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From "Kathey Marsden (JIRA)" <j...@apache.org>
Subject [jira] [Created] (DERBY-6096) DataTypeDescriptor.estimatedMemoryUsage() has no case for BLOB or CLOB so would underestimate memory usage for those types at zero
Date Mon, 04 Mar 2013 14:15:12 GMT
Kathey Marsden created DERBY-6096:
-------------------------------------

             Summary: 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: 10.8.3.0, 10.9.1.0, 10.7.1.1, 10.6.2.1, 10.5.3.0, 10.4.2.0, 10.3.3.0,
10.2.2.0, 10.1.3.1, 10.10.0.0
            Reporter: Kathey Marsden


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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