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Posted to derby-dev@db.apache.org by "Rick Hillegas (JIRA)" <de...@db.apache.org> on 2006/09/19 16:53:23 UTC
[jira] Updated: (DERBY-1397) Tuning Guide: Puzzling optimizer
documentation
[ http://issues.apache.org/jira/browse/DERBY-1397?page=all ]
Rick Hillegas updated DERBY-1397:
---------------------------------
Fix Version/s: 10.2.2.0
(was: 10.2.1.0)
Moving to 10.2.2.0.
> Tuning Guide: Puzzling optimizer documentation
> ----------------------------------------------
>
> Key: DERBY-1397
> URL: http://issues.apache.org/jira/browse/DERBY-1397
> Project: Derby
> Issue Type: Bug
> Components: Documentation
> Affects Versions: 10.2.1.0
> Reporter: Rick Hillegas
> Assigned To: Laura Stewart
> Fix For: 10.2.2.0
>
>
> Selectivity and cardinality statistics
> Working with cardinality statistics
> When cardinality statistics are automatically updated
> "For other operations, Derby automatically updates statistics for the table and all indexes on the table if they are already exist. Those operations are:
> * (all indexes) When you execute SYSCS_UTIL.SYSCS_COMPRESS_TABLE.
> * (index only) When you drop a column that is part of a table's index; the statistics for the affected index are dropped, and statistics for the other indexes on the table are updated.
> "
> What does the second bullet mean? Derby doesn't let you drop a column from a table right now.
> ----------------------------------------------------------
> Here's another puzzling piece of optimizer documentation:
> I'm puzzled by the following paragraph in Tuning Guide->DML statements and performance->Performance and optimization->Joins and performance->Join strategies:
> "If memory use is not a problem for your environment, set this property to a high number; allowing the optimizer the maximum flexibility in considering a join strategy queries involving large queries leads to better performance. It can also be set to smaller values for more limited environments."
> I can't find the name of this property on that page of the Tuning Guide. I'm also confused about what we consider to be a "high number" versus what we consider to be "smaller values". Would appreciate advice here.
> Satheesh adds this:
> The property it may be referring to is
> *derby.language.maxMemoryPerTable*. The default value is 1024 KB.
> Current default value is too small, so it would be a good tip for
> developers to know and tune this property. It would be great if Derby
> can configure this property value based on factors like max heap size,
> size of data cache and/or other parameters.
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