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From: Ronan Dunklau <[email protected]>
To: Alexander Korotkov <[email protected]>
To: Tom Lane <[email protected]>
Cc: Michael Paquier <[email protected]>
Cc: [email protected]
Subject: Re: Fix gin index cost estimation
Date: Fri, 02 Dec 2022 11:19:11 +0100
Message-ID: <13151261.uLZWGnKmhe@aivenlaptop> (raw)
In-Reply-To: <[email protected]>
References: <3188617.44csPzL39Z@aivenronan>
	<CAPpHfdt45WZPcS-R1BYLgixv+vW_+dTom6GHa-XZPu4mtfXTRg@mail.gmail.com>
	<[email protected]>

Le mardi 25 octobre 2022, 16:18:57 CET Tom Lane a écrit :
> Alexander Korotkov <[email protected]> writes:
> > I think Tom's point was that it's wrong to add a separate entry-tree CPU
> > cost estimation to another estimation, which tries (very inadequately) to
> > estimate the whole scan cost. Instead, I propose writing better
> > estimations
> > for both entry-tree CPU cost and data-trees CPU cost and replacing
> > existing
> > CPU estimation altogether.
> 
> Great idea, if someone is willing to do it ...
> 
> 			regards, tom lane

Hello,

Sorry for the delay, but here is an updated patch which changes the costing in 
the following way:

- add a descent cost similar to the btree one is charged for the initial 
entry-tree
- additionally, a charge is applied per page in both the entry tree and 
posting trees / lists
- instead of charging the quals to each tuple, charge them per entry only. We 
still charge cpu_index_tuple_cost per tuple though.

With those changes, no need to tweak the magic number formula estimating the 
number of pages. Maybe we can come up with something better for estimating 
those later on ?

Best regards,

--
Ronan Dunklau

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