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

On Tue, Mar 21, 2017 at 11:45:09PM +0530, Pavan Deolasee wrote:
>     Early in the discussion we talked about allowing multiple changes per
>     WARM chain if they all changed the same index and were in the same
>     direction so there were no duplicates, but it was complicated.  There
>     was also discussion about checking the index during INSERT/UPDATE to see
>     if there was a duplicate.  However, those ideas never led to further
>     discussion.
> 
> 
> Well, once I started thinking about how to do vacuum etc, I realised that any
> mechanism which allows unlimited (even handful) updates per chain is going to
> be very complex and error prone. But if someone has ideas to do that, I am
> open. I must say though, it will make an already complex problem even more
> complex.

Yes, that is where we got stuck.  Have enough people studied the issue
to know that there are no simple answers?

>     I know the current patch yields good results, but only on a narrow test
>     case,
> 
> 
> Hmm. I am kinda surprised you say that because I never thought it was a narrow
> test case that we are targeting here. But may be I'm wrong.

Well, it is really a question of how often you want to do a second WARM
update (not possible) vs. the frequency of lazy vacuum.  I assumed that
would be a 100X or 10kX difference, but I am not sure myself either.  My
initial guess was that only allowing a single WARM update between lazy
vacuums would show no improvementin in real-world workloads, but maybe I
am wrong.

--  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. +
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