| From: | Stephan Szabo <sszabo(at)megazone(dot)bigpanda(dot)com> |
|---|---|
| To: | "Vig, Sandor (G/FI-2)" <Sandor(dot)Vig(at)audi(dot)hu> |
| Cc: | pgsql-performance(at)postgresql(dot)org |
| Subject: | Re: IS NULL vs IS NOT NULL |
| Date: | 2005-02-25 14:56:10 |
| Message-ID: | 20050225065133.B92053@megazone.bigpanda.com |
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| Thread: | |
| Lists: | pgsql-performance |
On Fri, 25 Feb 2005, Vig, Sandor (G/FI-2) wrote:
> Hi,
>
> Another "funny" thing: I have a query which runs
> on (Linux) PostgreSQL 7.4.x under 10 sec. I tried
> to run it on (Windows) PostgreSQL 8.0 yesterday.
> It didn't finished at all! (I shoot it down after 10 minutes)
> I made various tests and I figured out something interesting:
> The same query with:
> A, "history.undo_action_id > 0" runs in 10 sec.
> B, "history.undo_action_id is not null" runs in 10 sec.
> C, "history.undo_action_id is null" runs forever (?!)
> I used EXPLAIN but I couldn't figure out what the problem was.
EXPLAIN ANALYZE would be more useful. My first guess would be that the IS
NULL is returning many more than the estimated 1 row and as such a nested
loop is a bad plan. How many history rows match type_id=6 and
undo_action_id is null?
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