Re: [PERFORM] index scan through a subquery
Tom Lane wrote: I need the lovely index scan, but my table is hidden behind a view, and all I get is the ugly sequential scan. Any ideas on how to convince the optimizer to unfold the subquery properly? You should provide some context in this sort of gripe, like which PG version you're using. But I'm going to guess that it's 8.2.x, because 8.1.x gets it right :-(. Try the attached. Good guess; I was indeed talking about the current release rather than the previous release. Also, apologies for the tone of my post: I was attempting to be jovial, but in retrospect, I see how it reads as a gripe, which I guess evoked your frowny-face emoticon. Thanks for the quick response, elegant fix, and ongoing excellent work! Cheers, Bill Index: planagg.c === RCS file: /cvsroot/pgsql/src/backend/optimizer/plan/planagg.c,v retrieving revision 1.25 diff -c -r1.25 planagg.c *** planagg.c 9 Jan 2007 02:14:13 - 1.25 --- planagg.c 6 Feb 2007 06:30:23 - *** *** 70,75 --- 70,76 optimize_minmax_aggregates(PlannerInfo *root, List *tlist, Path *best_path) { Query *parse = root-parse; + FromExpr *jtnode; RangeTblRef *rtr; RangeTblEntry *rte; RelOptInfo *rel; *** *** 102,115 * We also restrict the query to reference exactly one table, since join * conditions can't be handled reasonably. (We could perhaps handle a * query containing cartesian-product joins, but it hardly seems worth the ! * trouble.) */ ! Assert(parse-jointree != NULL IsA(parse-jointree, FromExpr)); ! if (list_length(parse-jointree-fromlist) != 1) ! return NULL; ! rtr = (RangeTblRef *) linitial(parse-jointree-fromlist); ! if (!IsA(rtr, RangeTblRef)) return NULL; rte = rt_fetch(rtr-rtindex, parse-rtable); if (rte-rtekind != RTE_RELATION || rte-inh) return NULL; --- 103,121 * We also restrict the query to reference exactly one table, since join * conditions can't be handled reasonably. (We could perhaps handle a * query containing cartesian-product joins, but it hardly seems worth the ! * trouble.) However, the single real table could be buried in several ! * levels of FromExpr. */ ! jtnode = parse-jointree; ! while (IsA(jtnode, FromExpr)) ! { ! if (list_length(jtnode-fromlist) != 1) ! return NULL; ! jtnode = linitial(jtnode-fromlist); ! } ! if (!IsA(jtnode, RangeTblRef)) return NULL; + rtr = (RangeTblRef *) jtnode; rte = rt_fetch(rtr-rtindex, parse-rtable); if (rte-rtekind != RTE_RELATION || rte-inh) return NULL; ---(end of broadcast)--- TIP 2: Don't 'kill -9' the postmaster ---(end of broadcast)--- TIP 1: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly
[PERFORM] index scan through a subquery
Why should these queries have different plans? create table foo (a int PRIMARY KEY); Q1: explain select max(a) from foo Result (cost=0.04..0.05 rows=1 width=0) InitPlan - Limit (cost=0.00..0.04 rows=1 width=4) - Index Scan Backward using foo_pkey on foo (cost=0.00..76.10 rows=2140 width=4) Filter: (a IS NOT NULL) Q2: explain select max(a) from (select * from foo) as f Aggregate (cost=36.75..36.76 rows=1 width=4) - Seq Scan on foo (cost=0.00..31.40 rows=2140 width=4) I need the lovely index scan, but my table is hidden behind a view, and all I get is the ugly sequential scan. Any ideas on how to convince the optimizer to unfold the subquery properly? Bill ---(end of broadcast)--- TIP 4: Have you searched our list archives? http://archives.postgresql.org
Re: [PERFORM] index scan through a subquery
Bill Howe [EMAIL PROTECTED] writes: I need the lovely index scan, but my table is hidden behind a view, and all I get is the ugly sequential scan. Any ideas on how to convince the optimizer to unfold the subquery properly? You should provide some context in this sort of gripe, like which PG version you're using. But I'm going to guess that it's 8.2.x, because 8.1.x gets it right :-(. Try the attached. regards, tom lane Index: planagg.c === RCS file: /cvsroot/pgsql/src/backend/optimizer/plan/planagg.c,v retrieving revision 1.25 diff -c -r1.25 planagg.c *** planagg.c 9 Jan 2007 02:14:13 - 1.25 --- planagg.c 6 Feb 2007 06:30:23 - *** *** 70,75 --- 70,76 optimize_minmax_aggregates(PlannerInfo *root, List *tlist, Path *best_path) { Query *parse = root-parse; + FromExpr *jtnode; RangeTblRef *rtr; RangeTblEntry *rte; RelOptInfo *rel; *** *** 102,115 * We also restrict the query to reference exactly one table, since join * conditions can't be handled reasonably. (We could perhaps handle a * query containing cartesian-product joins, but it hardly seems worth the !* trouble.) */ ! Assert(parse-jointree != NULL IsA(parse-jointree, FromExpr)); ! if (list_length(parse-jointree-fromlist) != 1) ! return NULL; ! rtr = (RangeTblRef *) linitial(parse-jointree-fromlist); ! if (!IsA(rtr, RangeTblRef)) return NULL; rte = rt_fetch(rtr-rtindex, parse-rtable); if (rte-rtekind != RTE_RELATION || rte-inh) return NULL; --- 103,121 * We also restrict the query to reference exactly one table, since join * conditions can't be handled reasonably. (We could perhaps handle a * query containing cartesian-product joins, but it hardly seems worth the !* trouble.) However, the single real table could be buried in several !* levels of FromExpr. */ ! jtnode = parse-jointree; ! while (IsA(jtnode, FromExpr)) ! { ! if (list_length(jtnode-fromlist) != 1) ! return NULL; ! jtnode = linitial(jtnode-fromlist); ! } ! if (!IsA(jtnode, RangeTblRef)) return NULL; + rtr = (RangeTblRef *) jtnode; rte = rt_fetch(rtr-rtindex, parse-rtable); if (rte-rtekind != RTE_RELATION || rte-inh) return NULL; ---(end of broadcast)--- TIP 2: Don't 'kill -9' the postmaster