#InnoDB
MariaDB on defaults — a 128M buffer pool on a 55 GB RAM server
A 16 core server with 55 GB RAM and an SSD, but MariaDB still had the default 128 MB buffer pool. The result was 50 million disk reads in 5 days. The full before-and-after settings, service name and config path traps on DirectAdmin/Debian, rollback steps, and another 500 MyISAM tables waiting for conversion.
One Query Hung for 54 Minutes, Causing Sitewide 504s via MyISAM Locks
A single 30 MB table caused 504s on every page across the site, even with 9.5 GB of RAM still free — I traced information_schema.PROCESSLIST to a single SELECT that had been stuck for 54 minutes on a MyISAM table, cascading into metadata locks across the server, with an immediate fix and ways to prevent it from happening again.
Recover MariaDB Redo Log Corruption with force_recovery and Reinit
MariaDB would not start after an unclean shutdown — a corrupted InnoDB redo log took the mysql.global_priv system table down with it. This is the recovery sequence I actually used, starting with innodb_force_recovery to make the data readable, then dumping each db before reinitializing the whole system, with one rule never to raise force_recovery higher than necessary.