06:12 GMT

    [ https://issues.apache.org/jira/browse/DERBY-6096?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13595119#comment-13595119
] 

Kathey Marsden commented on DERBY-6096:
---------------------------------------

My thought was to just match the existing entries for LONGVARCHAR_TYPE_ID LONGVARBIT_TYPE_ID
which is:

 /* Who knows? Let's just use some big number */
				return 10000.0;

I see the concern with backporting. Maybe the fix should just go into 10.10 along with a release
note with a  work around for performance issues of setting derby.language.maxMemoryPerTable
higher. Maybe documenting derby.language.maxMemoryPerTable would be good at the same time.
 

                
> OutOfMemoryError with Clob or Blob hash join: DataTypeDescriptor.estimatedMemoryUsage()
 has no case for BLOB or CLOB so would underestimate memory usage for those types at zero
> ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
>
>                 Key: DERBY-6096
>                 URL: https://issues.apache.org/jira/browse/DERBY-6096
>             Project: Derby
>          Issue Type: Bug
>          Components: SQL
>    Affects Versions: 10.1.3.1, 10.2.2.0, 10.3.3.0, 10.4.2.0, 10.5.3.0, 10.6.2.1, 10.7.1.1,
10.9.1.0, 10.10.0.0, 10.8.3.0
>            Reporter: Kathey Marsden
>         Attachments: D6096.java
>
>
> In discussion on derby-dev regarding how much memory is used for hash joins, Knut noted:
> I haven't verified, but I think HashJoinStrategy uses
> DataTypeDescriptor.estimatedMemoryUsage() to estimate how much memory
> the hash table will consume. That method has no case for BLOB or CLOB,
> so it looks as if it will return zero for LOB columns. If that's so, it
> will definitely overestimate how many rows fits in maxMemoryPerTable
> kilobytes if the rows contain LOBs.
> DataTypeDescriptor.estimatedMemoryUsage() should be updated to include BLOB and CLOB
and we should try verify if this theory is correct with a reproduction.

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