3409
MariaDBERRORCommonForeign KeysHIGH confidence
Failed to add foreign key to system tables
Production Risk
High — data dictionary may be in an inconsistent state.
How to reproduce
trigger — this will error
trigger — this will error
ALTER TABLE child ADD FOREIGN KEY (col) REFERENCES parent(id);
expected output
ERROR 3409 (HY000): Failed to add foreign key to system tables.
Fix
Check error log and run InnoDB diagnostics
Check error log and run InnoDB diagnostics
SHOW ENGINE INNODB STATUS; CHECK TABLE child; CHECK TABLE parent;
Why this works
INNODB STATUS provides details about the internal failure and CHECK TABLE validates structural integrity.
What not to do
✕
Sources
Official documentation ↗
MySQL 8.0 — 3409 ER_FK_FAIL_ADD_SYSTEM
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