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From: Bruce Momjian <bruce@momjian.us>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Pavan Deolasee <pavan.deolasee@gmail.com>
Cc: Amit Kapila <amit.kapila16@gmail.com>
Cc: Alvaro Herrera <alvherre@2ndquadrant.com>
Cc: Jaime Casanova <jaime.casanova@2ndquadrant.com>
Cc: Haribabu Kommi <kommi.haribabu@gmail.com>
Cc: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: Patch: Write Amplification Reduction Method (WARM)
Date: Mon, 27 Mar 2017 22:19:28 -0400
Message-ID: <20170328021928.GA20361@momjian.us> (raw)
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On Mon, Mar 27, 2017 at 04:29:56PM -0400, Robert Haas wrote:
> On Thu, Mar 23, 2017 at 2:47 PM, Pavan Deolasee
> <pavan.deolasee@gmail.com> wrote:
> > It's quite hard to say that until we see many more benchmarks. As author of
> > the patch, I might have got repetitive with my benchmarks. But I've seen
> > over 50% improvement in TPS even without chain conversion (6 indexes on a 12
> > column table test).
> 
> This seems quite mystifying.  What can account for such a large
> performance difference in such a pessimal scenario?  It seems to me
> that without chain conversion, WARM can only apply to each row once
> and therefore no sustained performance improvement should be possible
> -- unless rows are regularly being moved to new blocks, in which case
> those updates would "reset" the ability to again perform an update.
> However, one would hope that most updates get done within a single
> block, so that the row-moves-to-new-block case wouldn't happen very
> often.
> 
> I'm perplexed.

Yes, I asked the same question in this email:

	https://www.postgresql.org/message-id/20170321190000.GE16918@momjian.us

-- 
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

+ As you are, so once was I.  As I am, so you will be. +
+                      Ancient Roman grave inscription +


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