Re: [PERFORM] optimizing immutable vs. stable function calls?

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От Karl Czajkowski
Тема Re: [PERFORM] optimizing immutable vs. stable function calls?
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Msg-id 20170119024512.GE23081@moraine.isi.edu
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Ответ на Re: [PERFORM] optimizing immutable vs. stable function calls?  (Tom Lane)
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Re: [PERFORM] optimizing immutable vs. stable function calls?  (Tom Lane, )
 Re: [PERFORM] optimizing immutable vs. stable function calls?  ("David G. Johnston", )
  Re: [PERFORM] optimizing immutable vs. stable function calls?  (Tom Lane, )
   Re: [PERFORM] optimizing immutable vs. stable function calls?  ("David G. Johnston", )
    Re: [PERFORM] optimizing immutable vs. stable function calls?  (Jim Nasby, )
     Re: [PERFORM] optimizing immutable vs. stable function calls?  (Merlin Moncure, )
 Re: [PERFORM] optimizing immutable vs. stable function calls?  (Tom Lane, )
  Re: [PERFORM] optimizing immutable vs. stable function calls?  (Karl Czajkowski, )
 Re: [PERFORM] optimizing immutable vs. stable function calls?  (Karl Czajkowski, )
On Jan 18, Tom Lane modulated:
> Karl Czajkowski <> writes:
> > Is there a correctness hazard with pretending our function is
> > IMMUTABLE, even though we will change the underlying config parameter
> > in the same connection?
>
> You could probably get away with that if you never ever use prepared
> queries (beware that almost anything in plpgsql is a prepared query).
> It's a trick that's likely to bite you eventually though.
>

That sounds unnerving. I think I need to play it safe. :-/

Does the plan cache disappear with each connection/backend process?
Or is there also a risk of plans being shared between backends?

Would it be invasive or a small hack to have something like
"transaction-immutable" which can be precomputed during planning, like
immutable, but then must discard those plans at the end of the
transaction...?


karl



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