8 min read
MySQL 8.0.18 gave us EXPLAIN ANALYZE, and most people read its output wrong. Here is how the per-loop numbers actually work, the misreads I keep seeing, and when the tree format tells the truth tabular EXPLAIN hides.
Database Topic Archive
MySQL Articles
InnoDB internals, replication, locking, query performance, and MySQL operations notes.
7 min read
The MySQL slow query log is still the best forensic record of a bad deploy, but only if you configure it deliberately and digest it into query families. This is the workflow I actually run.
7 min read
When checkpoint age catches up with redo capacity, InnoDB stops the world to flush, and your p99 pays for it. Here is how innodb_redo_log_capacity works in 8.0.30+, how to size it against write bursts, and how furious flushing looks in…
7 min read
GROUP BY, DISTINCT, derived tables, and window functions can all materialize internal temp tables, and when those overflow memory your query is suddenly doing disk I/O nobody planned. Here is how the TempTable engine works and how to find the…
7 min read
One idle REPEATABLE READ session can pin millions of undo records and slowly melt a busy MySQL server. History list length is the canary; this is how to watch it, find the blocker, and keep undo growth under control.
7 min read
Doublewrite exists for one narrow disaster: a torn page that redo cannot repair. This is an honest look at how it works, what it really costs in I/O, how to measure that overhead yourself, and when disabling it is actually…
8 min read
The 75% rule is folklore, not a sizing method. This field guide covers working-set reality, online resizing, warmup dump and restore, and the two counters that actually tell you whether the buffer pool is big enough.