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

On Thu, Feb 23, 2017 at 03:45:24PM -0300, Alvaro Herrera wrote:
> 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.

Right.

> > and potentially trim the first HOT chain as those tuples become
> > invisible.
> 
> That can already happen even without WARM, no?

Uh, the point is that with WARM those four early tuples can be removed
via a prune, rather than requiring a VACUUM. Without WARM, the fourth
tuple can't be removed until the index is cleared by VACUUM.

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

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