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From: Mihail Nikalayeu <mihailnikalayeu@gmail.com>
Date: Mon, 16 Jun 2025 22:00:59 +0200
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Subject: Re: Revisiting {CREATE INDEX, REINDEX} CONCURRENTLY improvements
To: Sergey Sargsyan <sergey.sargsyan.2001@gmail.com>
Cc: =?UTF-8?Q?=C3=81lvaro_Herrera?= <alvherre@kurilemu.de>,
	Andres Freund <andres@anarazel.de>, Michael Paquier <michael@paquier.xyz>,
	PostgreSQL Hackers <pgsql-hackers@postgresql.org>,
 Andrey Borodin <amborodin86@gmail.com>,
	Melanie Plageman <melanieplageman@gmail.com>,
	Matthias van de Meent <boekewurm+postgres@gmail.com>
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Hello, Sergey!

> I think it's to avoid duplicate errors when adding tuples from STIP to th=
e main index,
> but couldn't we just suppress that error during validation and skip the n=
ew tuple insertion if it already exists?

In some cases, it is not possible:
=E2=80=93 Some index types (GiST, GIN, BRIN) do not provide an easy way to
detect such duplicates.
=E2=80=93 When we are building a unique index, we cannot simply skip
duplicates, because doing so would also skip the rows that should
prevent the unique index from being created (unless we add extra logic
for B-tree indexes to compare TIDs as well).

> The main index may get huge after building, and iterating over it in a si=
ngle thread and then sorting tids can be time consuming.
My tests indicate that the overhead is minor compared with the time
spent scanning the heap and building the index itself.

> At least I guess one can skip it when STIP is empty.
Yes, that=E2=80=99s a good idea; I=E2=80=99ll add it later.

> p.s. I noticed that `stip.c` has a lot of functions that don't follow the=
 Postgres coding style of return type on separate line.
Hmm... I=E2=80=99ll fix that as well.

Best regards,
Mikhail.