From: drh <>
Date: Mon, 27 May 2024 21:55:01 +0000 (+0000)
Subject: Avoid creating an automatic index on a column that is known to be not very
X-Git-Tag: version-3.47.0~377^2
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=refs%2Fheads%2Fauto-index-improvements;p=thirdparty%2Fsqlite.git

Avoid creating an automatic index on a column that is known to be not very
selective.

FossilOrigin-Name: 70409763f70faa2a0f4f072fd318a687b109a0905cc57906ad7f80d2885fe6d9
---

diff --git a/manifest b/manifest
index 4e2cea56dd..d844021f66 100644
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C The\sprevious\scheck-in\swas\sa\slittle\stwo\saggressive\sabout\sskipping\sthe\ninitialization\sof\sentries\sin\sthe\sCellArray.ixNx\sarray.\s\sFixed\shere.
-D 2024-05-27T19:52:24.258
+C Avoid\screating\san\sautomatic\sindex\son\sa\scolumn\sthat\sis\sknown\sto\sbe\snot\svery\nselective.
+D 2024-05-27T21:55:01.258
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
@@ -840,7 +840,7 @@ F src/vxworks.h d2988f4e5a61a4dfe82c6524dd3d6e4f2ce3cdb9
 F src/wal.c 887fc4ca3f020ebb2e376f222069570834ac63bf50111ef0cbf3ae417048ed89
 F src/wal.h ba252daaa94f889f4b2c17c027e823d9be47ce39da1d3799886bbd51f0490452
 F src/walker.c 7c7ea0115345851c3da4e04e2e239a29983b61fb5b038b94eede6aba462640e2
-F src/where.c 9b2ab23fcc2198ebcee1e6e840a9ff22350668bd3a99195a5dc7299d5908370a
+F src/where.c 555c75e91b44b8f575579eea4f2cf86c419ab4e79e44ce546e399a60cd3020e2
 F src/whereInt.h 82a13766f13d1a53b05387c2e60726289ef26404bc7b9b1f7770204d97357fb8
 F src/wherecode.c d5184620bcb5265d59072cb66e1386bfe0331a9ce7614286f9ab79a4fcd00fb8
 F src/whereexpr.c 67d15caf88a1a9528283d68ff578e024cf9fe810b517bb0343e5aaf695ad97dd
@@ -910,7 +910,7 @@ F test/autoanalyze1.test b9cc3f32a990fa56669b668d237c6d53e983554ae80c0604992e188
 F test/autoinc.test 997d6f185f138229dc4251583a1d04816423dddc2fc034871a01aeb1d728cb39
 F test/autoindex1.test d34caffb0384003ee28eae87679214c029e9be4b332d9649a79e0b94ab70502c
 F test/autoindex2.test 12ef578928102baaa0dc23ad397601a2f4ecb0df
-F test/autoindex3.test dcd6b2f8bed2be67b131e2e671f892e971d934e24fd00988952d0e0a67e24aa7
+F test/autoindex3.test ca502c8050166ac6107a7b4fe4e951f4d3270a23a958af02b14f1b962b83c4b6
 F test/autoindex4.test 3c2105e9172920e26f950ba3c5823e4972190e022c1e6f260ba476b0af24c593
 F test/autoindex5.test 2ee94f033b87ca0160e08d81034c507aff8e230df2627f0304fa309b2fee19a3
 F test/autovacuum.test 00671369bbf96c6a49989a9425f5b78b94075d6a4b031e5e00000c2c32f365df
@@ -2193,8 +2193,11 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P 428aadf0c71473ccb0681b2b7146281c62949ee99556873e49895d44eec7aee5
-R 4ca5c510c21258f08a4799ee1f04b980
+P 1b6d1fbcdecf14bc79dc7b5df50e585d2fcc1484a9987b863c190e8f7ba2c39f
+R 33d42e8c7f39f01a63aa7a9a3cae7431
+T *branch * auto-index-improvements
+T *sym-auto-index-improvements *
+T -sym-trunk *
 U drh
-Z e77b6b7828b797641ee06ff1dc47219a
+Z ae3dc9b91b8cb58bdaacbf4b44d36f22
 # Remove this line to create a well-formed Fossil manifest.
diff --git a/manifest.uuid b/manifest.uuid
index 1de423f654..0233074f46 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-1b6d1fbcdecf14bc79dc7b5df50e585d2fcc1484a9987b863c190e8f7ba2c39f
\ No newline at end of file
+70409763f70faa2a0f4f072fd318a687b109a0905cc57906ad7f80d2885fe6d9
\ No newline at end of file
diff --git a/src/where.c b/src/where.c
index a266b51d03..accad86251 100644
--- a/src/where.c
+++ b/src/where.c
@@ -840,6 +840,40 @@ static int constraintCompatibleWithOuterJoin(
   return 1;
 }
 
+#ifndef SQLITE_OMIT_AUTOMATIC_INDEX
+/*
+** Return true if column iCol of table pTab seem like it might be a
+** good column to use as part of a query-time index.
+**
+** Current algorithm (subject to improvement!):
+**
+**   1.   If iCol is already the left-most column of some other index,
+**        then return false.
+**
+**   2.   If iCol is part of an existing index that has an aiRowLogEst of
+**        more than 20, then return false.
+**
+**   3.   If no disqualifying conditions above are found, return true.
+*/
+static SQLITE_NOINLINE int columnIsGoodIndexCandidate(
+  const Table *pTab,
+  int iCol
+){
+  const Index *pIdx;
+  for(pIdx = pTab->pIndex; pIdx!=0; pIdx=pIdx->pNext){
+    int j;
+    for(j=0; j<pIdx->nKeyCol; j++){
+       if( pIdx->aiColumn[j]==iCol ){
+         if( j==0 ) return 0;
+         if( pIdx->hasStat1 && pIdx->aiRowLogEst[j+1]>20 ) return 0;
+         break;
+       }
+    }
+  }
+  return 1;
+}
+#endif /* SQLITE_OMIT_AUTOMATIC_INDEX */
+
 
 
 #ifndef SQLITE_OMIT_AUTOMATIC_INDEX
@@ -854,6 +888,8 @@ static int termCanDriveIndex(
   const Bitmask notReady         /* Tables in outer loops of the join */
 ){
   char aff;
+  int leftCol;
+  
   if( pTerm->leftCursor!=pSrc->iCursor ) return 0;
   if( (pTerm->eOperator & (WO_EQ|WO_IS))==0 ) return 0;
   assert( (pSrc->fg.jointype & JT_RIGHT)==0 );
@@ -864,11 +900,12 @@ static int termCanDriveIndex(
   }
   if( (pTerm->prereqRight & notReady)!=0 ) return 0;
   assert( (pTerm->eOperator & (WO_OR|WO_AND))==0 );
-  if( pTerm->u.x.leftColumn<0 ) return 0;
-  aff = pSrc->pTab->aCol[pTerm->u.x.leftColumn].affinity;
+  leftCol = pTerm->u.x.leftColumn;
+  if( leftCol<0 ) return 0;
+  aff = pSrc->pTab->aCol[leftCol].affinity;
   if( !sqlite3IndexAffinityOk(pTerm->pExpr, aff) ) return 0;
   testcase( pTerm->pExpr->op==TK_IS );
-  return 1;
+  return columnIsGoodIndexCandidate(pSrc->pTab, leftCol);
 }
 #endif
 
diff --git a/test/autoindex3.test b/test/autoindex3.test
index 3da7a70586..aa6aa00128 100644
--- a/test/autoindex3.test
+++ b/test/autoindex3.test
@@ -90,5 +90,40 @@ do_eqp_test 220 {
   `--SEARCH u USING AUTOMATIC COVERING INDEX (b=?)
 }
 
+# 2024-05-27
+# ticket https://sqlite.org/src/tktview/8ff324e120
+# forum post https://sqlite.org/forum/forumpost/b21c2101a559be0a
+#
+# If an index with STAT1 data indicates that a column is not very
+# selective, then do not attempt to create an automatic index on
+# that column.
+#
+reset_db
+do_execsql_test 300 {
+  CREATE TABLE t1(id INTEGER PRIMARY KEY);
+  CREATE TABLE t2(cid INT, pid INT, rx INT, PRIMARY KEY(cid, pid, rx));
+  CREATE INDEX x1 ON t2(pid, rx);
+  ANALYZE sqlite_schema;
+  REPLACE INTO sqlite_stat1(tbl, idx, stat) VALUES
+    ('t2', 'x1', '500000 250 250'),
+    ('t2','sqlite_autoindex_t2_1','500000 1 1 1');
+  ANALYZE sqlite_schema;
+}
+do_eqp_test 310 {
+  WITH RECURSIVE children(id) AS (
+    SELECT cid FROM t2 WHERE pid = ?1 AND rx = ?2
+    UNION 
+    SELECT cid FROM t2 JOIN children ON t2.pid = children.id AND rx = ?2
+  ) SELECT count(id) FROM children;
+} {
+  QUERY PLAN
+  |--CO-ROUTINE children
+  |  |--SETUP
+  |  |  `--SEARCH t2 USING INDEX x1 (pid=? AND rx=?)
+  |  `--RECURSIVE STEP
+  |     |--SCAN children
+  |     `--SEARCH t2 USING INDEX x1 (pid=? AND rx=?)
+  `--SCAN children
+}  
 
 finish_test