Horton

Re: Centralizing protective copying of utility statements

Andres Freund <andres@anarazel.de>

View thread View on postgr.es
From: Andres Freund <andres@anarazel.de>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-hackers@lists.postgresql.org
Date: 2021-06-17T19:23:00Z
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

Commits

  1. Avoid scribbling on input node tree in CREATE/ALTER DOMAIN.

  2. Centralize the logic for protective copying of utility statements.