Horton

Re: Should we optimize the `ORDER BY random() LIMIT x` case?

Nico Williams <nico@cryptonector.com>

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From: Nico Williams <nico@cryptonector.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Aleksander Alekseev <aleksander@timescale.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Andrei Lepikhov <lepihov@gmail.com>, wenhui qiu <qiuwenhuifx@gmail.com>
Date: 2025-05-16T21:50:49Z
Lists: pgsql-hackers 
On Fri, May 16, 2025 at 09:01:50AM -0400, Tom Lane wrote:
> Seems to me the obvious answer is to extend TABLESAMPLE (or at least, some
> of the tablesample methods) to allow it to work on a subquery.

The key here is that we need one bit of state between rows: the count of
rows seen so far.