| From: | Dmitry Dolgov <9erthalion6(at)gmail(dot)com> |
|---|---|
| To: | Dilip Kumar <dilipbalaut(at)gmail(dot)com> |
| Cc: | Floris Van Nee <florisvannee(at)optiver(dot)com>, David Rowley <dgrowleyml(at)gmail(dot)com>, Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com>, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, Peter Geoghegan <pg(at)bowt(dot)ie>, Jesper Pedersen <jesper(dot)pedersen(at)redhat(dot)com>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Thomas Munro <thomas(dot)munro(at)gmail(dot)com>, James Coleman <jtc331(at)gmail(dot)com>, Rafia Sabih <rafia(dot)pghackers(at)gmail(dot)com>, Jeff Janes <jeff(dot)janes(at)gmail(dot)com>, "bhushan(dot)uparkar(at)gmail(dot)com" <bhushan(dot)uparkar(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, Alexander Korotkov <a(dot)korotkov(at)postgrespro(dot)ru> |
| Subject: | Re: Index Skip Scan |
| Date: | 2020-05-15 12:38:02 |
| Message-ID: | 20200515123802.xhppukhcqemmnbqe@localhost |
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| Lists: | pgsql-hackers |
> 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!
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