DB2 - Problembeschreibung
Problem IT01092 | Status: Geschlossen |
QUERY PERFORMANCE CAN SUFFER DUE TO INCORRECT INDEX SCAN COST CALCULATION ON DB210 ( LUW ) RELEASES | |
Produkt: | |
DB2 FOR LUW / DB2FORLUW / A50 - DB2 | |
Problembeschreibung: | |
Optimizer can choose a wrong index due to incorrect index scan cost calculation. This code was introduced due to the jump scan feature introduced from DB2 v10.1 onwards hence this defect can be hit only in DB2 v10 releases. There are a few pre-conditions for this defect to be hit. They are: a) the query includes a join between two tables on 2 or more columns that are statistically correlated b) there is an index that can apply the join preds as start and stop keys c) the query includes one or more local predicates on the join columns (it is more likely to be hit for equality local preds) Symptoms can be an upgrade is performed from v9.5, v9.7 to v10.1 or v10.5 and overall performance is slow due to pre-dominance of above kind of queries running in the database. No obvious bottlenecks will be visible in the database and it'll show that its working but plan changes will happen which will make the optimizer choose a wrong index and make it run longer and read abnormal amount of rows. Due to the new code introduced for jump-scan, this caused a regression in the index-scan costing calculation. | |
Problem-Zusammenfassung: | |
**************************************************************** * USERS AFFECTED: * * All DB2 v10.5 customers with low cardinality estimates, * * mixed index applied local and join predicates. * **************************************************************** * PROBLEM DESCRIPTION: * * See Error Description * **************************************************************** * RECOMMENDATION: * * Customers experiencing this issue should upgrade to DB2 * * Cancun Release 10.5.0.4 or higher. * **************************************************************** | |
Local-Fix: | |
Workaround ============ If there are not many queries like this, a) collect a column group statistic on the join predicate columns not referenced by equality predicates; or b) apply an optimization profile to specify the desired index access | |
verfügbare FixPacks: | |
DB2 Cancun Release 10.5.0.4 (also known as Fix Pack 4) for Linux, UNIX, and Windows | |
Lösung | |
DB2 Cancun Release 10.5.0.4 and higher contains this fix. After upgrading, customer should see higher cardinality estimates, when the appropriate Column Group Statistics have been gathered using runstats. | |
Workaround | |
keiner bekannt / siehe Local-Fix | |
Weitere Daten | |
Datum - Problem gemeldet : Datum - Problem geschlossen : Datum - der letzten Änderung: | 16.04.2014 10.11.2014 10.11.2014 |
Problem behoben ab folgender Versionen (IBM BugInfos) | |
Problem behoben lt. FixList in der Version | |
10.5.0.4 |