| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> |
| Cc: | Bryn Llewellyn <bryn(at)yugabyte(dot)com>, "David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com>, Christophe Pettus <xof(at)thebuild(dot)com>, pgsql-general list <pgsql-general(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: User's responsibility when using a chain of "immutable" functions? |
| Date: | 2022-06-29 06:29:38 |
| Message-ID: | 2997974.1656484178@sss.pgh.pa.us |
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| Lists: | pgsql-general |
Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> writes:
> st 29. 6. 2022 v 7:46 odesílatel Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> napsal:
>> ... that result has discouraged most people from spending much
>> time on mechanically checking such things. If you declare a function
>> immutable, Postgres will believe you; the consequences if you lied
>> are on your own head.
> We cannot ensure that the function is immutable, but we can detect that the
> function is not very probably immutable (in execution time).
Sure, there are a lot of easy cases where we could say "that's
obviously not immutable". But is it worth spending engineering
effort and runtime on that? I suspect the cases that people
might actually mess up are less obvious, so that we might
accomplish little more than offering a false sense of security.
regards, tom lane
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