Category: Performance

5

Clustering a Table on an Index

I have been playing a fair amount lately with clustering indexes and have been rehashing my views on reorging tables on an index. This is still a work in progress, but thought I’d share some details and see if others out there have any thoughts to share with me and others on it. Clustering a Table on an Index I’ve...

1

Example of A Clustering Low-Cardinality Index Helping Query Performance

The request from the developers was something along the lines of “Help, Ember, this query needs to perform better”. Sometimes the query I’m working on is not one that shows up as a problem from the database administrator’s perspective, but one that is especially important in some part of application functioning. In this case, this query is related to the...

3

HADR Tools: the HADR Simulator

I have not made extensive use of the HADR Tools that IBM offers in the past. Most of my HADR setups to date have either been same-data-center using NEARSYNC or have used ASYNC to copy data between data centers. I haven’t had much cause to tweak my network settings or change my SYNCMODE settings based on hardware/networking. However, I have...

4

DB2 Basics: db2top

There are a lot of things I can cover on db2top, and probably more tips and tricks using db2top than many other tools out there. Searching the web on db2top gets more good results than on many other db2 topics. I thought I’d start with some of the basics. Using db2top requires some general knowledge of how db2 works. I...

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...