On 2021-05-29 03:40, Lionel Bouton
wrote:
Le 29/05/2021 à 02:38, Dean Gibson (DB Administrator) a écrit :
The original VACUUM FULL ANALYZE ran in 10 hours. The plain ANALYZE ran in 88 seconds.
One possibility is that your data has a distribution that defeats the ANALYZE sampling strategy.
If that is the case you can force ANALYZE to do a better job by increasing the default_statistics_target value (100 by default) and reload the configuration. This will sample more data from your table which should help the planner find out what the value distribution looks like for a column and why using an index for conditions involving it is a better solution.
The last time I had to use this setting to solve this kind of problem I ended with :
default_statistics_target = 500
But obviously the value suited to your case could be different (I'd increase it until the planner uses the correct index). Note that increasing it increases the costs of maintaining statistics (so you don't want to increase this by several orders of magnitude blindly) but the default value seems fairly conservative to me.
For reference and more fine-tuned settings using per table statistics configuration and multi-column statistics for complex situations, see :
- https://www.postgresql.org/docs/13/runtime-config-query.html
- https://www.postgresql.org/docs/13/planner-stats.html
-- Lionel Bouton gérant de JTEK SARL https://www.linkedin.com/in/lionelbouton/
