Improve the performance of ANALYZE when SQLITE_ENABLE_STAT4 is defined.

FossilOrigin-Name: 737a82444065752785c643b1d29ca097c828effb

manifest

@@ -1,5 +1,5 @@
-C Improvements\sto\sPRAGMA\sintegrity_check.\nVerify\sCHECK\sconstraints.\nVerify\sNOT\sNULL\sconstraints\seven\son\stable\sthat\slack\sindexes.\nVerify\sCHECK\sand\sNOT\sNULL\sconstraints\swith\sPRAGMA\squick_check.
-D 2017-02-22T18:53:13.913
+C Improve\sthe\sperformance\sof\sANALYZE\swhen\sSQLITE_ENABLE_STAT4\sis\sdefined.
+D 2017-02-22T19:27:51.768
 F Makefile.in edb6bcdd37748d2b1c3422ff727c748df7ffe918
 F Makefile.linux-gcc 7bc79876b875010e8c8f9502eb935ca92aa3c434
 F Makefile.msc a89ea37ab5928026001569f056973b9059492fe2
@@ -332,7 +332,7 @@ F sqlite.pc.in 42b7bf0d02e08b9e77734a47798d1a55a9e0716b
 F sqlite3.1 fc7ad8990fc8409983309bb80de8c811a7506786
 F sqlite3.pc.in 48fed132e7cb71ab676105d2a4dc77127d8c1f3a
 F src/alter.c 3b23977620ce9662ac54443f65b87ba996e36121
-F src/analyze.c ac7a5d7e3cee07d074697904e00e4a8ab7b2b4f5
+F src/analyze.c 844359e720d1116592234f2f7938432bdc5b6238
 F src/attach.c 8c476f8bd5d2afe11d925f890d30e527e5b0ce43
 F src/auth.c 930b376a9c56998557367e6f7f8aaeac82a2a792
 F src/backup.c faf17e60b43233c214aae6a8179d24503a61e83b
@@ -1557,7 +1557,7 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P 80adc0cb4ed7bacc54b15ac8b5b205403939c8c4 5af7d72ed9ec758283d78ceb46627d72021c1c60
-R 46f90a15a015e3c65c6378dae6f8ff19
-U drh
-Z 9fac49478b578adef606b235c8c223db
+P aa02bd3c95e374008b930d296c88dfafaf11c65a
+R 767bcf2e23bb391de45c0ed55772662f
+U dan
+Z 11a6abc8e262f46553fa08a6e318d405

manifest.uuid

@@ -1 +1 @@
-aa02bd3c95e374008b930d296c88dfafaf11c65a
+737a82444065752785c643b1d29ca097c828effb

src/analyze.c

@@ -290,6 +290,7 @@ struct Stat4Accum {
   Stat4Sample *aBest;       /* Array of nCol best samples */
   int iMin;                 /* Index in a[] of entry with minimum score */
   int nSample;              /* Current number of samples */
+  int nMaxEqZero;           /* Max leading 0 in anEq[] for any a[] entry */
   int iGet;                 /* Index of current sample accessed by stat_get() */
   Stat4Sample *a;           /* Array of mxSample Stat4Sample objects */
   sqlite3 *db;              /* Database connection, for malloc() */
@@ -551,7 +552,14 @@ static void sampleInsert(Stat4Accum *p, Stat4Sample *pNew, int nEqZero){
   Stat4Sample *pSample = 0;
   int i;
 
+  /* Stat4Accum.nMaxEqZero is set to the maximum number of leading 0
+  ** values in the anEq[] array of any sample in Stat4Accum.a[]. In
+  ** other words, if nMaxEqZero is n, then it is guaranteed that there
+  ** are no samples with Stat4Sample.anEq[m]==0 for (m>=n). */
   assert( IsStat4 || nEqZero==0 );
+  if( nEqZero>p->nMaxEqZero ){
+    p->nMaxEqZero = nEqZero;
+  }
 
 #ifdef SQLITE_ENABLE_STAT4
   if( pNew->isPSample==0 ){
@@ -651,12 +659,22 @@ static void samplePushPrevious(Stat4Accum *p, int iChng){
     }
   }
 
-  /* Update the anEq[] fields of any samples already collected. */
+  /* Check that no sample contains an anEq[] entry with an index of
+  ** p->nMaxEqZero or greater set to zero. */
   for(i=p->nSample-1; i>=0; i--){
     int j;
-    for(j=iChng; j<p->nCol; j++){
-      if( p->a[i].anEq[j]==0 ) p->a[i].anEq[j] = p->current.anEq[j];
+    for(j=p->nMaxEqZero; j<p->nCol; j++) assert( p->a[i].anEq[j]>0 );
+  }
+
+  /* Update the anEq[] fields of any samples already collected. */
+  if( iChng<p->nMaxEqZero ){
+    for(i=p->nSample-1; i>=0; i--){
+      int j;
+      for(j=iChng; j<p->nCol; j++){
+        if( p->a[i].anEq[j]==0 ) p->a[i].anEq[j] = p->current.anEq[j];
+      }
     }
+    p->nMaxEqZero = iChng;
   }
 #endif