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Thread: how explain works

how explain works

From
Radhya sahal
Date:
Dear ,all
plz could any one help me !!!
how explian works as math equations to estimate cost with  constatn query parameters
such as cpu_tuple cost ,random page cost ...etc
 i want maths  expression  in order to know how these parameters will effect in cost ???
please any one can help me ??
 
 
Regards
Radhya...

Re: how explain works

From
Nathan Boley
Date:
> how explian works as math equations to estimate cost with  constatn query
> parameters
> such as cpu_tuple cost ,random page cost ...etc
>  i want maths  expression  in order to know how these parameters will effect
> in cost ???

The expressions are complicated, and they are certainly not linear as
you seem to think from your previous post.

> please any one can help me ??

What do you need this for? If your goal is to optimize a real
application, then you should just vary the cost parameters and measure
the resulting change in query times. If your interests are academic,
there were some excellent suggestions for places to start in response
to your previous post.

Best,
Nathan

Re: how explain works to Mr Nathan Boley

From
Radhya sahal
Date:
Thanks Mr Nathan Boley ,
i want these equations to solve thsese equtions of parameters and total time  in order to get each paramter formula
i need these formula  in my experiments is very important to know the rate for each parameter in total cost for plan. 
Best
Radhya..
From: Nathan Boley <npboley@gmail.com>
To: Radhya sahal <rad_cs_2006@yahoo.com>
Cc: pgsql-performance group <pgsql-performance@postgresql.org>
Sent: Mon, April 11, 2011 4:09:07 PM
Subject: Re: [PERFORM] how explain works

> how explian works as math equations to estimate cost with  constatn query
> parameters
> such as cpu_tuple cost ,random page cost ...etc
>  i want maths  expression  in order to know how these parameters will effect
> in cost ???

The expressions are complicated, and they are certainly not linear as
you seem to think from your previous post.

> please any one can help me ??

What do you need this for? If your goal is to optimize a real
application, then you should just vary the cost parameters and measure
the resulting change in query times. If your interests are academic,
there were some excellent suggestions for places to start in response
to your previous post.

Best,
Nathan

Re: how explain works to Mr Nathan Boley

From
Tomas Vondra
Date:
Dne 12.4.2011 01:22, Radhya sahal napsal(a):
> Thanks Mr Nathan Boley ,
> i want these equations to solve thsese equtions of parameters and total
> time  in order to get each paramter formula
> i need these formula  in my experiments is very important to know the
> rate for each parameter in total cost for plan.
> Best
> Radhya..

I don't think those equations are fully documented outside the source
code. If you really need the exact formulas, you'll have to dig into the
source codes and search there.

regards
Tomas