Horton

Re: Reduce "Var IS [NOT] NULL" quals during constant folding

Richard Guo <guofenglinux@gmail.com>

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From: Richard Guo <guofenglinux@gmail.com>
To: Andrei Lepikhov <lepihov@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Robert Haas <robertmhaas@gmail.com>, Peter Eisentraut <peter@eisentraut.org>, David Rowley <dgrowleyml@gmail.com>, Tender Wang <tndrwang@gmail.com>, Pg Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2025-07-02T09:14:48Z
Lists: pgsql-hackers

Commits

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  1. Fix misuse of Relids for storing attribute numbers

  2. Reduce "Var IS [NOT] NULL" quals during constant folding

  3. Centralize collection of catalog info needed early in the planner

  4. Expand virtual generated columns before sublink pull-up

  5. Expand virtual generated columns in the planner

On Wed, Jul 2, 2025 at 4:32 PM Andrei Lepikhov <lepihov@gmail.com> wrote:
> I must say that I appreciate Tom's idea and see significant benefits in
> making the parse tree a read-only structure. In complex queries, it can
> be frustrating to make copies of the parse tree, leading to complaints
> from users about insufficient memory allocation. This is why, in our
> enterprise fork, we support a specific option to avoid copying the parse
> tree multiple times.

I don't see how the changes in this patchset violate Tom's proposal
regarding keeping the parse tree read-only.  The only potential issue
I can see is that we may clear the rte->inh flag in some cases -- but
that behavior has existed for a long time, not starting from this
patchset.

> Therefore, it would be better to find a way to refactor the
> `preprocess_relation_rtes` function to gather table statistics lazily
> into the hash table when they are needed. For example, we could do this
> at the moment of creating the `RelOptInfo` or before a subquery pull-up,
> without modifying the RTE at all.

All the catalog information collected in preprocess_relation_rtes() is
needed very early in the planner.  I don't see how we could move that
logic to a later stage, such as at the moment of creating RelOptInfos
as you mentioned.

Thanks
Richard