How far can you go with MySQL or MariaDB ?

MySQL theoretical limits are known and they can be found in the manual, they include:

• MyISAM permits data and index files to grow up to 256 TiB by default, but this limit can be changed up to the maximum permissible size of 65,536 TiB (256^7 − 1 bytes).
• The maximum tablespace size depends on the InnoDB page size: 64 TiB for 16 KiB pages.
  (The maximum tablespace size is also the maximum size for a [InnoDB] table.)

But what can be done in practice ?  How far can you go with MySQL or with MariaDB ?

InnoDB Basics - Compaction: when and when not

This is old news for MySQL/MariaDB expert but people that are starting using InnoDB do not always know that disk space is not automatically released when deleting data from a table.  To explain and demonstrate that, I will take two real-world examples: table1 and table2.

Fun with InnoDB Persistent Statistics

Something interesting happened to me in the last days, and it is worth sharing.  I was upgrading MariaDB (MySQL also impacted) to a new major version and mysql_upgrade showed something like this:

[...]
Phase 4/7: Running 'mysql_fix_privilege_tables'
ERROR 1062 (23000) at line 586: Duplicate entry 'schema-table_name#P#partition_name_truncated' for key 'PRIMARY'
ERROR 1062 (23000) at line 590: Duplicate entry 'schema-table_name#P#partition_name_truncated' for key 'PRIMARY'
ERROR 1062 (23000) at line 593: Duplicate entry 'schema-table_name#P#partition_name_truncated' for key 'PRIMARY'
FATAL ERROR: Upgrade failed