Re: Terribly slow query with very good plan? - Mailing list pgsql-performance

From Les
Subject Re: Terribly slow query with very good plan?
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Msg-id CAKXe9UA_E99+E3rL45PtXR5fCkZA+ttj8o5oKAQMqmrn5c4=PA@mail.gmail.com
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In response to Re: Terribly slow query with very good plan?  (Les <nagylzs@gmail.com>)
Responses Re: Terribly slow query with very good plan?  (Les <nagylzs@gmail.com>)
Re: Terribly slow query with very good plan?  (Nick Cleaton <nick@cleaton.net>)
List pgsql-performance

In the fast case the 'Felhasználók%' part is known at query planning
time, so it can be a prefix search.

In the slow case, the planner doesn't know what that value will be, it
could be something that starts with '%' for example.


First of all, it CANNOT start with '%'. This is a fact and this fact can be determined by analyzing the query. Something that the query planner should do, right?

Second argument: the same query is also slow with the ^@ operator...

Oh I see, the query planner does not know that there will be no % characters in file and folder names.

But what is the solution then? It just seems wrong that I can speed up a query 1000 times by replacing it with a nested loop in a pl/sql function :(

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