Db2 Experts on a Data Science Quest
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… Read the rest
This technote caught my eye when @db2_support tweeted it the other day ago. It was titled as “DB2 might choose a sub-optimal query execution plan due to distribution statistics”. The title alone intrigued me. As I read through, I thought that I needed to do a bit of investigation to better understand the issue.… Read the rest
Continue reading »When does case matter in DB2? Well, it doesn’t unless it does. Nice and clear, huh?
Text must be in the correct case whenever it is part of a literal string. Things that you have to enclose in single quotes are case sensative.… Read the rest
Continue reading »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 pools to matter.… Read the rest
There are a a vast array of things you can do in SQL. But just because you can doesn’t always mean that you should.
I recently ran into an interesting situation with FETCH FIRST ROW ONLY.
The day after new code was deployed, a production database system that usually runs with 40% CPU utilization or less was suddenly pegged at 100% CPU utilization.… Read the rest
Continue reading »Sometimes just using the index advisor and a bit of common sense, you can address SQL performance issues. But other times, you have to dig a bit deeper.
I recently found the following query and 300 of its closest cousins (differing only in the length of the second in-list) were eating 30% of the CPU time used by queries on a rather busy database.… Read the rest
Continue reading »Recently, I needed to do some SQL profiling – discovering exactly what SQL a web application was executing against the database. I learned a lot, and when I learn a lot, I try to share with my readers.
I went into this exercise with two major misconceptions:
I had the first misconception proven wrong pretty immediately.… Read the rest
Continue reading »One of the top SQL tips on many lists for developers of SQL is to avoid applying a function to the table data. I think of this as avoiding funcitons on the left of my comparison operator (=, !=, , <, etc) – though that’s a simplification that may not always be correct.… Read the rest
Continue reading »Many times, the SQL analysis I do is extremely focused – mostly on SQL that is a proven resource hog or a suspected problem. Analyzing all SQL used in a particular process can be a bit different, and may not be something that is frequently done in WebSphere Commerce databases.… Read the rest
Continue reading »This series started with Explain Part 1 – Explain and the DB2 Optimizer. This is the second post in the series. I want to cover my favorite method for generating Explain Plans, and in the process, discuss some of the elements.… Read the rest
Continue reading »Generating an Explain Plan is easy…
Properly reading an Explain Plan is harder…
Taking appropriate action is harder still.
When I started my career as a physical DBA with IBM Global Services, generating Explain Plans or even general analysis of SQL was not really a part of my job description.… Read the rest
Continue reading »I haven’t generally been known for my SQL tips. I can find my way around SQL decently enough, but for years, I didn’t do much of it. I’ve used it more and more as the years have gone by as I have moved out of a stictly physical/system DBA role and into a more mixed role where I interact and collaborate with our development team.… Read the rest
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