Date: Thu, 30 Mar 2017 13:47:45 -0400
From: Bruce Momjian <bruce@momjian.us>
To: Alvaro Herrera <alvherre@2ndquadrant.com>
Cc: Pavan Deolasee <pavan.deolasee@gmail.com>,
	Robert Haas <robertmhaas@gmail.com>,
	Amit Kapila <amit.kapila16@gmail.com>,
	Jaime Casanova <jaime.casanova@2ndquadrant.com>,
	Haribabu Kommi <kommi.haribabu@gmail.com>,
	Tomas Vondra <tomas.vondra@2ndquadrant.com>,
	pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: Patch: Write Amplification Reduction Method (WARM)
Message-ID: <20170330174745.GA6593@momjian.us>
References: <20170321194811.GG16918@momjian.us>
 <20170321195616.uhxtpwbbl6xlhuok@alvherre.pgsql>
 <20170321200458.GA2827@momjian.us>
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On Tue, Mar 21, 2017 at 04:04:58PM -0400, Bruce Momjian wrote:
> On Tue, Mar 21, 2017 at 04:56:16PM -0300, Alvaro Herrera wrote:
> > Bruce Momjian wrote:
> > > On Tue, Mar 21, 2017 at 04:43:58PM -0300, Alvaro Herrera wrote:
> > > > Bruce Momjian wrote:
> > > > 
> > > > > I don't think it makes sense to try and save bits and add complexity
> > > > > when we have no idea if we will ever use them,
> > > > 
> > > > If we find ourselves in dire need of additional bits, there is a known
> > > > mechanism to get back 2 bits from old-style VACUUM FULL.  I assume that
> > > > the reason nobody has bothered to write the code for that is that
> > > > there's no *that* much interest.
> > > 
> > > We have no way of tracking if users still have pages that used the bits
> > > via pg_upgrade before they were removed.
> > 
> > Yes, that's exactly the code that needs to be written.
> 
> Yes, but once it is written it will take years before those bits can be
> used on most installations.

Actually, the 2 bits from old-style VACUUM FULL bits could be reused if
one of the WARM bits would be set  when it is checked.  The WARM bits
will all be zero on pre-9.0.  The check would have to be checking the
old-style VACUUM FULL bit and checking that a WARM bit is set.

-- 
  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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