SQLite

** and indices.  These statistics are made available to the query planner
** to help it make better decisions about how to perform queries.
**
** The following system tables are or have been supported:
**
**    CREATE TABLE sqlite_stat1(tbl, idx, stat);
**    CREATE TABLE sqlite_stat2(tbl, idx, sampleno, sample);
**    CREATE TABLE sqlite_stat3(tbl, idx, nEq, nLt, nDLt, sample);
**
** Additional tables might be added in future releases of SQLite.
** The sqlite_stat2 table is not created or used unless the SQLite version
** is between 3.6.18 and 3.7.7, inclusive, and unless SQLite is compiled
** with SQLITE_ENABLE_STAT2.  The sqlite_stat2 table is deprecated.
** The sqlite_stat2 table is superceded by sqlite_stat3, which is only
** created and used by SQLite versions after 2011-08-09 with

** Format for sqlite_stat3:
**
** The sqlite_stat3 is an enhancement to sqlite_stat2.  A new name is
** used to avoid compatibility problems.  
**
** The format of the sqlite_stat3 table is similar to the format for
** the sqlite_stat2 table, with the following changes:  (1)
** The sampleno column is removed.  (2) Every sample has nEq, nLt, and nDLt
** columns which hold the approximate number of rows in the table that
** exactly match the sample, the approximate number of rows with values
** less than the sample, and the approximate number of distinct key values
** less than the sample, respectively.  (3) The number of samples can very 
** from one table to the next; the sample count does not have to be 
** exactly 10 as it is with sqlite_stat2.
**
** The ANALYZE command will typically generate sqlite_stat3 tables
** that contain between 10 and 40 samples which are distributed across
** the key space, though not uniformly, and which include samples with
** largest possible nEq values.
*/
#ifndef SQLITE_OMIT_ANALYZE

){
  static const struct {
    const char *zName;
    const char *zCols;
  } aTable[] = {
    { "sqlite_stat1", "tbl,idx,stat" },
#ifdef SQLITE_ENABLE_STAT3
    { "sqlite_stat3", "tbl,idx,neq,nlt,ndlt,sample" },
#endif
  };
  static const char *azToDrop[] = { 
    "sqlite_stat2",
#ifndef SQLITE_ENABLE_STAT3
    "sqlite_stat3",
#endif

  }
}

/*
** Recommended number of samples for sqlite_stat3
*/
#ifndef SQLITE_STAT3_SAMPLES
# define SQLITE_STAT3_SAMPLES 24
#endif

/*
** Three SQL functions - stat3_init(), stat3_push(), and stat3_pop() -
** share an instance of the following structure to hold their state
** information.
*/
typedef struct Stat3Accum Stat3Accum;
struct Stat3Accum {
  tRowcnt nRow;             /* Number of rows in the entire table */
  tRowcnt nPSample;         /* How often to do a periodic sample */
  int iMin;                 /* Index of entry with minimum nEq and hash */
  int mxSample;             /* Maximum number of samples to accumulate */
  int nSample;              /* Current number of samples */
  u32 iPrn;                 /* Pseudo-random number used for sampling */
  struct Stat3Sample {
    i64 iRowid;                /* Rowid in main table of the key */
    tRowcnt nEq;               /* sqlite_stat3.nEq */
    tRowcnt nLt;               /* sqlite_stat3.nLt */
    tRowcnt nDLt;              /* sqlite_stat3.nDLt */
    u8 isPSample;              /* True if a periodic sample */
    u32 iHash;                 /* Tiebreaker hash */
  } *a;                     /* An array of samples */
};

#ifdef SQLITE_ENABLE_STAT3
/*

    sqlite3_result_error_nomem(context);
    return;
  }
  memset(p, 0, n);
  p->a = (struct Stat3Sample*)&p[1];
  p->nRow = nRow;
  p->mxSample = mxSample;
  p->nPSample = p->nRow/(mxSample/3+1) + 1;
  sqlite3_randomness(sizeof(p->iPrn), &p->iPrn);
  sqlite3_result_blob(context, p, sizeof(p), sqlite3_free);
}
static const FuncDef stat3InitFuncdef = {
  2,                /* nArg */
  SQLITE_UTF8,      /* iPrefEnc */
  0,                /* flags */
  0,                /* pUserData */
  0,                /* pNext */
  stat3Init,        /* xFunc */
  0,                /* xStep */
  0,                /* xFinalize */
  "stat3_init",     /* zName */
  0,                /* pHash */
  0                 /* pDestructor */
};


/*
** Implementation of the stat3_push(nEq,nLt,nDLt,rowid,P) SQL function.  The
** arguments describe a single key instance.  This routine makes the 
** decision about whether or not to retain this key for the sqlite_stat3
** table.
**
** The return value is NULL.
*/
static void stat3Push(
  sqlite3_context *context,
  int argc,
  sqlite3_value **argv
){
  Stat3Accum *p = (Stat3Accum*)sqlite3_value_blob(argv[4]);
  tRowcnt nEq = sqlite3_value_int64(argv[0]);
  tRowcnt nLt = sqlite3_value_int64(argv[1]);
  tRowcnt nDLt = sqlite3_value_int64(argv[2]);
  i64 rowid = sqlite3_value_int64(argv[3]);
  u8 isPSample = 0;
  u8 doInsert = 0;
  int iMin = p->iMin;
  struct Stat3Sample *pSample;
  int i;
  u32 h;
  if( nEq==0 ) return;





  h = p->iPrn = p->iPrn*1103515245 + 12345;
  if( (nLt/p->nPSample)!=((nEq+nLt)/p->nPSample) ){
    doInsert = isPSample = 1;
  }else if( p->nSample<p->mxSample ){
    doInsert = 1;
  }else{
    if( nEq>p->a[iMin].nEq || (nEq==p->a[iMin].nEq && h>p->a[iMin].iHash) ){
      doInsert = 1;
    }
  }
  if( !doInsert ) return;
  if( p->nSample==p->mxSample ){
    if( iMin<p->nSample ){
      memcpy(&p->a[iMin], &p->a[iMin+1], sizeof(p->a[0])*(p->nSample-iMin));
    }
    pSample = &p->a[p->nSample-1];
  }else{
    pSample = &p->a[p->nSample++];
  }
  pSample->iRowid = rowid;
  pSample->nEq = nEq;
  pSample->nLt = nLt;
  pSample->nDLt = nDLt;
  pSample->iHash = h;
  pSample->isPSample = isPSample;

  /* Find the new minimum */
  if( p->nSample==p->mxSample ){
    pSample = p->a;
    i = 0;

        h = pSample->iHash;
      }
    }
    p->iMin = iMin;
  }
}
static const FuncDef stat3PushFuncdef = {
  5,                /* nArg */
  SQLITE_UTF8,      /* iPrefEnc */
  0,                /* flags */
  0,                /* pUserData */
  0,                /* pNext */
  stat3Push,        /* xFunc */
  0,                /* xStep */
  0,                /* xFinalize */

** used to query the results.  Content is returned for the Nth sqlite_stat3
** row where N is between 0 and S-1 and S is the number of samples.  The
** value returned depends on the number of arguments.
**
**   argc==2    result:  rowid
**   argc==3    result:  nEq
**   argc==4    result:  nLt
**   argc==5    result:  nDLt
*/
static void stat3Get(
  sqlite3_context *context,
  int argc,
  sqlite3_value **argv
){
  int n = sqlite3_value_int(argv[1]);
  Stat3Accum *p = (Stat3Accum*)sqlite3_value_blob(argv[0]);

  assert( p!=0 );
  if( p->nSample<=n ) return;
  switch( argc ){
    case 2: sqlite3_result_int64(context, p->a[n].iRowid); break;
    case 3: sqlite3_result_int64(context, p->a[n].nEq);    break;
    case 4: sqlite3_result_int64(context, p->a[n].nLt);    break;
    case 5: sqlite3_result_int64(context, p->a[n].nDLt);   break;
  }
}
static const FuncDef stat3GetFuncdef = {
  -1,               /* nArg */
  SQLITE_UTF8,      /* iPrefEnc */
  0,                /* flags */
  0,                /* pUserData */

  int iDb;                     /* Index of database containing pTab */
  int regTabname = iMem++;     /* Register containing table name */
  int regIdxname = iMem++;     /* Register containing index name */
  int regStat1 = iMem++;       /* The stat column of sqlite_stat1 */
#ifdef SQLITE_ENABLE_STAT3
  int regNumEq = regStat1;     /* Number of instances.  Same as regStat1 */
  int regNumLt = iMem++;       /* Number of keys less than regSample */
  int regNumDLt = iMem++;      /* Number of distinct keys less than regSample */
  int regSample = iMem++;      /* The next sample value */
  int regRowid = regSample;    /* Rowid of a sample */
  int regAccum = iMem++;       /* Register to hold Stat3Accum object */
  int regLoop = iMem++;        /* Loop counter */
  int regCount = iMem++;       /* Number of rows in the table or index */
  int regTemp1 = iMem++;       /* Intermediate register */
  int regTemp2 = iMem++;       /* Intermediate register */

      once = 0;
      sqlite3OpenTable(pParse, iTabCur, iDb, pTab, OP_OpenRead);
    }
    sqlite3VdbeAddOp2(v, OP_Count, iIdxCur, regCount);
    sqlite3VdbeAddOp2(v, OP_Integer, SQLITE_STAT3_SAMPLES, regTemp1);
    sqlite3VdbeAddOp2(v, OP_Integer, 0, regNumEq);
    sqlite3VdbeAddOp2(v, OP_Integer, 0, regNumLt);
    sqlite3VdbeAddOp2(v, OP_Integer, -1, regNumDLt);
    sqlite3VdbeAddOp4(v, OP_Function, 1, regCount, regAccum,
                      (char*)&stat3InitFuncdef, P4_FUNCDEF);
    sqlite3VdbeChangeP5(v, 2);
#endif /* SQLITE_ENABLE_STAT3 */

    /* The block of memory cells initialized here is used as follows.
    **

    for(i=0; i<nCol; i++){
      sqlite3VdbeJumpHere(v, aChngAddr[i]);  /* Set jump dest for the OP_Ne */
      if( i==0 ){
        sqlite3VdbeJumpHere(v, addrIfNot);   /* Jump dest for OP_IfNot */
#ifdef SQLITE_ENABLE_STAT3
        sqlite3VdbeAddOp4(v, OP_Function, 1, regNumEq, regTemp2,
                          (char*)&stat3PushFuncdef, P4_FUNCDEF);
        sqlite3VdbeChangeP5(v, 5);
        sqlite3VdbeAddOp3(v, OP_Column, iIdxCur, pIdx->nColumn, regRowid);
        sqlite3VdbeAddOp3(v, OP_Add, regNumEq, regNumLt, regNumLt);
        sqlite3VdbeAddOp2(v, OP_AddImm, regNumDLt, 1);
        sqlite3VdbeAddOp2(v, OP_Integer, 1, regNumEq);
#endif        
      }
      sqlite3VdbeAddOp2(v, OP_AddImm, iMem+i+1, 1);
      sqlite3VdbeAddOp3(v, OP_Column, iIdxCur, i, iMem+nCol+i+1);
    }
    sqlite3DbFree(db, aChngAddr);

    /* Always jump here after updating the iMem+1...iMem+1+nCol counters */
    sqlite3VdbeResolveLabel(v, endOfLoop);

    sqlite3VdbeAddOp2(v, OP_Next, iIdxCur, topOfLoop);
    sqlite3VdbeAddOp1(v, OP_Close, iIdxCur);
#ifdef SQLITE_ENABLE_STAT3
    sqlite3VdbeAddOp4(v, OP_Function, 1, regNumEq, regTemp2,
                      (char*)&stat3PushFuncdef, P4_FUNCDEF);
    sqlite3VdbeChangeP5(v, 5);
    sqlite3VdbeAddOp2(v, OP_Integer, -1, regLoop);
    shortJump = 
    sqlite3VdbeAddOp2(v, OP_AddImm, regLoop, 1);
    sqlite3VdbeAddOp4(v, OP_Function, 1, regAccum, regTemp1,
                      (char*)&stat3GetFuncdef, P4_FUNCDEF);
    sqlite3VdbeChangeP5(v, 2);
    sqlite3VdbeAddOp1(v, OP_IsNull, regTemp1);
    sqlite3VdbeAddOp3(v, OP_NotExists, iTabCur, shortJump, regTemp1);
    sqlite3VdbeAddOp3(v, OP_Column, iTabCur, pIdx->aiColumn[0], regSample);
    sqlite3ColumnDefault(v, pTab, pIdx->aiColumn[0], regSample);
    sqlite3VdbeAddOp4(v, OP_Function, 1, regAccum, regNumEq,
                      (char*)&stat3GetFuncdef, P4_FUNCDEF);
    sqlite3VdbeChangeP5(v, 3);
    sqlite3VdbeAddOp4(v, OP_Function, 1, regAccum, regNumLt,
                      (char*)&stat3GetFuncdef, P4_FUNCDEF);
    sqlite3VdbeChangeP5(v, 4);
    sqlite3VdbeAddOp4(v, OP_Function, 1, regAccum, regNumDLt,
                      (char*)&stat3GetFuncdef, P4_FUNCDEF);
    sqlite3VdbeChangeP5(v, 5);
    sqlite3VdbeAddOp4(v, OP_MakeRecord, regTabname, 6, regRec, "bbbbbb", 0);
    sqlite3VdbeAddOp2(v, OP_NewRowid, iStatCur+1, regNewRowid);
    sqlite3VdbeAddOp3(v, OP_Insert, iStatCur+1, regRec, regNewRowid);
    sqlite3VdbeAddOp2(v, OP_Goto, 0, shortJump);
    sqlite3VdbeJumpHere(v, shortJump+2);
#endif        

    /* Store the results in sqlite_stat1.

      sqlite3_finalize(pStmt);
      return SQLITE_NOMEM;
    }
  }
  sqlite3_finalize(pStmt);

  zSql = sqlite3MPrintf(db, 
      "SELECT idx,nlt,neq,sample FROM %Q.sqlite_stat3", zDb);

  if( !zSql ){
    return SQLITE_NOMEM;
  }
  rc = sqlite3_prepare(db, zSql, -1, &pStmt, 0);
  sqlite3DbFree(db, zSql);
  if( rc ) return rc;