From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | "Marinos J(dot) Yannikos" <mjy(at)geizhals(dot)at> |
Cc: | pgsql-performance(at)postgresql(dot)org |
Subject: | Re: why do optimizer parameters have to be set manually? |
Date: | 2003-12-18 19:56:20 |
Message-ID: | 22686.1071777380@sss.pgh.pa.us |
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Lists: | pgsql-performance |
"Marinos J. Yannikos" <mjy(at)geizhals(dot)at> writes:
> it seems to me that the optimizer parameters (like random_page_cost
> etc.) could easily be calculated and adjusted dynamically be the DB
> backend based on the planner's cost estimates and actual run times for
> different queries. Perhaps the developers could comment on that?
No, they are not that easy to determine. In particular I think the idea
of automatically feeding back error measurements is hopeless, because
you cannot tell which parameters are wrong.
> I'm not sure how the parameters are used internally (apart from whatever
> "EXPLAIN" shows), but if cpu_operator_cost is the same for all
> operators, this should probably also be adjusted for individual
> operators (I suppose that ">" is not as costly as "~*").
In theory perhaps, but in practice this is far down in the noise in most
situations.
regards, tom lane
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