Date: Mon, 20 Mar 2017 13:12:02 -0300
From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Pavan Deolasee <pavan.deolasee@gmail.com>
Cc: Robert Haas <robertmhaas@gmail.com>, Bruce Momjian <bruce@momjian.us>,
	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: <20170320161202.dytk3ski7f7yldj6@alvherre.pgsql>
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Pavan Deolasee wrote:
> On Tue, Mar 14, 2017 at 7:17 AM, Alvaro Herrera <alvherre@2ndquadrant.com>
> wrote:

> > I didn't like this comment very much.  But it's not necessary: you have
> > already given relcache responsibility for setting rd_supportswarm.  The
> > only problem seems to be that you set it in RelationGetIndexAttrBitmap
> > instead of RelationGetIndexList, but it's not clear to me why.  I think
> > if the latter function is in charge, then we can trust the flag more
> > than the current situation.
> 
> I looked at this today.  AFAICS we don't have access to rd_amroutine in
> RelationGetIndexList since we don't actually call index_open() in that
> function. Would it be safe to do that? I'll give it a shot, but thought of
> asking here first.

Ah, you're right, we only have the pg_index tuple for the index, not the
pg_am one.  I think one pg_am cache lookup isn't really all that
terrible (though we should ensure that there's no circularity problem in
doing that), but I doubt that going to the trouble of invoking the
amhandler just to figure out if it supports WARM is acceptable.

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services


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