| From: | Michael Glaesemann <grzm(at)seespotcode(dot)net> |
|---|---|
| To: | Heikki Linnakangas <heikki(at)enterprisedb(dot)com> |
| Cc: | Alvaro Herrera <alvherre(at)commandprompt(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Patches <pgsql-patches(at)postgresql(dot)org>, Jeff Davis <pgsql(at)j-davis(dot)com> |
| Subject: | Re: Synchronized scans |
| Date: | 2007-06-04 21:28:06 |
| Message-ID: | B5C8AC7A-3722-4297-A4F7-98D07054B9C2@seespotcode.net |
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| Lists: | pgsql-patches |
On Jun 4, 2007, at 15:24 , Heikki Linnakangas wrote:
> I don't think anyone can reasonably expect to get the same ordering
> when the same query issued twice in general, but within the same
> transaction it wouldn't be that unreasonable.
The order rows are returned without an ORDER BY clause *is*
implementation dependent, and is not guaranteed, at least by the
spec. Granted, LIMIT without ORDER BY (and DISTINCT for that matter)
brings this into sharp relief.
> I think the warning on LIMIT without ORDER BY is a good idea,
> regardless of the synchronized scans patch.
I'm not saying this isn't a good idea, but are there other places
where there might be gotchas for the unwary, such as DISTINCT without
ORDER BY or (for an unrelated example) UNION versus UNION ALL? How
many of these types of messages would be useful?
Michael Glaesemann
grzm seespotcode net
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