Query Tuning on FromDual GmbH

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.

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:

Why you should take care of MySQL data types

oli.sennhauser@fromdual.com (Oli Sennhauser) — Wed, 25 May 2016 11:42:20 +0000

A customer reported last month that MySQL does a full table scan (FTS) if a query was filtered by a INT value on a VARCHAR column. First I told him that this is not true any more because MySQL has fixed this behaviour long time ago. He showed me that I was wrong:

Avoid temporary disk tables with MySQL

oli.sennhauser@fromdual.com (Oli Sennhauser) — Fri, 19 Dec 2014 07:38:16 +0000

For processing SELECT queries MySQL needs some times the help of temporary tables. These temporary tables can be created either in memory or on disk.

MySQL single query performance - the truth!

oli.sennhauser@fromdual.com (Oli Sennhauser) — Fri, 13 Dec 2013 17:33:44 +0000

MySQL single query performance - the truth!

As suggested by morgo I did a little test for the same query and the same data-set mentioned in Impact of column types on MySQL JOIN performance but looking into an other dimension: the time (aka MySQL versions).

Do not trust other peoples benchmarks!

oli.sennhauser@fromdual.com (Oli Sennhauser) — Tue, 06 Apr 2021 13:26:06 +0200

Because they do NOT reflect your problems.

One of our customers upgraded last month from MariaDB 10.2 to MariaDB 10.5. In the same change he also converted all his data warehouse (DWH)/BI tables from MyISAM to Aria. An all this, naturally, without testing. And it miserably failed! And then we were under heavy time pressure to make things working again…