| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | decibel <decibel(at)decibel(dot)org>, Greg Smith <gsmith(at)gregsmith(dot)com>, jd(at)commandprompt(dot)com, Grzegorz Jaskiewicz <gj(at)pointblue(dot)com(dot)pl>, Bernd Helmle <mailings(at)oopsware(dot)de>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: The science of optimization in practical terms? |
| Date: | 2009-02-18 06:34:25 |
| Message-ID: | 807.1234938865@sss.pgh.pa.us |
| Views: | Raw Message | Whole Thread | Download mbox | Resend email |
| Thread: | |
| Lists: | pgsql-hackers |
Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> I'm interested to know whether anyone else shares my belief that
> nested loops are the cause of most really bad plans. What usually
> happens to me is that the planner develops some unwarranted optimism
> about the number of rows likely to be generated by the outer side of
> the join and decides that it's not worth sorting the inner side or
> building a hash table or using an index, and that the right thing to
> do is just rescan the inner node on every pass. When the outer side
> returns three or four orders of magnitude more results than expected,
> ka-pow!
And then there is the other half of the world, who complain because it
*didn't* pick a nestloop for some query that would have run in much less
time if it had.
regards, tom lane
| From | Date | Subject | |
|---|---|---|---|
| Next Message | Kris Jurka | 2009-02-18 07:34:48 | Re: [Pljava-dev] Re: Should creating a new base type require superuser status? |
| Previous Message | Thomas Hallgren | 2009-02-18 06:07:11 | Re: [Pljava-dev] Re: Should creating a new base type require superuser status? |