From: drh <>
Date: Sun, 26 Jan 2025 20:09:57 +0000 (+0000)
Subject: Further comment improvements in the star-query heuristic.  Add an ALWAYS()
X-Git-Tag: version-3.49.0~52
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=2228567ad33a41951fc79205d5555c51f7881562;p=thirdparty%2Fsqlite.git

Further comment improvements in the star-query heuristic.  Add an ALWAYS()
on an unreachable branch to achieve MC/DC.

FossilOrigin-Name: 5e18ce68fbc5e73e6694936f3ba71f5b5e3758cf380951805ca6ea6a3f0943aa
---

diff --git a/manifest b/manifest
index e2dc85219e..7bdfce7763 100644
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C Small\ssize\sand\scomplexity\sreduction\son\sthe\sstar-query\sheuristic.\s\sImproved\ncomments\sfor\sthe\sstar-query\sheuristic.
-D 2025-01-26T17:29:33.018
+C Further\scomment\simprovements\sin\sthe\sstar-query\sheuristic.\s\sAdd\san\sALWAYS()\non\san\sunreachable\sbranch\sto\sachieve\sMC/DC.
+D 2025-01-26T20:09:57.061
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F LICENSE.md e108e1e69ae8e8a59e93c455654b8ac9356a11720d3345df2a4743e9590fb20d
@@ -863,7 +863,7 @@ F src/vxworks.h d2988f4e5a61a4dfe82c6524dd3d6e4f2ce3cdb9
 F src/wal.c 4e6181d8780ab0af2e1388d0754cbe6f2f04593d2b1ab6c41699a89942fd8997
 F src/wal.h ba252daaa94f889f4b2c17c027e823d9be47ce39da1d3799886bbd51f0490452
 F src/walker.c d5006d6b005e4ea7302ad390957a8d41ed83faa177e412f89bc5600a7462a014
-F src/where.c adda3afc98a4f58713973997c699be2a8515c591701092e8380695f1a0a7b220
+F src/where.c 72cd936dcaa391fdce021840fbd1d9cbe51e34f821e0a09a05a2cc99ab506e92
 F src/whereInt.h d20cddddb1d61b18d5cb1fcfa9b77fbeebbc4afe44d996e603452a23b3009ee1
 F src/wherecode.c 0c3d3199a2b769a5e2bb70feb5003dc85b3d86842ecaf903a47f2b4205ca5dab
 F src/whereexpr.c 0f93a29cabd3a338d09a1f5c6770620a1ac51ec1157f3229502a7e7767c60b6f
@@ -2208,8 +2208,8 @@ F tool/version-info.c 3b36468a90faf1bbd59c65fd0eb66522d9f941eedd364fabccd7227350
 F tool/warnings-clang.sh bbf6a1e685e534c92ec2bfba5b1745f34fb6f0bc2a362850723a9ee87c1b31a7
 F tool/warnings.sh 49a486c5069de041aedcbde4de178293e0463ae9918ecad7539eedf0ec77a139
 F tool/win/sqlite.vsix deb315d026cc8400325c5863eef847784a219a2f
-P 1bc09c9e8bd77ac41ecbe510c7e003757fc11d0f586da6cdf3584315aa9d6407
-R c0f75689e724495cafe203db572d7b59
+P a7ecb2f4b7eee78b88f1b2e026dffed2007ca4ffeb152632624ab2582839b250
+R 56a3a416133fa0f7166c060fc9c27138
 U drh
-Z 5884f43bd01d477b04985ecdd4572f42
+Z a3e111b0c87ac0b331649395aaa39e29
 # Remove this line to create a well-formed Fossil manifest.
diff --git a/manifest.uuid b/manifest.uuid
index 22688c5390..fbc82e399e 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-a7ecb2f4b7eee78b88f1b2e026dffed2007ca4ffeb152632624ab2582839b250
+5e18ce68fbc5e73e6694936f3ba71f5b5e3758cf380951805ca6ea6a3f0943aa
diff --git a/src/where.c b/src/where.c
index 01f8ff0d9a..8f467e9787 100644
--- a/src/where.c
+++ b/src/where.c
@@ -5519,10 +5519,9 @@ static int computeMxChoice(WhereInfo *pWInfo){
 
     pWInfo->bStarDone = 1; /* Only do this computation once */
 
-    /* Check to see if we are dealing with a star schema and if so, adjust
-    ** SCAN cost of dimensino tables so that they are as large as the SCAN
-    ** cost of the fact table.  This is a heuristic that helps keep the
-    ** fact tables in outer loops.
+    /* Look for fact tables with four or more dimensions where the
+    ** dimension tables are not separately from the fact tables by an outer
+    ** or cross join.  Adjust cost weights if found.
     */
     assert( !pWInfo->bStarUsed );
     aFromTabs = pWInfo->pTabList->a;
@@ -5539,7 +5538,7 @@ static int computeMxChoice(WhereInfo *pWInfo){
         ** restrict the search for dimension-tables to be tables to the right
         ** of the fact-table. */
         if( iFromIdx+4 > nLoop ) break;  /* Impossible to reach nDep>=4 */
-        while( pStart && pStart->iTab<=iFromIdx ){
+        while( ALWAYS(pStart) && pStart->iTab<=iFromIdx ){
           pStart = pStart->pNextLoop;
         }
       }
@@ -5563,7 +5562,10 @@ static int computeMxChoice(WhereInfo *pWInfo){
         }
       }
       if( nDep<=3 ) continue;
-      /* If we reach this point, it means that pFactTab is a fact table */
+
+      /* If we reach this point, it means that pFactTab is a fact table
+      ** with four or more dimensions connected by inner joins.  Proceed
+      ** to make cost adjustments. */
      
 #ifdef WHERETRACE_ENABLED
       /* Make sure rStarDelta values are initialized */
@@ -5575,8 +5577,8 @@ static int computeMxChoice(WhereInfo *pWInfo){
 #endif
       pWInfo->bStarUsed = 1;
 
-      /* Compute one more than the maximum cost of any WhereLoop for the
-      ** fact table */
+      /* Compute the maximum cost of any WhereLoop for the
+      ** fact table plus one epsilon */
       mxRun = LOGEST_MIN;
       for(pWLoop=pStart; pWLoop; pWLoop=pWLoop->pNextLoop){
         if( pWLoop->iTab<iFromIdx ) continue;
@@ -5585,8 +5587,8 @@ static int computeMxChoice(WhereInfo *pWInfo){
       }
       if( ALWAYS(mxRun<LOGEST_MAX) ) mxRun++;
 
-      /* Increase the cost of table scans for dimension tables to be slightly
-      ** more than the maximum cost of fact table */
+      /* Increase the cost of table scans for dimension tables to be
+      ** slightly more than the maximum cost of the fact table */
       for(pWLoop=pStart; pWLoop; pWLoop=pWLoop->pNextLoop){
         if( (pWLoop->maskSelf & mSeen)==0 ) continue;
         if( pWLoop->nLTerm ) continue;