From: Tom Lane <tgl@sss.pgh.pa.us>
To: Pavel Stehule <pavel.stehule@gmail.com>
Cc: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Cc: PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Cc: Aleksander Alekseev <a.alekseev@postgrespro.ru>
Subject: Re: [Patch] Temporary tables that do not bloat pg_catalog (a.k.a fast temp tables)
Date: Sat, 30 Jul 2016 10:47:10 -0400
Message-ID: <1184.1469890030@sss.pgh.pa.us> (raw)
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Pavel Stehule <pavel.stehule@gmail.com> writes:
> But there are some patterns used with work with temp tables,that should not
> working, and we would to decide if we prepare workaround or not.
> -- problematic pattern (old code)
> IF NOT EXISTS(SELECT * FROM pg_class WHERE ....) THEN
> CREATE TEMP TABLE xxx()
> ELSE
> TRUNCATE TABLE xxx;
> END IF;
> -- modern patter (new code)
> BEGIN
> TRUNCATE TABLE xxx;
> EXCEPTION WHEN ..... THEN
> CREATE TEMP TABLE(...)
> END;
If the former stops working, that's a sufficient reason to reject the
patch: it hasn't been thought through carefully enough. The key reason
why I don't think that's negotiable is that if there aren't (apparently)
catalog entries corresponding to the temp tables, that will almost
certainly break many things in the backend and third-party extensions,
not only user code patterns like this one. We'd constantly be fielding
bug reports that "feature X doesn't work with temp tables anymore".
In short, I think that the way to make something like this work is to
figure out how to have "virtual" catalog rows describing a temp table.
Or maybe to partition the catalogs so that vacuuming away temp-table
rows is easier/cheaper than today.
regards, tom lane
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To: pgsql-hackers@postgresql.org
Cc: tgl@sss.pgh.pa.us, pavel.stehule@gmail.com, tomas.vondra@2ndquadrant.com, a.alekseev@postgrespro.ru
Subject: Re: [Patch] Temporary tables that do not bloat pg_catalog (a.k.a fast temp tables)
In-Reply-To: <1184.1469890030@sss.pgh.pa.us>
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