Optimizer on FromDual GmbH

Comparing Optimizer Results

oli.sennhauser@fromdual.com (Oli Sennhauser) — Fri, 18 Nov 2022 10:59:18 +0000

A while ago I read a paper about Optimizer Benchmarks: How Good Are Query Optimizers, Really? by Viktor Leis from Fakultät für Informatik of the Technische Universität München.

SQL Query Tuning - Performance

oli.sennhauser@fromdual.com (Oli Sennhauser) — Mon, 05 Oct 2020 16:13:10 +0000

How could the following SQL queries be improved performance wise and otherwise and can you also explain why your change is more optimal?

Creating synthetic data sets for tuning SQL queries

oli.sennhauser@fromdual.com (Oli Sennhauser) — Fri, 02 Oct 2020 16:50:33 +0000

When it comes to SQL Query tuning with customers we often get the slow running SQL query and possibly, in good cases, also the table structure. But very often, for various reasons, we do not get the data.

MariaDB indexing of NULL values

oli.sennhauser@fromdual.com (Oli Sennhauser) — Thu, 29 Nov 2018 20:10:55 +0000

In the recent MariaDB DBA advanced training class the question came up if MariaDB can make use of an index when searching for NULL values… And to be honest I was not sure any more. So instead of reading boring documentation I did some little tests:

Find evil developer habits with log_queries_not_using_indexes

oli.sennhauser@fromdual.com (Oli Sennhauser) — Wed, 20 Sep 2017 16:00:03 +0000

Recently I switched on the MariaDB slow query logging flag log_queries_not_using_indexes just for curiosity on one of our customers systems:

Deadlocks, indexing and Primary Key's

oli.sennhauser@fromdual.com (Oli Sennhauser) — Thu, 16 Aug 2012 10:51:40 +0000

Recently a customer has shown up with some deadlocks occurring frequently. They were of the following type (I have shortened the output a bit):

How the MySQL Optimizer with MySQL Cluster is cheating you...

oli.sennhauser@fromdual.com (Oli Sennhauser) — Mon, 17 May 2010 20:10:23 +0000

At a customer we had a nice example of how the MySQL Optimizer is cheating when used in combination with the MySQL Cluster. The customer had queries running not too slow in the development environment but when he tried them on the acceptance test environment (with more data) the query was running much too long which was unacceptable because this query can occur many times per second.