| From: | Thom Brown <thom(at)linux(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Bruce Momjian <bruce(at)momjian(dot)us>, pgsql-committers(at)postgresql(dot)org |
| Subject: | Re: pgsql: Consider index-only scans even when there is no matching qual or |
| Date: | 2011-10-11 20:56:07 |
| Message-ID: | CAA-aLv5zAZsuefLPf__8PFfD3peyB+f=AsuMEAoH8UnWpDuRqA@mail.gmail.com |
| Views: | Raw Message | Whole Thread | Download mbox | Resend email |
| Thread: | |
| Lists: | pgsql-committers |
On 11 October 2011 21:45, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Thom Brown <thom(at)linux(dot)com> writes:
>> So an index-only scan is 30 times slower in this particular test case.
>
> Don't see why you'd find that unexpected. If you have to visit all the
> rows, a seqscan is usually going to be the best way. An indexscan only
> has a chance of winning when the index is much smaller than the table,
> which isn't the case in your example, even if you hadn't seen to it that
> the index wasn't particularly nicely physically ordered.
Ah okay, understood.
--
Thom Brown
Twitter: @darkixion
IRC (freenode): dark_ixion
Registered Linux user: #516935
EnterpriseDB UK: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
| From | Date | Subject | |
|---|---|---|---|
| Next Message | Bruce Momjian | 2011-10-11 21:33:54 | pgsql: Document that not backing up postmaster.pid and postmaster.opts |
| Previous Message | Tom Lane | 2011-10-11 20:45:38 | Re: pgsql: Consider index-only scans even when there is no matching qual or |