Author Archives

Cardinality Feedback

A fairly important question, and a little surprise, appeared on Oracle-L a couple of days ago. Running 11.2.0.3 a query completed quickly on the first execution then ran very slowly on the second execution because Oracle had used cardinality feedback to change the plan. This shouldn’t really be entirely surprising – if you read all the notes […]

Upgrades

One of the worst problems with upgrades is that things sometimes stop working. A particular nuisance is the execution plan that suddenly stops appearing, to be replaced by an alternative plan that is much less efficient. Apart from the nuisance of the time spent trying to force the old plan to re-appear, plus the time […]

first_rows(10)

No, not the 10th posting about first_rows() this week – whatever it may seem like – just an example that happens to use the “calculate costs for fetching the first 10 rows” optimizer strategy and does it badly. I think it’s a bug, but it’s certainly a defect that is a poster case for the inherent […]

Quiz night

Here’s a little puzzle that came up on OTN recently.  (No prizes for following the URL to find the answer) (Actually, no prizes anyway). There’s more in the original code sample than was really needed, so although I’ve done a basic cut and paste from the original I’ve also eliminated a few lines of the text: […]