Advice on setting cost for function
От | guyren@relevantlogic.com |
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Тема | Advice on setting cost for function |
Дата | |
Msg-id | 27621de6-c05b-493c-bf53-49539cb04577@Spark обсуждение исходный текст |
Ответы |
Re: Advice on setting cost for function
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Список | pgsql-general |
The documentation in CREATE FUNCTION is fine as far is it goes regarding the COST setting, but that isn’t very far, and I haven’t had any luck finding good advice.
How do I determine what value to set as the COST of a function? I understand that it’s a relative, abstract, per-row sort of thing, but that’s not quite enough to go on to do it well.
If I have a function that looks up a single value from an index, should that be lower than 100? 20, say?
If I have a function that calls multiple other functions, each of which does a reasonable amount of work, should I set the caller to a higher COST, or will Postgres use the costs of the functions it calls?
I can imagine that a SQL function which is just inlined might ignore the COST estimate. Is that so? Are there other such considerations?
In general, a section in the CREATE FUNCTION documentation of two or three paragraphs with a few examples and general guidelines would be very helpful. I would be happy to write it if someone will explain it to me.
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