October 26, 2026 · QueryKings
A replica broke and you need a new one by morning. Here is how the InnoDB clone plugin, storage snapshots, and mysqldump/mydumper actually compare on wall-clock time, source impact, and binlog retention — and the GTID detail that decides whether the new replica starts cleanly.
Read moreOctober 19, 2026 · QueryKings
The buffer pool is not the whole memory budget. Here is how to account for per-connection buffers, internal temporary tables, and the performance schema, how to read what the server is actually using, and how to size an instance so the kernel never has to choose a victim.
Read moreOctober 12, 2026 · QueryKings
Teams keep their job queue and transactional outbox in MySQL because it keeps the work and the write in one transaction. Here is how SELECT ... FOR UPDATE SKIP LOCKED actually behaves under InnoDB, the index and polling design that keeps it cheap, and the three failure modes it leaves on the table.
Read moreSeptember 21, 2026 · QueryKings
Most MySQL clusters fail over badly the first time it matters for real. Here is what asynchronous, semi-synchronous, and group replication each promise about data loss, how GTIDs and errant transactions decide whether a demoted primary can rejoin, and why the proxy layer — not the database — usually determines your actual outage length.
Read moreSeptember 18, 2026
Before you tune a query you have to pick the right one. How to rank a live workload with performance_schema statement digests, when the slow query log is still the better tool, and why total time beats worst-case latency as a target.
Read moreSeptember 17, 2026 · QueryKings
A 900 GB InnoDB table is not automatically a problem, and partitioning is not automatically the fix. How to tell which of the four real constraints you have hit — buffer pool, DDL time, delete cost, or a single-writer ceiling — and what each one actually calls for.
Read moreSeptember 16, 2026 · QueryKings
One idle transaction left open can slow every read on the server, grow the undo tablespace, and make a routine query plan degrade overnight. Here is how MVCC purge lag builds, how to measure it, and how to keep it from happening again.
Read moreSeptember 15, 2026 · QueryKings
A backup you have never restored is a hypothesis. How to pick between logical dumps, physical snapshots and clones, keep a binlog chain that actually supports point-in-time recovery, and run a timed drill that produces a real RTO number instead of a policy document.
Read moreSeptember 14, 2026
ERROR 1040 is rarely a max_connections problem. How to find the limit that is really binding — memory per connection, thread scheduling, or a slow query holding the pool — and where a pooler like ProxySQL or RDS Proxy helps and where it hides the fault.
Read moreSeptember 11, 2026
Lock wait timeouts and deadlocks are not random. Here is how to read SHOW ENGINE INNODB STATUS and the Performance Schema lock tables, what gap locks and next-key locks actually do under REPEATABLE READ, and the four fixes that hold.
Read moreAugust 18, 2026
Five distinct causes of replica lag — single-threaded apply, giant transactions, missing primary keys, starved replicas, and semi-sync effects — each with a cheap, decisive test and its actual fix.
Read moreJuly 21, 2026
INSTANT DDL, native INPLACE, gh-ost, or pt-online-schema-change? A decision tree for zero-downtime schema changes — including the metadata-lock trap that makes "non-blocking" DDL block everything.
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