[ http://issues.apache.org/jira/browse/DERBY-1397?page=all ]
Rick Hillegas updated DERBY-1397: --------------------------------- Fix Version/s: 10.2.3.0 (was: 10.2.2.0) Move to 10.2.3.0. > 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: 10.2.1.6 > Reporter: Rick Hillegas > Fix For: 10.2.3.0 > > > 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. -- 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