Cost-based optimizer statistics


(Roman Kuzmin) #1

To give cost-based optimizer an idea of table’s cardinality it is recommended to issue queries like this:

CREATE STATISTICS offers_stats ON id FROM offers;

Documentation states that “The cost-based optimizer will not support automated use of statistics during this time period.” Does it mean that I need to periodically issue create statistics statements to update statistics?

I’m asking because if I issue create statistics … queries BEFORE I load my data, optimizer will not use statistics after data is loaded. As the result some joins are very slow.

(Raphael 'kena' Poss) #2

Yes your understanding is correct: the statistics are not currently updated automatically. You need to issue CREATE STATISTICS after the data is loaded, not before.

Good question!

(Roman Kuzmin) #3

Ok, that’s not a problem. But, please, express this limitation more clearly in docs. It seems that optimizer statistics is not documented at all.

Thank you!

(Andy Woods) #4

I’ve filed an issue with our Docs team to update accordingly. Thank you for your feedback!