Re: Removing unneeded self joins

Hi!

I think this is a neat optimization.

On Tue, Sep 12, 2023 at 4:58 PM Andrey Lepikhov
<a(dot)lepikhov(at)postgrespro(dot)ru> wrote:
> On 5/7/2023 21:28, Andrey Lepikhov wrote:
> > During the significant code revision in v.41 I lost some replacement
> > operations. Here is the fix and extra tests to check this in the future.
> > Also, Tom added the JoinDomain structure five months ago, and I added
> > code to replace relids for that place too.
> > One more thing, I found out that we didn't replace SJs, defined by
> > baserestrictinfos if no one self-join clause have existed for the join.
> > Now, it is fixed, and the test has been added.
> > To understand changes readily, see the delta file in the attachment.
> Here is new patch in attachment. Rebased on current master and some
> minor gaffes are fixed.

I went through the thread and I think the patch gets better shape. A
couple of notes from my side.
1) Why replace_relid() makes a copy of lids only on insert/replace of
a member, but performs deletion in-place?
2) It would be nice to skip the insertion of IS NOT NULL checks when
they are not necessary. [1] points that infrastructure from [2] might
be useful. The patchset from [2] seems committed mow. However, I
can't see it is directly helpful in this matter. Could we just skip
adding IS NOT NULL clause for the columns, that have
pg_attribute.attnotnull set?

Links
1. https://www.postgresql.org/message-id/2375492.jE0xQCEvom%40aivenronan
2. https://www.postgresql.org/message-id/flat/830269.1656693747%40sss.pgh.pa.us

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Regards,
Alexander Korotkov