Fix typos in comments. Provided ".wheretrace" debugging output for the

interstage heuristic module.  Do omit automatic index loops in the
interstage heuristic.

FossilOrigin-Name: 186dcae19e249db36de15f295999cff25063b54ee3d5d481cd2ba99b6d13148e

2 files changed, 20 insertions, 5 deletions

diff --git a/src/sqliteInt.h b/src/sqliteInt.h
index dba64c71b..365ff2c7f 100644
--- a/src/sqliteInt.h
+++ b/src/sqliteInt.h
@@ -1156,7 +1156,7 @@ extern u32 sqlite3WhereTrace;
 ** 0x00000010   Display sqlite3_index_info xBestIndex calls
 ** 0x00000020   Range an equality scan metrics
 ** 0x00000040   IN operator decisions
-** 0x00000080   WhereLoop cost adjustements
+** 0x00000080   WhereLoop cost adjustments
 ** 0x00000100
 ** 0x00000200   Covering index decisions
 ** 0x00000400   OR optimization
diff --git a/src/where.c b/src/where.c
index fe76f2c96..a4506602a 100644
--- a/src/where.c
+++ b/src/where.c
@@ -5561,15 +5561,15 @@ static int wherePathSolver(WhereInfo *pWInfo, LogEst nRowEst){
 ** Except, if the first solver() call generated a full-table scan in an outer
 ** loop then stop this analysis at the first full-scan, since the second
 ** solver() run might try to swap that full-scan for another in order to
-** get the output into the correct order.  In other words, we do *not* want
-** to inhibit a rewrites like this:
+** get the output into the correct order.  In other words, we allow a
+** rewrite like this:
 **
 **     First Solver()                      Second Solver()
 **       |-- SCAN t1                         |-- SCAN t2
 **       |-- SEARCH t2                       `-- SEARCH t1
 **       `-- SORT USING B-TREE
 **
-** Rather, the purpose of this routine is to inhibit rewrites such as:
+** The purpose of this routine is to disallow rewrites such as:
 **
 **     First Solver()                      Second Solver()
 **       |-- SEARCH t1                       |-- SCAN t2     <--- bad!
@@ -5581,6 +5581,9 @@ static int wherePathSolver(WhereInfo *pWInfo, LogEst nRowEst){
 */
 static SQLITE_NOINLINE void whereInterstageHeuristic(WhereInfo *pWInfo){
   int i;
+#ifdef WHERETRACE_ENABLED
+  int once = 0;
+#endif
   for(i=0; i<pWInfo->nLevel; i++){
     WhereLoop *p = pWInfo->a[i].pWLoop;
     if( p==0 ) break;
@@ -5590,7 +5593,19 @@ static SQLITE_NOINLINE void whereInterstageHeuristic(WhereInfo *pWInfo){
       WhereLoop *pLoop;
       for(pLoop=pWInfo->pLoops; pLoop; pLoop=pLoop->pNextLoop){
         if( pLoop->iTab!=iTab ) continue;
-        if( (pLoop->wsFlags & WHERE_CONSTRAINT)!=0 ) continue;
+        if( (pLoop->wsFlags & (WHERE_CONSTRAINT|WHERE_AUTO_INDEX))!=0 ){
+          /* Auto-index and index-constrained loops allowed to remain */
+          continue;
+        }
+#ifdef WHERETRACE_ENABLED
+        if( sqlite3WhereTrace & 0x80 ){
+          if( once==0 ){
+            sqlite3DebugPrintf("Loops disabled by interstage heuristic:\n");
+            once = 1;
+          }
+          sqlite3WhereLoopPrint(pLoop, &pWInfo->sWC);
+        }
+#endif /* WHERETRACE_ENABLED */
         pLoop->prereq = ALLBITS;  /* Prevent 2nd solver() from using this one */
       }
     }else{