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From: Dmitry Dolgov <9erthalion6@gmail.com>
To: Floris Van Nee <florisvannee@Optiver.com>
Cc: Peter Geoghegan <pg@bowt.ie>
Cc: Jesper Pedersen <jesper.pedersen@redhat.com>
Cc: David Rowley <david.rowley@2ndquadrant.com>
Cc: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Cc: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Cc: Alvaro Herrera <alvherre@2ndquadrant.com>
Cc: Thomas Munro <thomas.munro@gmail.com>
Cc: James Coleman <jtc331@gmail.com>
Cc: Rafia Sabih <rafia.pghackers@gmail.com>
Cc: Jeff Janes <jeff.janes@gmail.com>
Cc: Bhushan Uparkar <bhushan.uparkar@gmail.com>
Cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
Cc: Alexander Korotkov <a.korotkov@postgrespro.ru>
Subject: Re: Index Skip Scan
Date: Wed, 22 Jan 2020 22:37:16 +0100
Message-ID: <20200122213716.ghvobtxsrfncjyye@localhost> (raw)
In-Reply-To: <105fd98b36dc4c0cb6b3dc41106b5556@opammb0562.comp.optiver.com>
References: <1e59d800b38141c5af2ad3a64cf9758e@opammb0562.comp.optiver.com>
	<802e46fa-dc2c-4c32-e55b-884e04aa7f12@redhat.com>
	<CAH2-Wzk6hvXvZ+1q4JBRunZkxmJwdXxnNsWuKJBp+F+mJuZYZw@mail.gmail.com>
	<20200121160942.eu4bvbu46nt223ug@localhost>
	<a713fef85da14e1fbca51d19c872d023@opammb0562.comp.optiver.com>
	<CAH2-WzmMEOtW_yXE6SJhbUWwLgBGr699NrkpGpMp8toW_ZgGrg@mail.gmail.com>
	<CAH2-Wzm0kLCdnM7rh8MC225E6befVYFTdHGv7-LgKXk32mTXsg@mail.gmail.com>
	<105fd98b36dc4c0cb6b3dc41106b5556@opammb0562.comp.optiver.com>

> On Wed, Jan 22, 2020 at 09:08:59PM +0000, Floris Van Nee wrote:
> > Note in particular that index scans cannot return the same index tuple twice -
> > - processing a page at a time ensures that that cannot happen.
> >
> > Can a loose index scan return the same tuple (i.e. a tuple with the same heap
> > TID) to the executor more than once?
> >
>
> The loose index scan shouldn't return a tuple twice. It should only be able to skip 'further', so that shouldn't be a problem.

Yes, it shouldn't happen.





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  To: pgsql-hackers@postgresql.org
  Cc: 9erthalion6@gmail.com, florisvannee@Optiver.com, pg@bowt.ie, jesper.pedersen@redhat.com, david.rowley@2ndquadrant.com, tomas.vondra@2ndquadrant.com, horikyota.ntt@gmail.com, alvherre@2ndquadrant.com, thomas.munro@gmail.com, jtc331@gmail.com, rafia.pghackers@gmail.com, jeff.janes@gmail.com, bhushan.uparkar@gmail.com, a.korotkov@postgrespro.ru
  Subject: Re: Index Skip Scan
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