From 9d33d9e7ac064aed9de16d25544c7f45dcb76465 Mon Sep 17 00:00:00 2001
From: drh <drh@noemail.net>
Date: Tue, 10 Mar 2020 01:24:13 +0000
Subject: [PATCH] Background work for experiments trying to enhance ANALYZE so
 that it runs off of samples of the entire index and does not need to read the
 entire index.

patch reference:
https://www.sqlite.org/src/info/29d1cc5c3619a882

FossilOrigin-Name: 29d1cc5c3619a88229f18c3c8131228f8a2d151ac3d9203f0c7fc538a996ecec
---
 src/analyze.c | 90 ++++++++++++++++++++++++++++-----------------------
 1 file changed, 50 insertions(+), 40 deletions(-)

diff --git a/src/analyze.c b/src/analyze.c
index daf3af7..11ac430 100644
--- a/src/analyze.c
+++ b/src/analyze.c
@@ -188,6 +188,11 @@ static void openStatTable(
   Vdbe *v = sqlite3GetVdbe(pParse);
   int aRoot[ArraySize(aTable)];
   u8 aCreateTbl[ArraySize(aTable)];
+#ifdef SQLITE_ENABLE_STAT4
+  const int nToOpen = OptimizationEnabled(db,SQLITE_Stat4) ? 2 : 1;
+#else
+  const int nToOpen = 1;
+#endif
 
   if( v==0 ) return;
   assert( sqlite3BtreeHoldsAllMutexes(db) );
@@ -200,8 +205,9 @@ static void openStatTable(
   for(i=0; i<ArraySize(aTable); i++){
     const char *zTab = aTable[i].zName;
     Table *pStat;
+    aCreateTbl[i] = 0;
     if( (pStat = sqlite3FindTable(db, zTab, pDb->zDbSName))==0 ){
-      if( aTable[i].zCols ){
+      if( i<nToOpen ){
         /* The sqlite_statN table does not exist. Create it. Note that a 
         ** side-effect of the CREATE TABLE statement is to leave the rootpage 
         ** of the new table in register pParse->regRoot. This is important 
@@ -217,7 +223,6 @@ static void openStatTable(
       ** associated with the table zWhere. If zWhere is NULL, delete the
       ** entire contents of the table. */
       aRoot[i] = pStat->tnum;
-      aCreateTbl[i] = 0;
       sqlite3TableLock(pParse, iDb, aRoot[i], 1, zTab);
       if( zWhere ){
         sqlite3NestedParse(pParse,
@@ -236,7 +241,7 @@ static void openStatTable(
   }
 
   /* Open the sqlite_stat[134] tables for writing. */
-  for(i=0; aTable[i].zCols; i++){
+    for(i=0; i<nToOpen; i++){
     assert( i<ArraySize(aTable) );
     sqlite3VdbeAddOp4Int(v, OP_OpenWrite, iStatCur+i, aRoot[i], iDb, 3);
     sqlite3VdbeChangeP5(v, aCreateTbl[i]);
@@ -358,10 +363,12 @@ static void sampleCopy(StatAccum *p, StatSample *pTo, StatSample *pFrom){
   static void statAccumDestructor(void *pOld){
   StatAccum *p = (StatAccum*)pOld;
 #ifdef SQLITE_ENABLE_STAT4
-  int i;
-  for(i=0; i<p->nCol; i++) sampleClear(p->db, p->aBest+i);
-  for(i=0; i<p->mxSample; i++) sampleClear(p->db, p->a+i);
-  sampleClear(p->db, &p->current);
+    if( p->mxSample ){
+      int i;
+      for(i=0; i<p->nCol; i++) sampleClear(p->db, p->aBest+i);
+      for(i=0; i<p->mxSample; i++) sampleClear(p->db, p->a+i);
+      sampleClear(p->db, &p->current);
+    }
 #endif
   sqlite3DbFree(p->db, p);
 }
@@ -401,7 +408,7 @@ static void statInit(
   int n;                          /* Bytes of space to allocate */
   sqlite3 *db;                    /* Database connection */
 #ifdef SQLITE_ENABLE_STAT4
-  int mxSample = SQLITE_STAT4_SAMPLES;
+  int mxSample = sqlite3_value_int(argv[2]) ? SQLITE_STAT4_SAMPLES : 0;
 #endif
 
   /* Decode the three function arguments */
@@ -438,7 +445,7 @@ static void statInit(
   p->current.anEq = &p->current.anDLt[nColUp];
 
 #ifdef SQLITE_ENABLE_STAT4
-  {
+    if( mxSample ){
     u8 *pSpace;                     /* Allocated space not yet assigned */
     int i;                          /* Used to iterate through p->aSample[] */
 
@@ -705,7 +712,7 @@ static void statPush(
   }else{
     /* Second and subsequent calls get processed here */
 #ifdef SQLITE_ENABLE_STAT4
-    samplePushPrevious(p, iChng);
+    if( p->mxSample ) samplePushPrevious(p, iChng);
 #endif
     /* Update anDLt[], anLt[] and anEq[] to reflect the values that apply
     ** to the current row of the index. */
@@ -715,26 +722,22 @@ static void statPush(
     for(i=iChng; i<p->nCol; i++){
       p->current.anDLt[i]++;
 #ifdef SQLITE_ENABLE_STAT4
-      p->current.anLt[i] += p->current.anEq[i];
+    if( p->mxSample ) p->current.anLt[i] += p->current.anEq[i];
 #endif
       p->current.anEq[i] = 1;
     }
   }
   p->nRow++;
 #ifdef SQLITE_ENABLE_STAT4
-  if( sqlite3_value_type(argv[2])==SQLITE_INTEGER ){
-    sampleSetRowidInt64(p->db, &p->current, sqlite3_value_int64(argv[2]));
-  }else{
-    sampleSetRowid(p->db, &p->current, sqlite3_value_bytes(argv[2]),
-                                       sqlite3_value_blob(argv[2]));
-  }
-  p->current.iHash = p->iPrn = p->iPrn*1103515245 + 12345;
-#endif
-
-#ifdef SQLITE_ENABLE_STAT4
-  {
-    tRowcnt nLt = p->current.anLt[p->nCol-1];
-
+    if( p->mxSample ){
+	tRowcnt nLt;
+	if( sqlite3_value_type(argv[2])==SQLITE_INTEGER ){
+	   sampleSetRowidInt64(p->db, &p->current, sqlite3_value_int64(argv[2]));
+	   }else{
+		   sampleSetRowid(p->db, &p->current, sqlite3_value_bytes(argv[2]),sqlite3_value_blob(argv[2]));
+	   }
+	p->current.iHash = p->iPrn = p->iPrn*1103515245 + 12345;
+    nLt = p->current.anLt[p->nCol-1];
     /* Check if this is to be a periodic sample. If so, add it. */
     if( (nLt/p->nPSample)!=(nLt+1)/p->nPSample ){
       p->current.isPSample = 1;
@@ -804,6 +807,7 @@ static void statGet(
        || eCall==STAT_GET_ROWID || eCall==STAT_GET_NLT
        || eCall==STAT_GET_NDLT 
   );
+  assert( eCall==STAT_GET_STAT1 || p->mxSample );
   if( eCall==STAT_GET_STAT1 )
 #else
   assert( argc==1 );
@@ -1089,7 +1093,11 @@ static void analyzeOneTable(
     ** The third argument is only used for STAT4
     */
 #ifdef SQLITE_ENABLE_STAT4
-    sqlite3VdbeAddOp2(v, OP_Count, iIdxCur, regStat4+3);
+    if( OptimizationEnabled(db, SQLITE_Stat4) ){
+	sqlite3VdbeAddOp2(v, OP_Count, iIdxCur, regStat4+3);
+	}else{
+	  sqlite3VdbeAddOp2(v, OP_Integer, 0, regStat4+3);
+       }
 #endif
     sqlite3VdbeAddOp2(v, OP_Integer, nCol, regStat4+1);
     sqlite3VdbeAddOp2(v, OP_Integer, pIdx->nKeyCol, regStat4+2);
@@ -1171,21 +1179,23 @@ static void analyzeOneTable(
     **   if !eof(csr) goto next_row;
     */
 #ifdef SQLITE_ENABLE_STAT4
-    assert( regRowid==(regStat4+2) );
-    if( HasRowid(pTab) ){
-      sqlite3VdbeAddOp2(v, OP_IdxRowid, iIdxCur, regRowid);
-    }else{
-      Index *pPk = sqlite3PrimaryKeyIndex(pIdx->pTable);
-      int j, k, regKey;
-      regKey = sqlite3GetTempRange(pParse, pPk->nKeyCol);
-      for(j=0; j<pPk->nKeyCol; j++){
-        k = sqlite3TableColumnToIndex(pIdx, pPk->aiColumn[j]);
-        assert( k>=0 && k<pIdx->nColumn );
-        sqlite3VdbeAddOp3(v, OP_Column, iIdxCur, k, regKey+j);
-        VdbeComment((v, "%s", pTab->aCol[pPk->aiColumn[j]].zName));
+      if( OptimizationEnabled(db, SQLITE_Stat4) ){
+	 assert( regRowid==(regStat4+2) );
+	 if( HasRowid(pTab) ){
+            sqlite3VdbeAddOp2(v, OP_IdxRowid, iIdxCur, regRowid);
+	     }else{
+             Index *pPk = sqlite3PrimaryKeyIndex(pIdx->pTable);
+	     int j, k, regKey;
+	     regKey = sqlite3GetTempRange(pParse, pPk->nKeyCol);
+	     for(j=0; j<pPk->nKeyCol; j++){
+		 k = sqlite3TableColumnToIndex(pIdx, pPk->aiColumn[j]);
+		 assert( k>=0 && k<pIdx->nColumn );
+		 sqlite3VdbeAddOp3(v, OP_Column, iIdxCur, k, regKey+j);
+		 VdbeComment((v, "%s", pTab->aCol[pPk->aiColumn[j]].zName));
+	     }
+	     sqlite3VdbeAddOp3(v, OP_MakeRecord, regKey, pPk->nKeyCol, regRowid);
+	     sqlite3ReleaseTempRange(pParse, regKey, pPk->nKeyCol);
       }
-      sqlite3VdbeAddOp3(v, OP_MakeRecord, regKey, pPk->nKeyCol, regRowid);
-      sqlite3ReleaseTempRange(pParse, regKey, pPk->nKeyCol);
     }
 #endif
     assert( regChng==(regStat4+1) );
@@ -1206,7 +1216,7 @@ static void analyzeOneTable(
 
     /* Add the entries to the stat4 table. */
 #ifdef SQLITE_ENABLE_STAT4
-    {
+      if( OptimizationEnabled(db, SQLITE_Stat4) ){
       int regEq = regStat1;
       int regLt = regStat1+1;
       int regDLt = regStat1+2;
-- 
2.23.0