Query Performance Analysis

Some of the more complicated work a DBA does is often analyzing a query. Whether it is proactive or in response to a performance problem, there are so many factors that go into query performance. Even when looking at a query that has a performance problem, there is only occasionally a single, obvious cause for all of the problems.… Read the rest

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Funny SQL I Have Seen Lately

I’ve run across a few strange SQL statements lately, and while the mistakes they make are not the most impactful, I thought I’d share how I think they could be better written.

Unnecessary use of a Common Table Expression

This query isn’t really wrong, it just doesn’t make much sense.… Read the rest

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Using DB2’s ADMIN_MOVE_TABLE to Move Tables from One Tablespace to Another

What is ADMIN_MOVE_TABLE

ADMIN_MOVE_TABLE is an administrative stored procedure introduced in DB2 9.7. The intent is to provide a tool that can be used to perform an online move of a table, while transactions are still occurring against the table. Moves can be used to change what tablespace a table is in, convert a table to MDC, change the table name, perform several changes that would normally require reorgs, reduce the size of a column, and perform other changes.… Read the rest

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A Faster Way of Joining When Applying a Distinct

I have been paying a bit of attention to cross-platform SQL optimization lately, and read this interesting post:
https://www.periscopedata.com/blog/use-subqueries-to-count-distinct-50x-faster.html?utm_content=bufferaf11f&utm_medium=social&utm_source=linkedin.com&utm_campaign=buffer

Being a bit of an experimenter, the first thing that I wondered is how DB2 would handle this scenario. Would the DB2 optimizer be smarter than others, or would the same hold true for DB2 that held true for PostgreSQL?… Read the rest

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Multiple Index Regression Analysis

I actually had a blog entry started on this topic before IDUG. I knew this was possible, but not exactly how to do it. Then I sat in Scott Hayes’ session – D04 – More Sage Advice: Invaluable DB2 LUW Performance Insights from Around the Globe, and he had all the details I needed to really get rolling on trying this out – saving me valuable time in research.… Read the rest

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