Date: Thu, 23 Feb 2017 15:45:24 -0300
From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Bruce Momjian <bruce@momjian.us>
Cc: Pavan Deolasee <pavan.deolasee@gmail.com>,
	Jaime Casanova <jaime.casanova@2ndquadrant.com>,
	Haribabu Kommi <kommi.haribabu@gmail.com>,
	Tomas Vondra <tomas.vondra@2ndquadrant.com>,
	pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: Patch: Write Amplification Reduction Method (WARM)
Message-ID: <20170223184524.icdwoh34txoob2ja@alvherre.pgsql>
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Bruce Momjian wrote:

> Well, let's walk through this.  Let's suppose you have three updates
> that stay on the same page and don't update any indexed columns --- that
> would produce a HOT chain of four tuples.  If you then do an update that
> changes an indexed column, prior to this patch, you get a normal update,
> and more HOT updates can be added to this.  With WARM, we can join those
> chains

With WARM, what happens is that the first three updates are HOT updates
just like currently, and the fourth one is a WARM update.

> and potentially trim the first HOT chain as those tuples become
> invisible.

That can already happen even without WARM, no?

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services


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