Re: again on index usage

Daniel Kalchev wrote:
> >>>Tom Lane said:
>  > "Zeugswetter Andreas SB SD" <ZeugswetterA@spardat.at> writes:
>  > > My preference would actually be a way to make the optimizer
>  > > choose a plan that causes minimal workload, and not shortest runtime 
>  > 
>  > ?? I am not sure that I see the difference.
> 
> There can be difference only if the optimizer takes into account already 
> executing plans (by other backends).
> 
>  > What I think you are saying is that when there's lots of competing work,
>  > seqscans have less advantage over indexscans because the
>  > sequential-access locality advantage is lost when the disk drive has to
>  > go off and service some other request.
> 
> This is exactly my point. The primary goal of the optimizer in my opinion 
> should be to avoid trashing. :-) Now, it is not easy to figure out when the 
> system starts trashing - at least not a portable way I can think of 
> immediately.

I have always felt some feedback mechanism from the executor back to the
optimizer was required but I was never sure quite how to implement it.

--  Bruce Momjian                        |  http://candle.pha.pa.us pgman@candle.pha.pa.us               |  (610)
853-3000+  If your life is a hard drive,     |  830 Blythe Avenue +  Christ can be your backup.        |  Drexel Hill,
Pennsylvania19026