| From: | Jeff Janes <jeff(dot)janes(at)gmail(dot)com> |
|---|---|
| To: | Ants Aasma <ants(at)cybertec(dot)at> |
| Cc: | Yan Chunlu <springrider(at)gmail(dot)com>, Craig Ringer <ringerc(at)ringerc(dot)id(dot)au>, Albe Laurenz <laurenz(dot)albe(at)wien(dot)gv(dot)at>, "pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org> |
| Subject: | Re: how could select id=xx so slow? |
| Date: | 2012-07-12 18:53:35 |
| Message-ID: | CAMkU=1xb-5uqpc=fG42vmWUo9RrxDKE5pnwpNHBY=4rs8XE39g@mail.gmail.com |
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| Lists: | pgsql-performance |
On Thu, Jul 12, 2012 at 9:07 AM, Ants Aasma <ants(at)cybertec(dot)at> wrote:
> On Thu, Jul 12, 2012 at 3:48 PM, Yan Chunlu <springrider(at)gmail(dot)com> wrote:
>> yes the system seems overloaded, I am dealing with a simple "INSERT" but not
>> sure if it is normal that it took more time than the explain estimated:
>
> The estimated cost is in arbitrary units, its purpose is to compare
> different execution plans, not estimate time taken. So it's completely
> normal that it doesn't match actual time taken.
Right. And to make explicit what you implied, when there is only one
to do something (like insert a row, or do maintenance on an index) it
often doesn't even attempt to cost that at all as there is no choice.
So it is not just a matter of units.
Cheers,
Jeff
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