Category: Performance

6

When Index Scans Attack!

We all know that table scans can be (but aren’t always) a negative thing. I have spent less time worrying about index scans, though. Index access = good, right? I thought I’d share a recent scenario where an index scan was very expensive. Maybe still better than a table scan, but with one index, I reduced the impact of a...

6

STMM Analysis Tool

I mostly like and use DB2’s Self Tuning Memory Memory Manager (STMM) for my OLTP databases where I have only one DB2 Instance/Database on a database server. I do have some areas that I do not let it set for me. I’ve recently learned about an analysis tool – Adam Storm did a presentation that mentioned it at IDUG 2014...

2

Three Different Ways to Write the Same Join in SQL

This was really a revelation for me when I took DanL‘s SQL workshop before the IDUG conference in Phoenix. I started out as a physical or systems DBA at IBM, and until studying for certification, I hardly wrote a statement more complicated than select * from syscat.bufferpools. After being a DBA for probably 5 years or more I started to...

8

How to Tell When an Index Reorg is Needed

My earlier post on table reorgs covered Reorg’s place in a database maintenance cycle and running reorgchk. If you haven’t already read it, check it out: How to Tell When a Table Reorg is Needed INDEXES After the section on tables, REORGCHK output has a section with details on each index for each table that REORGCHK looked at. The index...

1

Informational Constraints – Benefits and Drawbacks

One of the most frustrating things a DBA can experience is troubleshooting due to bad data. The client is upset because rows are missing or incorrect data is returned.  The client facing web front end could be displaying gobilty-gook because the data retrieved makes no sense. Resources and energy are burned because of an issue is easily solved with the...

9

Redesigning Tablespaces in an Existing Database

Like many applications, WebSphere Commerce puts all tables in USERSPACE1 unless they need larger page sizes. This actually works just fine for smaller and midrange implementations, but we have about one build a year that requires something else – either because of standards that client DBAs adhere to or because they actually are busy enough for I/O and separate buffer...

2

Detailed Analysis of Individual Performance Metrics

Sometimes the things we studied in college are actually useful. As much as I hated my statistics professor, I still learned a lot that I frequently use. Maybe I don’t do many multiple regression problems these days, but I use standard deviation a lot. It is a concept that every DBA or really any IT professional who must analyze performance...