Optimize

The last time I consulted a customer, he came up to me beaming with joy and said that he had taken my advice and changed all the primary key columns from BIGINT (8 bytes) to INT (4 bytes) and that had made a big difference! His MySQL 8.4 database is now 750 Gbyte smaller (from 5.5 Tbyte). Nice!

And yes, I know that contradicts the recommendations of some of my PostgreSQL colleagues (here and here). In the MySQL world, more emphasis is placed on such things (source):

Use the most efficient (smallest) data …

As we already stated in earlier articles in this blog
[1 and 2
] it is a good idea to use NULL values properly in MariaDB and MySQL.

One of my Mantras in MariaDB performance tuning is: Smaller tables lead to faster queries! One consequence out of this is to store NULL values instead of some dummy values into the columns if the value is not known (NULL: undefined/unknown).

To show how this helps related to space used by a table we created a little example:

CREATE TABLE big_null1 (
  id INT UNSIGNED NOT NULL …

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 …