Notes for the problems that show up after launch: bad plans, awkward migrations, index debt, vacuum pressure, replica lag, and the small decisions that keep PostgreSQL, MySQL, MariaDB, and SQL Server easier to operate.
Find the queries dragging your Postgres down, read their plans, and fix them in order of impact.
Read the guide →Which indexes to add, which to drop, and how to spot redundant index debt before it costs you writes.
Read the guide →How autovacuum works, when it falls behind, and how to keep bloat from eating your storage and your buffer cache.
Read the guide →Sizing pools, PgBouncer modes, and how to stop idle-in-transaction sessions from exhausting max_connections.
Read the guide →Track lag, WAL throughput, and replication slots before they turn into stale reads or a full disk.
Read the guide →
Backups, restores, PITR, archive gaps, and recovery drills for PostgreSQL.
AWS RDS, Azure Database for PostgreSQL, Google Cloud SQL, AlloyDB, and managed PostgreSQL monitoring notes.
Connection storms, pool saturation, PgBouncer behavior, and max_connections pressure.
CPU, memory, disk, temp files, checkpoints, buffers, and workload pressure.
Index design, index debt, reindexing, constraint indexes, and evidence-driven DDL.
Lock waits, deadlocks, blocking chains, idle transactions, and transaction hygiene.
Galera clustering, InnoDB and Aria internals, replication, optimizer behavior, and MariaDB operations notes.
InnoDB internals, replication, locking, query performance, and MySQL operations notes.
HNSW, IVFFlat, recall, embedding search, and production RAG performance notes.
Replica lag, WAL growth, failover readiness, hot standby behavior, and replication slots.
Query plans, EXPLAIN ANALYZE, planner regressions, pagination, joins, and statistics.
Wait statistics, tempdb, Query Store, Always On availability groups, and SQL Server operations notes.
Autovacuum, dead tuples, bloat, wraparound, MVCC, freeze age, and visibility.
The most informative crash I ever debugged had an empty error log — mysqld was OOM-killed, and the silence was the clue. What changed in 8.0's log format, which warning lines deserve a page, and how to read crash recovery.
A runaway UPDATE joined wrong scanned for three hours on MySQL because max_execution_time only applies to SELECT, while on PostgreSQL the same class of bug dies at statement_timeout. But PostgreSQL's timeout also kills your maintenance VACUUM if you set it…
One month-end report held a read view for eleven hours, and the undo tablespaces grew by 38GB that never came back on their own. What undo logs store, how purge gets pinned, and the truncate surgery that reclaims the disk.
Fifty thousand tenant tables against a 4,000-entry table cache meant thousands of handle opens per second and a CPU-bound server. What the counters said, how we sized table_open_cache and table_definition_cache, and why the schema still had to change.
A nightly import of 380M rows spent more time merging the change buffer than inserting rows. What the change buffer defers, why unique indexes opt out, the two knobs that control it, and which workloads should disable it.
After an audit flipped sync_binlog from 0 to 1, every commit on an order cluster queued behind a binlog fsync and p99 commit latency went from 3ms to 41ms. A 1000-microsecond group-commit delay batched the fsyncs and brought p99 back…
A session-token table serving 52,000 point selects a second stalled on the btr_search latch for minutes at a time. What the adaptive hash index really is, how to see the contention, and how to test turning it off without guessing.
A nightly aggregation wrote 4.1GB of temp files on PostgreSQL and nobody noticed until the disk alert; on MySQL the same class of query pushed Created_tmp_disk_tables up 40,000 an hour. Here is when each engine spills, how to see it,…
We rewrote a 410-million-row table for an unrelated ALTER and reordered its columns while we were at it — the heap shrank 11 percent, 7 GB, with zero schema-visible change. The alignment math, the measurement method, and when it is…
An hourly REFRESH MATERIALIZED VIEW took an ACCESS EXCLUSIVE lock and blacked out a dashboard for eleven minutes every hour, while the MySQL original used a cron-maintained summary table that had been silently stale for weeks. Here is how each…