Horton

Re: postgres_fdw: using TABLESAMPLE to collect remote sample

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Tomas Vondra <tomas.vondra@enterprisedb.com>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2022-02-11T17:39:43Z
Lists: pgsql-hackers 
Tomas Vondra <tomas.vondra@enterprisedb.com> writes:
> So here we go. The patch does a very simple thing - it uses TABLESAMPLE 
> to collect/transfer just a small sample from the remote node, saving 
> both CPU and network.

This is great if the remote end has TABLESAMPLE, but pre-9.5 servers
don't, and postgres_fdw is supposed to still work with old servers.
So you need some conditionality for that.

			regards, tom lane

Commits

  1. Check relkind before using TABLESAMPLE in postgres_fdw

  2. Fix stale comment about sample_frac adjustment