multiple table scan performance
| От | Samuel Gendler |
|---|---|
| Тема | multiple table scan performance |
| Дата | |
| Msg-id | AANLkTim2zSEznvRPJNqrDTfTmgRNCBWZs1KpdjTGEOL2@mail.gmail.com обсуждение исходный текст |
| Ответы |
Re: multiple table scan performance
Re: multiple table scan performance Re: multiple table scan performance |
| Список | pgsql-performance |
I've got some functionality that necessarily must scan a relatively large table. Even worse, the total workload is actually 3 similar, but different queries, each of which requires a table scan. They all have a resultset that has the same structure, and all get inserted into a temp table. Is there any performance benefit to revamping the workload such that it issues a single:
insert into (...) select ... UNION select ... UNION select
as opposed to 3 separate "insert into () select ..." statements.
I could figure it out empirically, but the queries are really slow on my dev laptop and I don't have access to the staging system at the moment. Also, it requires revamping a fair bit of code, so I figured it never hurts to ask. I don't have a sense of whether postgres is able to parallelize multiple subqueries via a single scan
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