From: | Josh Berkus <josh(at)agliodbs(dot)com> |
---|---|
To: | pgsql-hackers(at)postgresql(dot)org |
Cc: | "Anjan Kumar(dot) A(dot)" <anjankumar(at)cse(dot)iitb(dot)ac(dot)in>, pgsql-chat(at)postgresql(dot)org, pgsql-benchmarks(at)postgresql(dot)org, pgsql-docs(at)postgresql(dot)org |
Subject: | Re: [HACKERS] Please Help: PostgreSQL Query Optimizer |
Date: | 2005-12-13 06:47:21 |
Message-ID: | 200512122247.21560.josh@agliodbs.com |
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Lists: | pgsql-benchmarks pgsql-chat pgsql-docs pgsql-hackers |
Anjan,
> But, in PostgreSQL all costs are scaled relative to a page fetch. If we
> make both sequential_page_fetch_cost and random_page_cost to "1", then we
> need to increase the various cpu_* paramters by multiplying the default
> values with appropriate Scaling Factor. Now, we need to determine this
> Scaling Factor.
I see, so you're saying that because the real cost of a page fetch has
decreased, the CPU_* costs should increase proportionally because relative to
the real costs of a page fetch they should be higher? That makes a sort of
sense.
The problem that you're going to run into is that currently we have no
particularly reason to believe that the various cpu_* costs are more than
very approximately correct as rules of thumb. So I think you'd be a lot
better off trying to come up with some means of computing the real cpu costs
of each operation, rather than trying to calculate a multiple of numbers
which may be wrong in the first place.
I know that someone on this list was working on a tool to digest EXPLAIN
ANALYZE results and run statistics on them. Can't remember who, though.
Also, I'm still curious on how you're handling shared_mem, work_mem and
maintenance_mem. You didn't answer last time.
--
Josh Berkus
Aglio Database Solutions
San Francisco
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