From: | Andres Freund <andres(at)anarazel(dot)de> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | David Rowley <david(dot)rowley(at)2ndquadrant(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
Subject: | Re: POC: converting Lists into arrays |
Date: | 2019-03-04 19:03:27 |
Message-ID: | 20190304190327.n2g53f4ap7l4zusq@alap3.anarazel.de |
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Lists: | pgsql-hackers |
Hi,
On 2019-03-03 13:29:04 -0500, Tom Lane wrote:
> The cases I've been looking at suggest to me that we'd make far
> more progress on the excessive-palloc'ing front if we could redesign
> things to reduce unnecessary copying of parsetrees. Right now the
> planner does an awful lot of copying because of fear of unwanted
> modifications of multiply-linked subtrees. I suspect that we could
> reduce that overhead with some consistently enforced rules about
> not scribbling on input data structures; but it'd take a lot of work
> to get there, and I'm afraid it'd be easily broken :-(
Given the difficulty of this tasks, isn't your patch actually a *good*
attack on the problem? It makes copying lists considerably cheaper. As
you say, a more principled answer to this problem is hard, so attacking
it from the "make the constant factors smaller" side doesn't seem crazy?
Greetings,
Andres Freund
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