From: | Floris Van Nee <florisvannee(at)Optiver(dot)com> |
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To: | Dmitry Dolgov <9erthalion6(at)gmail(dot)com>, David Rowley <david(dot)rowley(at)2ndquadrant(dot)com>, Jesper Pedersen <jesper(dot)pedersen(at)redhat(dot)com> |
Cc: | 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>, Peter Geoghegan <pg(at)bowt(dot)ie>, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com>, Bhushan Uparkar <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: | 2019-07-10 14:52:21 |
Message-ID: | 1562770342222.94509@Optiver.com |
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Thread: | |
Lists: | pgsql-hackers |
> Thanks for testing! Could you provide a test case to show what exactly is the
> problem?
create table a (a int, b int, c int);
insert into a (select vs, ks, 10 from generate_series(1,5) vs, generate_series(1, 10000) ks);
create index on a (a,b);
analyze a;
set enable_indexskipscan=1; // setting this to 0 yields different results
set random_page_cost=1;
explain SELECT DISTINCT ON (a) a,b FROM a;
BEGIN;
DECLARE c SCROLL CURSOR FOR SELECT DISTINCT ON (a) a,b FROM a;
FETCH FROM c;
FETCH BACKWARD FROM c;
FETCH 6 FROM c;
FETCH BACKWARD 6 FROM c;
FETCH 6 FROM c;
FETCH BACKWARD 6 FROM c;
END;
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