X-Original-To: pgsql-performance-postgresql.org@localhost.postgresql.org Received: from localhost (mx2.hub.org [200.46.204.254]) by postgresql.org (Postfix) with ESMTP id E78F111F6C47 for ; Fri, 14 Apr 2006 13:04:44 -0300 (ADT) X-Virus-Scanned: by amavisd-new at hub.org X-Spam-Score: -1.215 X-Spam-Level: X-Spam-Status: No, score=-1.215 required=5 tests=[BAYES_00=-2.599, SPF_SOFTFAIL=1.384] Received: from postgresql.org ([200.46.204.71]) by localhost (mx2.hub.org [200.46.204.254]) (amavisd-new, port 10024) with ESMTP id t+ekWY+CJ4xf for ; Fri, 14 Apr 2006 13:04:30 -0300 (ADT) X-Greylist: delayed 00:27:27.563451 by SQLgrey- Received: from svr4.postgresql.org (svr4.postgresql.org [66.98.251.159]) by postgresql.org (Postfix) with ESMTP id 8838911F6CA2 for ; Fri, 14 Apr 2006 13:04:24 -0300 (ADT) Received: from mailhost.intellivid.com (mailhost.intellivid.com [64.32.200.11]) by svr4.postgresql.org (Postfix) with ESMTP id 8EA395AF0A1 for ; Fri, 14 Apr 2006 15:36:54 +0000 (GMT) Received: from spectre.intellivid.com (spectre.intellivid.com [192.168.2.68]) (using TLSv1 with cipher RC4-MD5 (128/128 bits)) (Client did not present a certificate) by newmail.intellivid.com (Postfix) with ESMTP id 435C6F1814F for ; Fri, 14 Apr 2006 11:36:49 -0400 (EDT) Subject: merge>hash>loop From: Ian Westmacott To: pgsql-performance@postgresql.org Content-Type: text/plain Organization: IntelliVid Corp. Date: Fri, 14 Apr 2006 11:36:48 -0400 Message-Id: <1145029009.3422.31.camel@spectre.intellivid.com> Mime-Version: 1.0 X-Mailer: Evolution 2.4.1 Content-Transfer-Encoding: 7bit X-Archive-Number: 200604/334 X-Sequence-Number: 18418 I have this query, where PG (8.1.2) prefers Merge Join over Hash Join over Nested Loop. However, this order turns out to increase in performance. I was hoping someone might be able to shed some light on why PG chooses the plans in this order, and what I might do to influence it otherwise. Thanks, itvtrackdata=> explain analyze SELECT mva,blob.* FROM blobs00000000000033c3_c16010 AS blob NATURAL JOIN objects00000000000033c3 WHERE AREA(BOX(POINT(bbox_x1,bbox_y0),POINT(bbox_x0,bbox_y1))#BOX('(50,10),(10,50)'))/AREA(BOX(POINT(bbox_x1,bbox_y0),POINT(bbox_x0,bbox_y1)))>0 AND time>=1263627787-32768 AND time<1273458187 AND finish-start>=8738 ORDER BY time ASC; QUERY PLAN ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Sort (cost=47170.44..47184.46 rows=5607 width=28) (actual time=2661.980..2663.642 rows=1687 loops=1) Sort Key: blob."time" -> Merge Join (cost=46547.88..46821.32 rows=5607 width=28) (actual time=2645.685..2657.621 rows=1687 loops=1) Merge Cond: ("outer".sva = "inner".sva) -> Sort (cost=18003.31..18045.36 rows=16821 width=20) (actual time=181.303..183.092 rows=1741 loops=1) Sort Key: blob.sva -> Bitmap Heap Scan on blobs00000000000033c3_c16010 blob (cost=535.77..16822.65 rows=16821 width=20) (actual time=10.827..177.671 rows=1741 loops=1) Recheck Cond: (("time" >= 1263595019) AND ("time" < 1273458187)) Filter: ((area((box(point((bbox_x1)::double precision, (bbox_y0)::double precision), point((bbox_x0)::double precision, (bbox_y1)::double precision)) # '(50,50),(10,10)'::box)) / area(box(point((bbox_x1)::double precision, (bbox_y0)::double precision), point((bbox_x0)::double precision, (bbox_y1)::double precision)))) > 0::double precision) -> Bitmap Index Scan on idx_blobs00000000000033c3_c16010_time (cost=0.00..535.77 rows=50462 width=0) (actual time=8.565..8.565 rows=50673 loops=1) Index Cond: (("time" >= 1263595019) AND ("time" < 1273458187)) -> Sort (cost=28544.56..28950.88 rows=162526 width=16) (actual time=2387.726..2437.429 rows=29969 loops=1) Sort Key: objects00000000000033c3.sva -> Seq Scan on objects00000000000033c3 (cost=0.00..14477.68 rows=162526 width=16) (actual time=0.085..826.125 rows=207755 loops=1) Filter: ((finish - "start") >= 8738) Total runtime: 2675.037 ms (16 rows) itvtrackdata=> set enable_mergejoin to false; SET itvtrackdata=> explain analyze SELECT mva,blob.* FROM blobs00000000000033c3_c16010 AS blob NATURAL JOIN objects00000000000033c3 WHERE AREA(BOX(POINT(bbox_x1,bbox_y0),POINT(bbox_x0,bbox_y1))#BOX('(50,10),(10,50)'))/AREA(BOX(POINT(bbox_x1,bbox_y0),POINT(bbox_x0,bbox_y1)))>0 AND time>=1263627787-32768 AND time<1273458187 AND finish-start>=8738 ORDER BY time ASC; QUERY PLAN ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Sort (cost=65783.09..65797.10 rows=5607 width=28) (actual time=1211.228..1212.671 rows=1687 loops=1) Sort Key: blob."time" -> Hash Join (cost=15419.77..65433.97 rows=5607 width=28) (actual time=1067.514..1207.727 rows=1687 loops=1) Hash Cond: ("outer".sva = "inner".sva) -> Bitmap Heap Scan on blobs00000000000033c3_c16010 blob (cost=535.77..16822.65 rows=16821 width=20) (actual time=14.720..149.179 rows=1741 loops=1) Recheck Cond: (("time" >= 1263595019) AND ("time" < 1273458187)) Filter: ((area((box(point((bbox_x1)::double precision, (bbox_y0)::double precision), point((bbox_x0)::double precision, (bbox_y1)::double precision)) # '(50,50),(10,10)'::box)) / area(box(point((bbox_x1)::double precision, (bbox_y0)::double precision), point((bbox_x0)::double precision, (bbox_y1)::double precision)))) > 0::double precision) -> Bitmap Index Scan on idx_blobs00000000000033c3_c16010_time (cost=0.00..535.77 rows=50462 width=0) (actual time=12.880..12.880 rows=50673 loops=1) Index Cond: (("time" >= 1263595019) AND ("time" < 1273458187)) -> Hash (cost=14477.68..14477.68 rows=162526 width=16) (actual time=1052.729..1052.729 rows=207755 loops=1) -> Seq Scan on objects00000000000033c3 (cost=0.00..14477.68 rows=162526 width=16) (actual time=0.028..684.047 rows=207755 loops=1) Filter: ((finish - "start") >= 8738) Total runtime: 1217.938 ms (13 rows) itvtrackdata=> set enable_hashjoin to false; SET itvtrackdata=> explain analyze SELECT mva,blob.* FROM blobs00000000000033c3_c16010 AS blob NATURAL JOIN objects00000000000033c3 WHERE AREA(BOX(POINT(bbox_x1,bbox_y0),POINT(bbox_x0,bbox_y1))#BOX('(50,10),(10,50)'))/AREA(BOX(POINT(bbox_x1,bbox_y0),POINT(bbox_x0,bbox_y1)))>0 AND time>=1263627787-32768 AND time<1273458187 AND finish-start>=8738 ORDER BY time ASC; QUERY PLAN ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Sort (cost=118258.49..118272.51 rows=5607 width=28) (actual time=197.204..198.871 rows=1687 loops=1) Sort Key: blob."time" -> Nested Loop (cost=535.77..117909.37 rows=5607 width=28) (actual time=27.560..192.526 rows=1687 loops=1) -> Bitmap Heap Scan on blobs00000000000033c3_c16010 blob (cost=535.77..16822.65 rows=16821 width=20) (actual time=27.450..157.266 rows=1741 loops=1) Recheck Cond: (("time" >= 1263595019) AND ("time" < 1273458187)) Filter: ((area((box(point((bbox_x1)::double precision, (bbox_y0)::double precision), point((bbox_x0)::double precision, (bbox_y1)::double precision)) # '(50,50),(10,10)'::box)) / area(box(point((bbox_x1)::double precision, (bbox_y0)::double precision), point((bbox_x0)::double precision, (bbox_y1)::double precision)))) > 0::double precision) -> Bitmap Index Scan on idx_blobs00000000000033c3_c16010_time (cost=0.00..535.77 rows=50462 width=0) (actual time=24.445..24.445 rows=50673 loops=1) Index Cond: (("time" >= 1263595019) AND ("time" < 1273458187)) -> Index Scan using idx_objects00000000000033c3_sva on objects00000000000033c3 (cost=0.00..6.00 rows=1 width=16) (actual time=0.013..0.015 rows=1 loops=1741) Index Cond: ("outer".sva = objects00000000000033c3.sva) Filter: ((finish - "start") >= 8738) Total runtime: 200.719 ms (12 rows) -- Ian Westmacott IntelliVid Corp.