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Overview
Comment:Add the SQLITE_SCANSTAT_SELECTID metric. Use it to improve the ".stmtscan on" output in the shell.
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SHA1: 64ad5761a841f71530d41565b9fbe9d19c2d6aff
User & Date: drh 2014-11-06 04:42:20
Context
2014-11-06
12:08
Changes the formatting of ".scanstats on" in the shell so that the stats for subqueries are grouped together and occur after the main query. check-in: eacbbd88 user: drh tags: scanstatus
04:42
Add the SQLITE_SCANSTAT_SELECTID metric. Use it to improve the ".stmtscan on" output in the shell. check-in: 64ad5761 user: drh tags: scanstatus
03:55
Change the SQLITE_SCANSTAT_EST parameter so that it returns a double for the estimated number of output rows per loop, rather than a 64-bit integer. Revise the output format for the ".scanstats on" in the shell to make use of this new capability. check-in: f9684000 user: drh tags: scanstatus
Changes
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Changes to src/shell.c.

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*/
static void display_scanstats(
  sqlite3 *db,                    /* Database to query */
  ShellState *pArg                /* Pointer to ShellState */
){
#ifdef SQLITE_ENABLE_STMT_SCANSTATUS
  int i;

  double rEstLoop = 1.0;
  fprintf(pArg->out, "-------- scanstats --------\n");
  for(i=0; 1; i++){
    sqlite3_stmt *p = pArg->pStmt;
    sqlite3_int64 nLoop, nVisit;
    double rEst;

    const char *zExplain;
    if( sqlite3_stmt_scanstatus(p, i, SQLITE_SCANSTAT_NLOOP, (void*)&nLoop) ){
      break;
    }
    sqlite3_stmt_scanstatus(p, i, SQLITE_SCANSTAT_NVISIT, (void*)&nVisit);
    sqlite3_stmt_scanstatus(p, i, SQLITE_SCANSTAT_EST, (void*)&rEst);
    sqlite3_stmt_scanstatus(p, i, SQLITE_SCANSTAT_EXPLAIN, (void*)&zExplain);











    fprintf(pArg->out, "Loop %2d: \"%s\"\n", i, zExplain);
    rEstLoop *= rEst;
    fprintf(pArg->out, "        nLoop=%-8lld nRow=%-8lld estRow=%-8lld estRow/Loop=%-8g\n",
        nLoop, nVisit, (sqlite3_int64)rEstLoop, rEst
    );
  }

#else
  fprintf(pArg->out, "-------- scanstats --------\n");
  fprintf(pArg->out,
      "sqlite3_stmt_scanstatus() unavailable - "
      "rebuild with SQLITE_ENABLE_STMT_SCANSTATUS\n"
  );
#endif







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*/
static void display_scanstats(
  sqlite3 *db,                    /* Database to query */
  ShellState *pArg                /* Pointer to ShellState */
){
#ifdef SQLITE_ENABLE_STMT_SCANSTATUS
  int i;
  double *arEstLoop = 0;
  int nEstLoop = 0;
  fprintf(pArg->out, "-------- scanstats --------\n");
  for(i=0; 1; i++){
    sqlite3_stmt *p = pArg->pStmt;
    sqlite3_int64 nLoop, nVisit;
    double rEst, rLoop;
    int iSid;
    const char *zExplain;
    if( sqlite3_stmt_scanstatus(p, i, SQLITE_SCANSTAT_NLOOP, (void*)&nLoop) ){
      break;
    }
    sqlite3_stmt_scanstatus(p, i, SQLITE_SCANSTAT_NVISIT, (void*)&nVisit);
    sqlite3_stmt_scanstatus(p, i, SQLITE_SCANSTAT_EST, (void*)&rEst);
    sqlite3_stmt_scanstatus(p, i, SQLITE_SCANSTAT_EXPLAIN, (void*)&zExplain);
    sqlite3_stmt_scanstatus(p, i, SQLITE_SCANSTAT_SELECTID, (void*)&iSid);
    if( iSid>=nEstLoop ){
      arEstLoop = sqlite3_realloc(arEstLoop, sizeof(arEstLoop[0])*(iSid+1) );
      while( nEstLoop<=iSid ) arEstLoop[nEstLoop++] = 1.0; 
    }
    if( iSid>=0 ){
      arEstLoop[iSid] *= rEst;
      rLoop = arEstLoop[iSid];
    }else{
      rLoop = rEst;
    }
    fprintf(pArg->out, "Loop %2d: \"%s\"\n", i, zExplain);

    fprintf(pArg->out, "        nLoop=%-8lld nRow=%-8lld estRow=%-8lld estRow/Loop=%-8g\n",
        nLoop, nVisit, (sqlite3_int64)rLoop, rEst
    );
  }
  sqlite3_free(arEstLoop);
#else
  fprintf(pArg->out, "-------- scanstats --------\n");
  fprintf(pArg->out,
      "sqlite3_stmt_scanstatus() unavailable - "
      "rebuild with SQLITE_ENABLE_STMT_SCANSTATUS\n"
  );
#endif

Changes to src/sqlite.h.in.

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** total number of rows examined by all iterations of the X-th loop.</dd>
**
** [[SQLITE_SCANSTAT_EST]] <dt>SQLITE_SCANSTAT_EST</dt>
** <dd>^The "double" variable pointed to by the T parameter will be set to the
** query planner's estimate for the average number of rows output from each
** iteration of the X-th loop.  If the query planner's estimates was accurate,
** then this value will approximate the quotient NVISIT/NLOOP and the
** product of this value for the first N-1 loops will approximate
** the NLOOP value for the N-th loop.
**
** [[SQLITE_SCANSTAT_NAME]] <dt>SQLITE_SCANSTAT_NAME</dt>
** <dd>^The "const char *" variable pointed to by the T parameter will be set to 
** a zero-terminated UTF-8 string containing the name of the index or table used
** for the X-th loop.
**
** [[SQLITE_SCANSTAT_EXPLAIN]] <dt>SQLITE_SCANSTAT_EXPLAIN</dt>
** <dd>^The "const char *" variable pointed to by the T parameter will be set to 
** a zero-terminated UTF-8 string containing the [EXPLAIN QUERY PLAN] description
** for the X-th loop.







** </dl>
*/
#define SQLITE_SCANSTAT_NLOOP    0
#define SQLITE_SCANSTAT_NVISIT   1
#define SQLITE_SCANSTAT_EST      2
#define SQLITE_SCANSTAT_NAME     3
#define SQLITE_SCANSTAT_EXPLAIN  4


/*
** CAPI3REF: Prepared Statement Scan Status
**
** Return status data for a single loop within query pStmt.
**
** The "iScanStatusOp" parameter determines which status information to return.







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** total number of rows examined by all iterations of the X-th loop.</dd>
**
** [[SQLITE_SCANSTAT_EST]] <dt>SQLITE_SCANSTAT_EST</dt>
** <dd>^The "double" variable pointed to by the T parameter will be set to the
** query planner's estimate for the average number of rows output from each
** iteration of the X-th loop.  If the query planner's estimates was accurate,
** then this value will approximate the quotient NVISIT/NLOOP and the
** product of this value for all prior loops with the same SELECTID will
** be the NLOOP value for the current loop.
**
** [[SQLITE_SCANSTAT_NAME]] <dt>SQLITE_SCANSTAT_NAME</dt>
** <dd>^The "const char *" variable pointed to by the T parameter will be set to 
** a zero-terminated UTF-8 string containing the name of the index or table used
** for the X-th loop.
**
** [[SQLITE_SCANSTAT_EXPLAIN]] <dt>SQLITE_SCANSTAT_EXPLAIN</dt>
** <dd>^The "const char *" variable pointed to by the T parameter will be set to 
** a zero-terminated UTF-8 string containing the [EXPLAIN QUERY PLAN] description
** for the X-th loop.
**
** [[SQLITE_SCANSTAT_SELECTID]] <dt>SQLITE_SCANSTAT_SELECT</dt>
** <dd>^The "int" variable pointed to by the T parameter will be set to the
** "select-id" for the X-th loop.  The select-id identifies which query or
** subquery the loop is part of.  The main query has a select-id of zero.
** The select-id is the same value as is output in the first column
** of an [EXPLAIN QUERY PLAN] query.
** </dl>
*/
#define SQLITE_SCANSTAT_NLOOP    0
#define SQLITE_SCANSTAT_NVISIT   1
#define SQLITE_SCANSTAT_EST      2
#define SQLITE_SCANSTAT_NAME     3
#define SQLITE_SCANSTAT_EXPLAIN  4
#define SQLITE_SCANSTAT_SELECTID 5

/*
** CAPI3REF: Prepared Statement Scan Status
**
** Return status data for a single loop within query pStmt.
**
** The "iScanStatusOp" parameter determines which status information to return.

Changes to src/vdbeInt.h.

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typedef unsigned bft;  /* Bit Field Type */

typedef struct ScanStatus ScanStatus;
struct ScanStatus {
  int addrExplain;                /* OP_Explain for loop */
  int addrLoop;                   /* Address of "loops" counter */
  int addrVisit;                  /* Address of "rows visited" counter */

  LogEst nEst;                    /* Estimated output rows per loop */
  char *zName;                    /* Name of table or index */
};

/*
** An instance of the virtual machine.  This structure contains the complete
** state of the virtual machine.







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typedef unsigned bft;  /* Bit Field Type */

typedef struct ScanStatus ScanStatus;
struct ScanStatus {
  int addrExplain;                /* OP_Explain for loop */
  int addrLoop;                   /* Address of "loops" counter */
  int addrVisit;                  /* Address of "rows visited" counter */
  int iSelectID;                  /* The "Select-ID" for this loop */
  LogEst nEst;                    /* Estimated output rows per loop */
  char *zName;                    /* Name of table or index */
};

/*
** An instance of the virtual machine.  This structure contains the complete
** state of the virtual machine.

Changes to src/vdbeapi.c.

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    case SQLITE_SCANSTAT_EXPLAIN: {
      if( pScan->addrExplain ){
        *(const char**)pOut = p->aOp[ pScan->addrExplain ].p4.z;
      }else{
        *(const char**)pOut = 0;
      }
      break;








    }
    default: {
      return 1;
    }
  }
  return 0;
}







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    case SQLITE_SCANSTAT_EXPLAIN: {
      if( pScan->addrExplain ){
        *(const char**)pOut = p->aOp[ pScan->addrExplain ].p4.z;
      }else{
        *(const char**)pOut = 0;
      }
      break;
    }
    case SQLITE_SCANSTAT_SELECTID: {
      if( pScan->addrExplain ){
        *(int*)pOut = p->aOp[ pScan->addrExplain ].p1;
      }else{
        *(int*)pOut = -1;
      }
      break;
    }
    default: {
      return 1;
    }
  }
  return 0;
}