From: drh <>
Date: Fri, 15 Sep 2023 19:00:47 +0000 (+0000)
Subject: Do not reduce subquery output row count estimates due to DISTINCT until
X-Git-Tag: version-3.44.0~194^2~1
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=c09701db9b7c63fe10f8cc2e8ef89ec33b28351e;p=thirdparty%2Fsqlite.git

Do not reduce subquery output row count estimates due to DISTINCT until
after the decision of whether or not to use an index for ORDER BY has been
made.

FossilOrigin-Name: 27390051e86ad86fb35219329d359be9e83073f59782631af7fc519225e10565
---

diff --git a/manifest b/manifest
index b30bf290dd..510c5900c5 100644
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C Experimental:\s\sAssume\sthat\sa\sDISTINCT\sclause\son\sa\ssubquery\sreduces\sthe\snumber\nof\srows\sreturned\sby\sthat\ssubquery\sby\sa\sfactor\sof\s8.
-D 2023-09-15T16:15:33.055
+C Do\snot\sreduce\ssubquery\soutput\srow\scount\sestimates\sdue\sto\sDISTINCT\suntil\nafter\sthe\sdecision\sof\swhether\sor\snot\sto\suse\san\sindex\sfor\sORDER\sBY\shas\sbeen\nmade.
+D 2023-09-15T19:00:47.376
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
@@ -795,7 +795,7 @@ F src/vxworks.h d2988f4e5a61a4dfe82c6524dd3d6e4f2ce3cdb9
 F src/wal.c 01e051a1e713d9eabdb25df38602837cec8f4c2cae448ce2cf6accc87af903e9
 F src/wal.h ba252daaa94f889f4b2c17c027e823d9be47ce39da1d3799886bbd51f0490452
 F src/walker.c 7c7ea0115345851c3da4e04e2e239a29983b61fb5b038b94eede6aba462640e2
-F src/where.c 6cdf686c80cea6bf01983714e8fa291976072429dc3d5f9f0ee63340ff31c20a
+F src/where.c bd10b322a40abc2ebfba61fd1f3c434052f68cf991487c4ed1da9c9f94aa0e87
 F src/whereInt.h 4b38c5889514e3aead3f27d0ee9a26e47c3f150efc59e2a8b4e3bc8835e4d7a1
 F src/wherecode.c 5d77db30a2a3dd532492ae882de114edba2fae672622056b1c7fd61f5917a8f1
 F src/whereexpr.c dc5096eca5ed503999be3bdee8a90c51361289a678d396a220912e9cb73b3c00
@@ -1602,7 +1602,7 @@ F test/stmtvtab1.test 6873dfb24f8e79cbb5b799b95c2e4349060eb7a3b811982749a84b3594
 F test/strict1.test 4d2b492152b984fd7e8196d23eb88e2ccb0ef9e46ca2f96c2ce7147ceef9d168
 F test/strict2.test b22c7a98b5000aef937f1990776497f0e979b1a23bc4f63e2d53b00e59b20070
 F test/subjournal.test 8d4e2572c0ee9a15549f0d8e40863161295107e52f07a3e8012a2e1fdd093c49
-F test/subquery.test 3a1a5b600b8d4f504d2a2c61f33db820983dba94a0ef3e4aedca8f0165eaecb8
+F test/subquery.test 312c5d26304b0e93a56ba2cb9d4480b8a1c8217e3b2b8f8be2bfb0b2458ac3a7
 F test/subquery2.test 90cf944b9de8204569cf656028391e4af1ccc8c0cc02d4ef38ee3be8de1ffb12
 F test/subselect.test 0966aa8e720224dbd6a5e769a3ec2a723e332303
 F test/substr.test a673e3763e247e9b5e497a6cacbaf3da2bd8ec8921c0677145c109f2e633f36b
@@ -2121,8 +2121,8 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P d9625a9eafe88859c3255849ee750cc6322d5a13ddad45107f9b2085c20eff50
-R 4ef1ee11935ce0c2e4bd33d7caf58576
+P 5a940e47d501f23347eaf084f4820e064e93665d19c8938c80715b71006ede8b
+R 708ef68b1a5a2dad2e7d5b5c554e468e
 U drh
-Z 02839c7f0b57c458709ba0da92bf6fc7
+Z 3822ece14e8e4a55dc3118a267231484
 # Remove this line to create a well-formed Fossil manifest.
diff --git a/manifest.uuid b/manifest.uuid
index 588208a82a..139acb4f86 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-5a940e47d501f23347eaf084f4820e064e93665d19c8938c80715b71006ede8b
\ No newline at end of file
+27390051e86ad86fb35219329d359be9e83073f59782631af7fc519225e10565
\ No newline at end of file
diff --git a/src/where.c b/src/where.c
index 79ec7f6901..c10ab27a88 100644
--- a/src/where.c
+++ b/src/where.c
@@ -5353,15 +5353,6 @@ static int wherePathSolver(WhereInfo *pWInfo, LogEst nRowEst){
 
   pWInfo->nRowOut = pFrom->nRow;
 
-  /* TUNING:  Assume that a DISTINCT clause on a subquery reduces
-  ** the output size by a factor of 8 (LogEst -30)
-  */
-  if( (pWInfo->wctrlFlags & WHERE_WANT_DISTINCT)!=0
-   && pWInfo->nRowOut>30
-  ){
-    pWInfo->nRowOut -= 30;
-  }
-
   /* Free temporary memory and return success */
   sqlite3StackFreeNN(pParse->db, pSpace);
   return SQLITE_OK;
@@ -6141,6 +6132,18 @@ WhereInfo *sqlite3WhereBegin(
        wherePathSolver(pWInfo, pWInfo->nRowOut+1);
        if( db->mallocFailed ) goto whereBeginError;
     }
+
+    /* TUNING:  Assume that a DISTINCT clause on a subquery reduces
+    ** the output size by a factor of 8 (LogEst -30)
+    */
+    if( (pWInfo->wctrlFlags & WHERE_WANT_DISTINCT)!=0
+     && pWInfo->nRowOut>=40
+    ){
+      WHERETRACE(0x0080,("nRowOut reduced from %d to %d due to DISTINCT\n",
+                         pWInfo->nRowOut, pWInfo->nRowOut-30));
+      pWInfo->nRowOut -= 30;
+    }
+
   }
   assert( pWInfo->pTabList!=0 );
   if( pWInfo->pOrderBy==0 && (db->flags & SQLITE_ReverseOrder)!=0 ){
diff --git a/test/subquery.test b/test/subquery.test
index a048f9ed4e..c51edba040 100644
--- a/test/subquery.test
+++ b/test/subquery.test
@@ -11,8 +11,6 @@
 # This file implements regression tests for SQLite library.  The
 # focus of this script is testing correlated subqueries
 #
-# $Id: subquery.test,v 1.17 2009/01/09 01:12:28 drh Exp $
-#
 
 set testdir [file dirname $argv0]
 source $testdir/tester.tcl
@@ -613,4 +611,45 @@ do_execsql_test subquery-9.4 {
   SELECT (SELECT DISTINCT x FROM t1 ORDER BY +x LIMIT 1 OFFSET 2) FROM t1;
 } {{} {} {} {}}
 
+# 2023-09-15
+# Query planner performance regression reported by private email 
+# on 2023-09-14, caused by VIEWSCAN optimization of check-in 609fbb94b8f01d67
+# from 2022-09-01.
+#
+reset_db
+do_execsql_test subquery-10.1 {
+  CREATE TABLE t1(aa TEXT, bb INT, cc TEXT);
+  CREATE INDEX x11 on t1(bb);
+  CREATE INDEX x12 on t1(aa);
+  CREATE TABLE t2(aa TEXT, xx INT);
+  ANALYZE sqlite_master;
+  INSERT INTO sqlite_stat1(tbl, idx, stat) VALUES('t1', 'x11', '156789 28');
+  INSERT INTO sqlite_stat1(tbl, idx, stat) VALUES('t1', 'x12', '156789 1');
+  ANALYZE sqlite_master;
+}
+do_eqp_test subquery-10.2 {
+  WITH v1(aa,cc,bb) AS (SELECT aa, cc, bb FROM t1 WHERE bb=12345),
+       v2(aa,mx)    AS (SELECT aa, max(xx) FROM t2 GROUP BY aa)
+  SELECT * FROM v1 JOIN v2 ON v1.aa=v2.aa;
+} {
+  QUERY PLAN
+  |--CO-ROUTINE v2
+  |  |--SCAN t2
+  |  `--USE TEMP B-TREE FOR GROUP BY
+  |--SEARCH t1 USING INDEX x11 (bb=?)
+  `--SEARCH v2 USING AUTOMATIC COVERING INDEX (aa=?)
+}
+# ^^^^^^^^^^^^^
+# Prior to the fix the incorrect (slow) plan caused by the
+# VIEWSCAN optimization was:
+#
+# QUERY PLAN
+# |--CO-ROUTINE v2
+# |  |--SCAN t2
+# |  `--USE TEMP B-TREE FOR GROUP BY
+# |--SCAN v2
+# `--SEARCH t1 USING INDEX x12 (aa=?)
+#
+
+
 finish_test