What the server records.
WHAT LOGS EXIST
The error log The slow query log The general query log The binary log
WHAT THE ERROR LOG CONTAINS
Startup and shutdown Crashes and recovery Warnings and errors
WHY IT IS THE FIRST PLACE TO LOOK
It explains failures to start, and crashes.
WHAT THE SLOW QUERY LOG CONTAINS
Queries exceeding a threshold.
WHAT TO SET THE THRESHOLD TO
Low enough to be useful, and watch its size.
WHAT ELSE TO ENABLE
Logging of queries not using indexes, temporarily.
WHY TEMPORARILY
It is voluminous on a busy server.
WHAT THE GENERAL LOG CONTAINS
Every statement.
WHEN TO USE IT
Briefly, to see exactly what an application sends.
WHY BRIEFLY
It is enormous and costs performance.
WHAT THE BINARY LOG CONTAINS
Every change, for replication and point-in-time recovery.
WHAT TO CONFIGURE
Retention long enough to cover your backups.
WHY THAT MATTERS
Recovery needs logs reaching back to the backup.
WHAT TO MONITOR
Log disk usage.
WHAT COMMONLY FILLS A DISK
Binary logs never expired.
WHAT TO NEVER DO
Delete binary logs by hand while replicas depend on them.
WHAT TO USE INSTEAD
The purge command, which respects that.
