| From: | Joe Conway <mail(at)joeconway(dot)com> |
|---|---|
| To: | Hilmar Lapp <hlapp(at)gmx(dot)net> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-performance(at)postgresql(dot)org |
| Subject: | Re: join over 12 tables takes 3 secs to plan |
| Date: | 2003-01-02 21:40:23 |
| Message-ID: | 3E14B1C7.9040007@joeconway.com |
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| Lists: | pgsql-jdbc pgsql-performance |
Hilmar Lapp wrote:
> As an added note, appreciating that query optimization is a difficult
> problem, and I do think PostgreSQL is a great product. Having said
> that, I've written 16-table joins for Oracle and always found them to
> plan within a second or two, so that's why I thought there's nothing
> special about the query I posted ... I'm not saying this to be bashful
> about PostgreSQL, but rather to suggest that apparently there are ways
> to do it pretty fast.
I could be wrong, but I believe Oracle uses its rule based optimizer by
default, not its cost based optimizer. A rule based optimizer will be very
quick all the time, but might not pick the best plan all the time, because it
doesn't consider the statistics of the data. Any idea which one you were using
in your Oracle experience?
Joe
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