Survivor: MySQL Island – Outwit, Outplay, Outlast Metadata...
summary
Migration from MySQL 5.7 to 8.0 exposes a change: creating a child table with a foreign key requests an exclusive MDL on the parent that can block otherwise-compatible reads, and on RDS this shows as a Performance Insights MDL weight event and produced a ~1 minute outage at Capsule. Reproduceable behavior is captured by a GitHub test script that runs concurrent sessions and inspects metadata_locks; mitigation options shown include monitoring active threads, reviewing FK use, online schema tools, and adjusting the session max_lock_weight timeout.
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chapters (8)
- 0:00Metadata locks in MySQL
- 3:06Data vs metadata locks
- 6:23Metadata lock scenario one
- 11:17Scenario two with foreign key constraints
- 14:30Real-world impact on application performance
- 17:21MySQL 5.7 vs 8.0 differences
- 18:25Preventing metadata lock issues
- 20:35Q&A
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