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Re: testing HS/SR - 1 vs 2 performance

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Simon Riggs <simon(at)2ndquadrant(dot)com>, Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, Erik Rijkers <er(at)xs4all(dot)nl>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: testing HS/SR - 1 vs 2 performance
Date: 2010-04-17 15:25:46
Message-ID: y2u603c8f071004170825zc8ae5f0fv19f999fe72e6f666@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Sat, Apr 17, 2010 at 11:13 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Simon Riggs <simon(at)2ndQuadrant(dot)com> writes:
>> AFAICS the example you give isn't correct.
>
>> We would lay out the values like this
>
>> W-3 W-2 W-1 W 3 4 5
>
>> where W is the wrap value
>
> Stop right there, you're already failing to think clearly.  There is no
> unique "wrap value", all values act the same in circular XID space.

Or to put it a different way, what happens when the "wrap value"
changes?  An array that was in order under one wrap value can cease to
be in order under another.

...Robert

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