Re: Slow query, where am I going wrong?
| От | Albe Laurenz |
|---|---|
| Тема | Re: Slow query, where am I going wrong? |
| Дата | |
| Msg-id | D960CB61B694CF459DCFB4B0128514C208A4E327@exadv11.host.magwien.gv.at обсуждение исходный текст |
| Ответ на | Re: Slow query, where am I going wrong? (AndyG <andy.gumbrecht@orprovision.com>) |
| Ответы |
Re: Slow query, where am I going wrong?
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| Список | pgsql-performance |
> But why? Is there a way to force the planner into this? I don't know enough about the planner to answer the "why", but the root of the problem seems to be the mis-estimate for the join between test_result and recipe_version (1348 instead of 21983 rows). That makes the planner think that a nested loop join would be cheaper, but it really is not. I had hoped that improving statistics would improve that estimate. The only way to force the planner to do it that way is to set enable_nestloop=off, but only for that one query. And even that is a bad idea, because for different constant values or when the table data change, a nested loop join might actually be the best choice. I don't know how to solve that problem. Yours, Laurenz Albe
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