Notes for the problems that show up after launch: bad plans, awkward migrations, index debt, vacuum pressure, replica lag, and the small decisions that make PostgreSQL easier to operate.
SHOW PROCESSLIST is the first thing everyone runs and the most misread output in MySQL operations. Here is what the thread states actually mean, which pileups matter, and how to build a triage habit around performance_schema.threads.
An index-only scan is only index-only when the visibility map says the heap page is all-visible. How to read Heap Fetches in EXPLAIN, build covering indexes with INCLUDE, and keep vacuum honest.
Four hundred requests a minute, three temp tables each: three months later pg_attribute weighed 9 GB with six million dead tuples. Why per-request DDL churns the catalogs, and the patterns that stop it.
A Galera node rejoin either streams a small delta (IST) or copies the entire dataset (SST), and whether any donor's gcache still holds the joiner's missing writesets decides which. Here is how the decision is made, how to size for it, and how to watch it happen.
Btree indexes bloat quietly as updates and deletes churn. Here is how to measure bloat with pgstattuple, why it wrecks cache hit rates, and how REINDEX CONCURRENTLY fixes it without taking the table down.
Every weekday at 9:05 the order system's p99 went from forty milliseconds to eleven seconds, caused by one report holding a twelve-gigabyte memory grant. How grants are sized, how to read the queue in sys.dm_exec_query_memory_grants, and how to fence the pattern.
The order database froze writes for forty-one seconds at peak load because the data file grew by 32 GB and SQL Server zeroed every byte of it first. Percent-growth compounding, Instant File Initialization, and the pre-sizing discipline that makes growth boring.
PgBouncer's transaction pooling mode is the right call for most fleets, but it silently breaks prepared statements, SET, advisory locks, and LISTEN/NOTIFY. Here is how to run it without the 3am surprises.
Debezium tailing a MySQL binlog and a PostgreSQL logical decoding pipeline look similar from Kafka. Underneath, snapshots, schema changes, and retention fail in opposite ways.
Someone forgot the WHERE clause. You can restore last night's backup and replay a day of binlog, or you can generate the inverse transaction and apply it in minutes. Here is how MariaDB flashback actually works.
MySQL hides case behind collations and lower_case_table_names; PostgreSQL makes you choose explicitly. Here are the bugs this difference causes in migrations, and the three fixes that work.
MySQL grew failover tooling around topology repair; PostgreSQL grew it around consensus and leases. Comparing orchestrator and group replication with Patroni and repmgr, honestly.