From: | Andres Freund <andres(at)anarazel(dot)de> |
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To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | pgsql-hackers(at)lists(dot)postgresql(dot)org |
Subject: | Re: Centralizing protective copying of utility statements |
Date: | 2021-06-17 19:23:00 |
Message-ID: | 20210617192300.7gkpqim43gk7ernd@alap3.anarazel.de |
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Lists: | pgsql-hackers |
Hi,
On 2021-06-16 21:39:49 -0400, Tom Lane wrote:
> Although this adds some overhead in the form of copying of
> utility node trees that won't actually mutate during execution,
> I think that won't be too bad because those trees tend to be
> small and hence cheap to copy. The statements that can have
> a lot of substructure usually contain expression trees or the
> like, which do have to be copied for safety. Moreover, we buy
> back a lot of cost by removing pointless copying when we're
> not executing on a cached plan.
Have you evaluated the cost in some form? I don't think it a relevant
cost for most utility statements, but there's a few exceptions that *do*
worry me. In particular, in some workloads transaction statements are
very frequent.
Greetings,
Andres Freund
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