Have you ever looked at a list of tables in your database, only to see the set of EXPLAIN tables present in two, five or even 10 different developers’ schemas?
I don’t know about you, but this drives me crazy.… Read the rest
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Tag: SQL
DB2 Administrative SQL Cookbook: Looking at How Current Statistics Are
Current statistics are vital to performance. If I’m encountering a database I haven’t regularly been supporting, and don’t know the maintenance plans and schedules, I frequently query to get an idea of how current they are.
Purpose
To report the dates of statistics collection and the number of tables statistics were collected for on each date.… Read the rest
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DB2 Basics: Administrative Commands
I had been in conversation with a respected DBA who is a well known speaker and author. I had mentioned how difficult it is to come up with advanced topics to write and speak about. That is when he responded “Advanced topics only narrow the audience”.… Read the rest
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DB2 Administrative SQL Cookbook: Finding Problem SQL in the Package Cache
I wrote a developerWorks article on finding problem SQL in your package cache. But I refine and play with my SQL over time, so I thought I’d share the version I’ve been using recently.
Purpose
To find problem SQL in the Package Cache across several importance performance categories.… Read the rest
Continue reading »Using LISTAGG to Turn Rows of Data into a Comma Separated List
This is a topic I have to look up from time to time, and I always go straight to Serge Rielau’s blog. He has a number of good articles on LISTAGG, the similar XML specific functions, and much more.
While he’s already covered the topic in great detail, I thought I’d add my own way of looking at it, and a use case or two for DB2 System views.… Read the rest
Continue reading »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.… Read the rest
Continue reading »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… Read the rest
Runstats Issue With Columns Where There is a Long Common Prefix in Character Data
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 »DB2 Basics: Capitalization
When does case matter in DB2? Well, it doesn’t unless it does. Nice and clear, huh?
When Text Must be in the Correct Case
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 »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 pools to matter.… Read the rest
The Danger of FETCH FIRST ROW ONLY
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.
How the Problem Manifested
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 »Using a Statistical View to Improve Query Performance
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
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