Tuning on FromDual GmbH

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.

Binlog format MIXED with filtering

oli.sennhauser@fromdual.com (Oli Sennhauser) — Wed, 15 Jul 2015 06:11:36 +0000

Binlog format MIXED changes the binary log format (ROW or STATEMENT) depending on the queries (deterministic or not). This makes it impossible to define 100% correctly working binary log filter rules.

Flush time is set

oli.sennhauser@fromdual.com (Oli Sennhauser) — Wed, 15 Jul 2015 06:10:36 +0000

If the variable flush_time is set to a non-zero value, all tables are closed (and flushed) every flush_time seconds to disk. This can cause unnecessary and high I/O spikes.

Table definition cache too small

oli.sennhauser@fromdual.com (Oli Sennhauser) — Wed, 15 Jul 2015 06:08:36 +0000

The number of table definitions (SHOW CREATE TABLE<br>G) that can be stored in the table definition cache (table_definition_cache). If you have a large number of tables (
> 400) in your database instance, you should consider a larger table definition cache to increase your database throughput and decrease your query latency.
The command SELECT COUNT(*) FROM information_schema.tables; shows you how many tables and thus table definitions you have. The global status Open_table_definitions is the current amount of open table definitions.

Table open cache too small

oli.sennhauser@fromdual.com (Oli Sennhauser) — Wed, 15 Jul 2015 06:04:36 +0000

The Table Open Cache (table_open_cache or old name table_cache) is a cache to store file handles for all threads. The actual value of cache entries can be seen with the global status of open tables (Open_tables).
Increasing table_open_cache increases the number of file descriptors (open_files_limit) that MySQL requires.
You can check whether you need to increase the Table Open Cache by checking Open_tables and Opened_tables. If the value of Opened_tables is large and you do not use FLUSH TABLES often (which just forces all tables to be closed and reopened), then you should increase the value of the table_open_cache variable.

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).

Impact of column types on MySQL JOIN performance

oli.sennhauser@fromdual.com (Oli Sennhauser) — Wed, 11 Dec 2013 20:12:40 +0000

In our MySQL trainings and consulting engagements we tell our customers always to use the smallest possible data type to get better query performance. Especially for the JOIN columns. This advice is supported as well by the MySQL documentation in the chapter Optimizing Data Types:

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):

Canias optimizations

oli.sennhauser@fromdual.com (Oli Sennhauser) — Wed, 28 Dec 2011 16:02:23 +0000

Canias is a great ERP product but there is still some potential to improve it. We only focus on MyISAM/InnoDB installations of Canias v6.0.2 in this article. For other DB back-ends those recommendations might be obsolete.

Impact of indices on MySQL

oli.sennhauser@fromdual.com (Oli Sennhauser) — Fri, 31 Dec 2010 17:05:17 +0000

It is generally well known that indexes help a lot to speed up database queries (especially SELECT but also UPDATE and DELETE). It is less known, that indexes also have some disadvantages.

MySQL Database Health Check

oli.sennhauser@fromdual.com (Oli Sennhauser) — Sat, 07 Nov 2009 22:13:39 +0000

DBA wisdoms

oli.sennhauser@fromdual.com (Oli Sennhauser) — Mon, 15 Mar 2010 13:29:16 +0000

Controlling developers is like herding cats.

Kevin Loney, Oracle DBA Handbook

Oh no, it's not. It's much harder than that!

Performance Tuning Key for MySQL

oli.sennhauser@fromdual.com (Oli Sennhauser) — Sat, 13 Mar 2010 20:40:21 +0000

This MySQL Performance Tuning Key should give you a guide how to best tune you MySQL database systematically… It should also work similar for other RDBMS.