Re: [HACKERS] Patch: Write Amplification Reduction Method (WARM)

On Thu, Mar 9, 2017 at 8:43 AM, Robert Haas <robertmhaas@gmail.com> wrote:
> On Wed, Mar 8, 2017 at 2:30 PM, Alvaro Herrera <alvherre@2ndquadrant.com> wrote:
>> Not really -- it's a bit slower actually in a synthetic case measuring
>> exactly the slowed-down case.  See
>> https://www.postgresql.org/message-id/CAD__OugK12ZqMWWjZiM-YyuD1y8JmMy6x9YEctNiF3rPp6hy0g@mail.gmail.com
>> I bet in normal cases it's unnoticeable.  If WARM flies, then it's going
>> to provide a larger improvement than is lost to this.
>
> Hmm, that test case isn't all that synthetic.  It's just a single
> column bulk update, which isn't anything all that crazy, and 5-10%
> isn't nothing.
>
> I'm kinda surprised it made that much difference, though.
>

I think it is because heap_getattr() is not that cheap.  We have
noticed the similar problem during development of scan key push down
work [1].

[1] - https://commitfest.postgresql.org/12/850/

-- 
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com