Tuning of SQL queries requires understanding why DB2 chose a particular access path and determining whether or not that access path should perform as expected. The key to this is understanding what filter factors are, how they are used by the Optimizer and how to get DB2 to better estimate them,
In this article we are going to examine some tuning options that a DBA has available to help improve dynamic SQL performance on DB2 LUW.
I’ve spent the last 17 years teaching SQL Performance & Tuning on DB2 for z/OS. I’ve been trying to get SQL developers to think about the predicates they write from DB2’s perspective instead of what makes sense to humans.
There are numerous enhancements to SQL in DB2 12 for z/OS. There is also a significant amount of SQL performance enhancements in DB2 12 for z/OS which contribute to the “out of the box” savings realized when migrating from DB2 11 for z/OS. The IDUG team explored some of the most significant new SQL
Often times there can 4,5,6 different ways to write an SQL query and get the same results back. What makes one better than any of the others, and is there any ones that are always better, or always worse? Sometimes rewriting 1 predicate in an SQL statement can cause optimization to change. This pres