Date: Fri, 15 May 2020 14:38:02 +0200
From: Dmitry Dolgov <9erthalion6@gmail.com>
To: Dilip Kumar <dilipbalaut@gmail.com>
Cc: Floris Van Nee <florisvannee@optiver.com>,
	David Rowley <dgrowleyml@gmail.com>,
	Kyotaro Horiguchi <horikyota.ntt@gmail.com>,
	Tomas Vondra <tomas.vondra@2ndquadrant.com>,
	Peter Geoghegan <pg@bowt.ie>,
	Jesper Pedersen <jesper.pedersen@redhat.com>,
	Alvaro Herrera <alvherre@2ndquadrant.com>,
	Thomas Munro <thomas.munro@gmail.com>,
	James Coleman <jtc331@gmail.com>,
	Rafia Sabih <rafia.pghackers@gmail.com>,
	Jeff Janes <jeff.janes@gmail.com>,
	"bhushan.uparkar@gmail.com" <bhushan.uparkar@gmail.com>,
	PostgreSQL-development <pgsql-hackers@postgresql.org>,
	Alexander Korotkov <a.korotkov@postgrespro.ru>
Subject: Re: Index Skip Scan
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> On Wed, May 13, 2020 at 02:37:21PM +0530, Dilip Kumar wrote:
>
> + if (_bt_scankey_within_page(scan, so->skipScanKey, so->currPos.buf, dir))
> + {
>
> Here we expect whether the "next" unique key can be found on this page
> or not, but we are using the function which suggested whether the
> "current" key can be found on this page or not.  I think in boundary
> cases where the high key is equal to the current key, this function
> will return true (which is expected from this function), and based on
> that we will simply scan the current page and IMHO that cost could be
> avoided no?

Yes, looks like you're right, there is indeed an unecessary extra scan
happening. To avoid that we can see the key->nextkey and adjust higher
boundary correspondingly. Will also add this into the next rebased
patch, thanks!