A large-ish customer in banking (largest tables on that particular system: ~1 billion rows) once decided to separate the OLTP database from the "log database" in order to better use resources and prevent contention on some tables, as the append-only log database is used heavily for analytic querying of all sorts. That seems to make … Continue reading The Difficulty of Tuning Queries Over a Database Link – Or How I Learned to Stop Worrying and Love the DUAL@LINK Table
Tag: SQL tuning
NOT IN vs. NOT EXISTS vs. LEFT JOIN / IS NULL: MySQL
When you're spoiled with Oracle's fabulous query transformation capabilities and its really well-done cost-based optimiser, then you might forget how difficult SQL query tuning used to be in the "old days" or with those less sophisticated databases. Here's a really nice explanation of the various means of implementing an ANTI-JOIN in MySQL: http://explainextended.com/2009/09/18/not-in-vs-not-exists-vs-left-join-is-null-mysql/