When a small self-hosted service lost its disk, we restored the MySQL Docker volume from last night's tar backup, and MySQL refused to start with InnoDB corruption errors. The backup had been a file copy of a running database. How we recovered from an older dump, and the backup approach and restore drills we use now.
Postgres and MySQL both speak SQL, but their internals push applications in different directions. We compare connections, MVCC and cleanup, clustered versus heap storage, and replication, and list what each difference changes in your code and operations.
A one-second ALTER TABLE ... ALGORITHM=INSTANT hung for 11 minutes and every query on the table queued behind it. The blocker was a reporting job holding an open transaction. How we found it with performance_schema and made migrations fail fast.
Stock updates from supplier feeds started failing with Deadlock found when trying to get lock during peak hours. Concurrent upsert batches touched the same unique keys in different orders under InnoDB next-key locking. Sorting, smaller batches and a retry fixed it.