db-derby-dev mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Rick Hillegas (JIRA)" <derby-...@db.apache.org>
Subject [jira] Updated: (DERBY-1397) Tuning Guide: Puzzling optimizer documentation
Date Tue, 19 Sep 2006 14:53:23 GMT
     [ http://issues.apache.org/jira/browse/DERBY-1397?page=all ]

Rick Hillegas updated DERBY-1397:

    Fix Version/s:

Moving to

> 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:
>            Reporter: Rick Hillegas
>         Assigned To: Laura Stewart
>             Fix For:
>  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
> "
> What does the second bullet mean? Derby doesn't let you drop a column from a table right
> ----------------------------------------------------------
> 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
> 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.

This message is automatically generated by JIRA.
If you think it was sent incorrectly contact one of the administrators: http://issues.apache.org/jira/secure/Administrators.jspa
For more information on JIRA, see: http://www.atlassian.com/software/jira


View raw message