When data goes wrong.
WHAT CAUSES IT
Unclean shutdown Failing storage Memory faults Copying data files while running Software defects
WHAT THE SYMPTOMS ARE
Errors on specific tables Crashes on particular queries Results that are plainly wrong
WHAT TO DO FIRST
Stop writing to it.
WHY
Continuing can spread the damage.
WHAT TO DO SECOND
Take a copy of the current state.
WHY BEFORE ANY REPAIR
Repair tools can make things worse, and the copy preserves options.
WHAT CHECK COMMANDS PROVIDE
Confirmation of which tables are affected.
WHAT REPAIR COMMANDS DO
Attempt to rebuild structures, sometimes discarding rows.
WHY THAT IS A LAST RESORT
Data is lost silently.
WHAT TO PREFER
Restoring from backup.
WHY
It is a known-good state, rather than a guess.
WHAT TO INVESTIGATE AFTERWARDS
Why it happened.
WHY THAT MATTERS MOST
Failing storage produces corruption again, on the restored copy.
WHAT TO CHECK
Disk health System logs for input and output errors Memory
WHAT TO DO IF HARDWARE IS SUSPECT
Move to different hardware before restoring.
WHAT TO VERIFY AFTER RECOVERY
Row counts, and application behaviour.
