Re: Patch: Write Amplification Reduction Method (WARM)

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(dot)deolasee(at)gmail(dot)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

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Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

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