On 07/30/2016 04:47 PM, Tom Lane wrote:
Pavel Stehule <pavel.steh...@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".
Agreed - breaking internal features for temporary tables is not
acceptable. I was thinking more about external code messing with
catalogs, but on second thought we probably need to keep the records in
pg_class anyway.
>
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.
Yeah, and I think the patch tries to do that, although in a rather
invasive / unprincipled way. But this will only work for the current
behavior (i.e. mostly what SQL standard means by LOCAL). For GLOBAL
temporary tables I think we need to keep physical catalog row, and only
override the storage filename.
regards
--
Tomas Vondra http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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