Re: Use of * affect the performance

От: Qingqing Zhou
Тема: Re: Use of * affect the performance
Дата: ,
Msg-id: dqh4lf$2o66$1@news.hub.org
(см: обсуждение, исходный текст)
Ответ на: Use of * affect the performance  (Marcos)
Список: pgsql-performance

"Marcos" <> wrote
>
> I always think that use of * in SELECT affected in the performance,
> becoming the search slowest.
>
> But I read in the a Postgres book's that it increases the speed of
> search.
>
> And now???? What the more fast?
>

If you mean use "*" vs. "explicitely name all columns of a relation", then
there is almost no difference except the negligible difference in parsing.
If you mean you just want part of the columns of a relation but you still
use "*": Yes, you will save one projection operation for each result row but
you will pay for more network traffic. In the worst case, say your "*"
involves some toast attributes, you just hurt performance. Considering the
benefits is so marginal and dangerous, I suggest stay with the idea that
"only retrive the columns that you are interested in".

Regards,
Qingqing




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