| From: | Craig Ringer <craig(at)2ndquadrant(dot)com> |
|---|---|
| To: | Peter Geoghegan <pg(at)heroku(dot)com> |
| Cc: | pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Vacuum, Freeze and Analyze: the big picture |
| Date: | 2013-06-03 23:45:19 |
| Message-ID: | 51AD2A8F.6080302@2ndquadrant.com |
| Views: | Raw Message | Whole Thread | Download mbox | Resend email |
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| Lists: | pgsql-hackers |
On 06/04/2013 05:27 AM, Peter Geoghegan wrote:
> On Mon, Jun 3, 2013 at 5:03 AM, Craig Ringer <craig(at)2ndquadrant(dot)com> wrote:
>> I've seen cases on Stack Overflow and elsewhere in which disk merge
>> sorts perform vastly better than in-memory quicksort, so the user
>> benefited from greatly *lowering* work_mem.
> I've heard of that happening on Oracle, when the external sort is
> capable of taking advantage of I/O parallelism, but I have a pretty
> hard time believing that it could happen with Postgres under any
> circumstances.
IIRC it's usually occurred with very expensive comparison operations.
I'll see if I can find one of the SO cases.
--
Craig Ringer http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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