Skip site navigation (1) Skip section navigation (2)

Re: cost_nonsequential_access()

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Manfred Koizar <mkoi-pg(at)aon(dot)at>
Cc: pgsql-patches(at)postgresql(dot)org
Subject: Re: cost_nonsequential_access()
Date: 2004-06-08 17:13:01
Message-ID: 3288.1086714781@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-patches
Manfred Koizar <mkoi-pg(at)aon(dot)at> writes:
> On Tue, 08 Jun 2004 11:13:43 -0400, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> This patch seems to do considerably more violence to the equations than
>> is needed to cover that oversight, though.  The old behavior was
>> intentionally nonlinear in relsize; this is not.

> The comment says "entirely ad-hoc" and I didn't see a particular reason
> why the lower half should be nonlinear in relsize while the upper half
> is linear in 1/relsize.

Incremental changes in the relsize fraction are not going to change the
cost much except near 1, so I was after a curve that went like this
(pardon the crude artwork):


rpc                                            ***********************
                                        *******
                                    ****
                                  **
cost                             *
                                *
                               *
                             **
                         ****
                 ********
1.0 *************
    0                           1                                large
                          relsize fraction

I don't think replacing the lower half of this with a straight line
segment is an improvement.

Possibly the relsize axis ought to be measured on a log scale, or
something like that, but that didn't seem to work nicely when relsize
approaches zero.

			regards, tom lane

In response to

Responses

pgsql-patches by date

Next:From: Manfred KoizarDate: 2004-06-08 18:18:31
Subject: Re: cost_nonsequential_access()
Previous:From: Fabien COELHODate: 2004-06-08 16:00:02
Subject: Re: fix schema ownership for database owner on first

Privacy Policy | About PostgreSQL
Copyright © 1996-2014 The PostgreSQL Global Development Group