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Overview
Comment:Add an option to generate stat1 data based on a subset of the user database table contents to sqlite3_expert.
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SHA3-256:c69c3e21db6e141f7e24226c6432f2ed31fe5f177bd23781915871f8600ee56a
User & Date: dan 2017-04-20 09:54:04
Context
2017-04-20
16:18
Avoid adding INTEGER PRIMARY KEY columns to candidate indexes. check-in: 4577fea5 user: dan tags: schemalint
16:08
Avoid creating a temp table in the user database in the sqlite3_expert code. Trouble is, this makes sampling for stat1 data much slower. check-in: c62e3582 user: dan tags: schemalint-failure
09:54
Add an option to generate stat1 data based on a subset of the user database table contents to sqlite3_expert. check-in: c69c3e21 user: dan tags: schemalint
2017-04-18
20:10
Have sqlite3_expert_analyze() populate the sqlite_stat1 table before running queries through the planner for the second time. check-in: a157fcfd user: dan tags: schemalint
Changes
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Changes to ext/expert/expert.c.

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  fprintf(stderr, "\n");
  fprintf(stderr, "Usage %s ?OPTIONS? DATABASE\n", argv[0]);
  fprintf(stderr, "\n");
  fprintf(stderr, "Options are:\n");
  fprintf(stderr, "  -sql SQL   (analyze SQL statements passed as argument)\n");
  fprintf(stderr, "  -file FILE (read SQL statements from file FILE)\n");
  fprintf(stderr, "  -verbose LEVEL (integer verbosity level. default 1)\n");

  exit(-1);
}

static int readSqlFromFile(sqlite3expert *p, const char *zFile, char **pzErr){
  FILE *in = fopen(zFile, "rb");
  long nIn;
  size_t nRead;
................................................................................
      char *zArg = argv[i];
      int nArg = strlen(zArg);
      if( nArg>=2 && 0==sqlite3_strnicmp(zArg, "-file", nArg) ){
        if( ++i==(argc-1) ) option_requires_argument("-file");
        rc = readSqlFromFile(p, argv[i], &zErr);
      }

      else if( nArg>=2 && 0==sqlite3_strnicmp(zArg, "-sql", nArg) ){
        if( ++i==(argc-1) ) option_requires_argument("-sql");
        rc = sqlite3_expert_sql(p, argv[i], &zErr);
      }








      else if( nArg>=2 && 0==sqlite3_strnicmp(zArg, "-verbose", nArg) ){
        if( ++i==(argc-1) ) option_requires_argument("-verbose");
        iVerbose = option_integer_arg(argv[i]);
      }

      else{







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  fprintf(stderr, "\n");
  fprintf(stderr, "Usage %s ?OPTIONS? DATABASE\n", argv[0]);
  fprintf(stderr, "\n");
  fprintf(stderr, "Options are:\n");
  fprintf(stderr, "  -sql SQL   (analyze SQL statements passed as argument)\n");
  fprintf(stderr, "  -file FILE (read SQL statements from file FILE)\n");
  fprintf(stderr, "  -verbose LEVEL (integer verbosity level. default 1)\n");
  fprintf(stderr, "  -sample PERCENT (percent of db to sample. default 100)\n");
  exit(-1);
}

static int readSqlFromFile(sqlite3expert *p, const char *zFile, char **pzErr){
  FILE *in = fopen(zFile, "rb");
  long nIn;
  size_t nRead;
................................................................................
      char *zArg = argv[i];
      int nArg = strlen(zArg);
      if( nArg>=2 && 0==sqlite3_strnicmp(zArg, "-file", nArg) ){
        if( ++i==(argc-1) ) option_requires_argument("-file");
        rc = readSqlFromFile(p, argv[i], &zErr);
      }

      else if( nArg>=3 && 0==sqlite3_strnicmp(zArg, "-sql", nArg) ){
        if( ++i==(argc-1) ) option_requires_argument("-sql");
        rc = sqlite3_expert_sql(p, argv[i], &zErr);
      }

      else if( nArg>=3 && 0==sqlite3_strnicmp(zArg, "-sample", nArg) ){
        int iSample;
        if( ++i==(argc-1) ) option_requires_argument("-sample");
        iSample = option_integer_arg(argv[i]);
        sqlite3_expert_config(p, EXPERT_CONFIG_SAMPLE, iSample);
      }

      else if( nArg>=2 && 0==sqlite3_strnicmp(zArg, "-verbose", nArg) ){
        if( ++i==(argc-1) ) option_requires_argument("-verbose");
        iVerbose = option_integer_arg(argv[i]);
      }

      else{

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typedef struct IdxColumn IdxColumn;
typedef struct IdxConstraint IdxConstraint;
typedef struct IdxScan IdxScan;
typedef struct IdxStatement IdxStatement;
typedef struct IdxTable IdxTable;
typedef struct IdxWrite IdxWrite;




/*
** A single constraint. Equivalent to either "col = ?" or "col < ?" (or
** any other type of single-ended range constraint on a column).
**
** pLink:
**   Used to temporarily link IdxConstraint objects into lists while
................................................................................
  IdxHashEntry *aHash[IDX_HASH_SIZE];
};

/*
** sqlite3expert object.
*/
struct sqlite3expert {

  sqlite3 *db;                    /* User database */
  sqlite3 *dbm;                   /* In-memory db for this analysis */
  sqlite3 *dbv;                   /* Vtab schema for this analysis */
  IdxTable *pTable;               /* List of all IdxTable objects */
  IdxScan *pScan;                 /* List of scan objects */
  IdxWrite *pWrite;               /* List of write objects */
  IdxStatement *pStatement;       /* List of IdxStatement objects */
................................................................................
}

static int idxProcessOneTrigger(
  sqlite3expert *p, 
  IdxWrite *pWrite, 
  char **pzErr
){
  static const char *zInt = "t592690916721053953805701627921227776";
  static const char *zDrop = "DROP TABLE t592690916721053953805701627921227776";
  IdxTable *pTab = pWrite->pTab;
  const char *zTab = pTab->zName;
  const char *zSql = 
    "SELECT 'CREATE TEMP' || substr(sql, 7) FROM sqlite_master "
    "WHERE tbl_name = %Q AND type IN ('table', 'trigger') "
    "ORDER BY type;";
  sqlite3_stmt *pSelect = 0;
................................................................................
        sqlite3_free(zOuter);
      }
    }
  }
  idxFinalize(&rc, pSchema);
  return rc;
}

































struct IdxRemCtx {
  int nSlot;
  struct IdxRemSlot {
    int eType;                    /* SQLITE_NULL, INTEGER, REAL, TEXT, BLOB */
    i64 iVal;                     /* SQLITE_INTEGER value */
    double rVal;                  /* SQLITE_FLOAT value */
................................................................................
  char *zOrder = 0;
  char *zQuery = 0;
  int nCol = 0;
  int i;
  sqlite3_stmt *pQuery = 0;
  int *aStat = 0;
  int rc = SQLITE_OK;



  /* Formulate the query text */
  sqlite3_bind_text(pIndexXInfo, 1, zIdx, -1, SQLITE_STATIC);
  while( SQLITE_OK==rc && SQLITE_ROW==sqlite3_step(pIndexXInfo) ){
    const char *zComma = zCols==0 ? "" : ", ";
    const char *zName = (const char*)sqlite3_column_text(pIndexXInfo, 0);
    const char *zColl = (const char*)sqlite3_column_text(pIndexXInfo, 1);
    zCols = idxAppendText(&rc, zCols, 
        "%sx.%Q IS rem(%d, x.%Q) COLLATE %s", zComma, zName, nCol, zName, zColl
    );
    zOrder = idxAppendText(&rc, zOrder, "%s%d", zComma, ++nCol);
  }
  if( rc==SQLITE_OK ){

    zQuery = sqlite3_mprintf(
        "SELECT %s FROM %Q x ORDER BY %s", zCols, zTab, zOrder
    );





  }
  sqlite3_free(zCols);
  sqlite3_free(zOrder);

  /* Formulate the query text */
  if( rc==SQLITE_OK ){
    rc = idxPrepareStmt(p->db, &pQuery, pzErr, zQuery);
................................................................................
    }
  }
  sqlite3_free(aStat);
  idxFinalize(&rc, pQuery);

  return rc;
}




















/*
** This function is called as part of sqlite3_expert_analyze(). Candidate
** indexes have already been created in database sqlite3expert.dbm, this
** function populates sqlite_stat1 table in the same database.
**
** The stat1 data is generated by querying the 
*/
static int idxPopulateStat1(sqlite3expert *p, char **pzErr){
  int rc = SQLITE_OK;
  int nMax =0;
  struct IdxRemCtx *pCtx = 0;

  int i;

  sqlite3_stmt *pAllIndex = 0;
  sqlite3_stmt *pIndexXInfo = 0;
  sqlite3_stmt *pWrite = 0;

  const char *zAllIndex = 
    "SELECT s.name, l.name FROM "
    "  sqlite_master AS s, "
    "  pragma_index_list(s.name) AS l "
    "WHERE s.type = 'table'";
  const char *zIndexXInfo = 
    "SELECT name, coll FROM pragma_index_xinfo(?) WHERE key";
  const char *zWrite = "INSERT INTO sqlite_stat1 VALUES(?, ?, ?)";




  rc = idxLargestIndex(p->dbm, &nMax, pzErr);
  if( nMax<=0 || rc!=SQLITE_OK ) return rc;

  rc = sqlite3_exec(p->dbm, "ANALYZE; PRAGMA writable_schema=1", 0, 0, 0);

  if( rc==SQLITE_OK ){
................................................................................
  }

  if( rc==SQLITE_OK ){
    rc = sqlite3_create_function(
        p->db, "rem", 2, SQLITE_UTF8, (void*)pCtx, idxRemFunc, 0, 0
    );
  }






  if( rc==SQLITE_OK ){
    pCtx->nSlot = nMax+1;
    rc = idxPrepareStmt(p->dbm, &pAllIndex, pzErr, zAllIndex);
  }
  if( rc==SQLITE_OK ){
    rc = idxPrepareStmt(p->dbm, &pIndexXInfo, pzErr, zIndexXInfo);
  }
  if( rc==SQLITE_OK ){
    rc = idxPrepareStmt(p->dbm, &pWrite, pzErr, zWrite);
  }

  while( rc==SQLITE_OK && SQLITE_ROW==sqlite3_step(pAllIndex) ){

    const char *zTab = (const char*)sqlite3_column_text(pAllIndex, 0);
    const char *zIdx = (const char*)sqlite3_column_text(pAllIndex, 1);








    rc = idxPopulateOneStat1(p, pIndexXInfo, pWrite, zTab, zIdx, pzErr);






  }

  idxFinalize(&rc, pAllIndex);
  idxFinalize(&rc, pIndexXInfo);
  idxFinalize(&rc, pWrite);

  for(i=0; i<pCtx->nSlot; i++){
................................................................................
    sqlite3_free(pCtx->aSlot[i].z);
  }
  sqlite3_free(pCtx);

  if( rc==SQLITE_OK ){
    rc = sqlite3_exec(p->dbm, "ANALYZE sqlite_master", 0, 0, 0);
  }


  return rc;
}

/*
** Allocate a new sqlite3expert object.
*/
sqlite3expert *sqlite3_expert_new(sqlite3 *db, char **pzErrmsg){
................................................................................
  ** will contain a virtual table corresponding to each real table in
  ** the user database schema, and a copy of each view. It is used to
  ** collect information regarding the WHERE, ORDER BY and other clauses
  ** of the user's query.
  */
  if( rc==SQLITE_OK ){
    pNew->db = db;

    rc = sqlite3_open(":memory:", &pNew->dbv);
  }
  if( rc==SQLITE_OK ){
    rc = sqlite3_open(":memory:", &pNew->dbm);
    if( rc==SQLITE_OK ){
      sqlite3_db_config(pNew->dbm, SQLITE_DBCONFIG_FULL_EQP, 1, (int*)0);
    }
................................................................................
  ** return the new sqlite3expert handle.  */
  if( rc!=SQLITE_OK ){
    sqlite3_expert_destroy(pNew);
    pNew = 0;
  }
  return pNew;
}

























/*
** Add an SQL statement to the analysis.
*/
int sqlite3_expert_sql(
  sqlite3expert *p,               /* From sqlite3_expert_new() */
  const char *zSql,               /* SQL statement to add */







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typedef struct IdxColumn IdxColumn;
typedef struct IdxConstraint IdxConstraint;
typedef struct IdxScan IdxScan;
typedef struct IdxStatement IdxStatement;
typedef struct IdxTable IdxTable;
typedef struct IdxWrite IdxWrite;

#define UNIQUE_TABLE_NAME "t592690916721053953805701627921227776"


/*
** A single constraint. Equivalent to either "col = ?" or "col < ?" (or
** any other type of single-ended range constraint on a column).
**
** pLink:
**   Used to temporarily link IdxConstraint objects into lists while
................................................................................
  IdxHashEntry *aHash[IDX_HASH_SIZE];
};

/*
** sqlite3expert object.
*/
struct sqlite3expert {
  int iSample;                    /* Percentage of tables to sample for stat1 */
  sqlite3 *db;                    /* User database */
  sqlite3 *dbm;                   /* In-memory db for this analysis */
  sqlite3 *dbv;                   /* Vtab schema for this analysis */
  IdxTable *pTable;               /* List of all IdxTable objects */
  IdxScan *pScan;                 /* List of scan objects */
  IdxWrite *pWrite;               /* List of write objects */
  IdxStatement *pStatement;       /* List of IdxStatement objects */
................................................................................
}

static int idxProcessOneTrigger(
  sqlite3expert *p, 
  IdxWrite *pWrite, 
  char **pzErr
){
  static const char *zInt = UNIQUE_TABLE_NAME;
  static const char *zDrop = "DROP TABLE " UNIQUE_TABLE_NAME;
  IdxTable *pTab = pWrite->pTab;
  const char *zTab = pTab->zName;
  const char *zSql = 
    "SELECT 'CREATE TEMP' || substr(sql, 7) FROM sqlite_master "
    "WHERE tbl_name = %Q AND type IN ('table', 'trigger') "
    "ORDER BY type;";
  sqlite3_stmt *pSelect = 0;
................................................................................
        sqlite3_free(zOuter);
      }
    }
  }
  idxFinalize(&rc, pSchema);
  return rc;
}

struct IdxSampleCtx {
  int iTarget;
  double target;                  /* Target nRet/nRow value */
  double nRow;                    /* Number of rows seen */
  double nRet;                    /* Number of rows returned */
};

static void idxSampleFunc(
  sqlite3_context *pCtx,
  int argc,
  sqlite3_value **argv
){
  struct IdxSampleCtx *p = (struct IdxSampleCtx*)sqlite3_user_data(pCtx);
  int bRet;

  assert( argc==0 );
  if( p->nRow==0.0 ){
    bRet = 1;
  }else{
    bRet = (p->nRet / p->nRow) <= p->target;
    if( bRet==0 ){
      unsigned short rnd;
      sqlite3_randomness(2, (void*)&rnd);
      bRet = ((int)rnd % 100) <= p->iTarget;
    }
  }

  sqlite3_result_int(pCtx, bRet);
  p->nRow += 1.0;
  p->nRet += (double)bRet;
}

struct IdxRemCtx {
  int nSlot;
  struct IdxRemSlot {
    int eType;                    /* SQLITE_NULL, INTEGER, REAL, TEXT, BLOB */
    i64 iVal;                     /* SQLITE_INTEGER value */
    double rVal;                  /* SQLITE_FLOAT value */
................................................................................
  char *zOrder = 0;
  char *zQuery = 0;
  int nCol = 0;
  int i;
  sqlite3_stmt *pQuery = 0;
  int *aStat = 0;
  int rc = SQLITE_OK;

  assert( p->iSample>0 );

  /* Formulate the query text */
  sqlite3_bind_text(pIndexXInfo, 1, zIdx, -1, SQLITE_STATIC);
  while( SQLITE_OK==rc && SQLITE_ROW==sqlite3_step(pIndexXInfo) ){
    const char *zComma = zCols==0 ? "" : ", ";
    const char *zName = (const char*)sqlite3_column_text(pIndexXInfo, 0);
    const char *zColl = (const char*)sqlite3_column_text(pIndexXInfo, 1);
    zCols = idxAppendText(&rc, zCols, 
        "%sx.%Q IS rem(%d, x.%Q) COLLATE %s", zComma, zName, nCol, zName, zColl
    );
    zOrder = idxAppendText(&rc, zOrder, "%s%d", zComma, ++nCol);
  }
  if( rc==SQLITE_OK ){
    if( p->iSample==100 ){
      zQuery = sqlite3_mprintf(
          "SELECT %s FROM %Q x ORDER BY %s", zCols, zTab, zOrder
      );
    }else{
      zQuery = sqlite3_mprintf(
          "SELECT %s FROM temp."UNIQUE_TABLE_NAME" x ORDER BY %s", zCols, zOrder
      );
    }
  }
  sqlite3_free(zCols);
  sqlite3_free(zOrder);

  /* Formulate the query text */
  if( rc==SQLITE_OK ){
    rc = idxPrepareStmt(p->db, &pQuery, pzErr, zQuery);
................................................................................
    }
  }
  sqlite3_free(aStat);
  idxFinalize(&rc, pQuery);

  return rc;
}

static int idxBuildSampleTable(sqlite3expert *p, const char *zTab){
  int rc;
  char *zSql;

  rc = sqlite3_exec(p->db, "DROP TABLE IF EXISTS temp."UNIQUE_TABLE_NAME,0,0,0);
  if( rc!=SQLITE_OK ) return rc;

  zSql = sqlite3_mprintf(
      "CREATE TABLE temp." UNIQUE_TABLE_NAME 
      "  AS SELECT * FROM %Q WHERE sample()"
      , zTab
  );
  if( zSql==0 ) return SQLITE_NOMEM;
  rc = sqlite3_exec(p->db, zSql, 0, 0, 0);
  sqlite3_free(zSql);

  return rc;
}

/*
** This function is called as part of sqlite3_expert_analyze(). Candidate
** indexes have already been created in database sqlite3expert.dbm, this
** function populates sqlite_stat1 table in the same database.
**
** The stat1 data is generated by querying the 
*/
static int idxPopulateStat1(sqlite3expert *p, char **pzErr){
  int rc = SQLITE_OK;
  int nMax =0;
  struct IdxRemCtx *pCtx = 0;
  struct IdxSampleCtx samplectx; 
  int i;
  i64 iPrev = -100000;
  sqlite3_stmt *pAllIndex = 0;
  sqlite3_stmt *pIndexXInfo = 0;
  sqlite3_stmt *pWrite = 0;

  const char *zAllIndex =
    "SELECT s.rowid, s.name, l.name FROM "
    "  sqlite_master AS s, "
    "  pragma_index_list(s.name) AS l "
    "WHERE s.type = 'table'";
  const char *zIndexXInfo = 
    "SELECT name, coll FROM pragma_index_xinfo(?) WHERE key";
  const char *zWrite = "INSERT INTO sqlite_stat1 VALUES(?, ?, ?)";

  /* If iSample==0, no sqlite_stat1 data is required. */
  if( p->iSample==0 ) return SQLITE_OK;

  rc = idxLargestIndex(p->dbm, &nMax, pzErr);
  if( nMax<=0 || rc!=SQLITE_OK ) return rc;

  rc = sqlite3_exec(p->dbm, "ANALYZE; PRAGMA writable_schema=1", 0, 0, 0);

  if( rc==SQLITE_OK ){
................................................................................
  }

  if( rc==SQLITE_OK ){
    rc = sqlite3_create_function(
        p->db, "rem", 2, SQLITE_UTF8, (void*)pCtx, idxRemFunc, 0, 0
    );
  }
  if( rc==SQLITE_OK ){
    rc = sqlite3_create_function(
        p->db, "sample", 0, SQLITE_UTF8, (void*)&samplectx, idxSampleFunc, 0, 0
    );
  }

  if( rc==SQLITE_OK ){
    pCtx->nSlot = nMax+1;
    rc = idxPrepareStmt(p->dbm, &pAllIndex, pzErr, zAllIndex);
  }
  if( rc==SQLITE_OK ){
    rc = idxPrepareStmt(p->dbm, &pIndexXInfo, pzErr, zIndexXInfo);
  }
  if( rc==SQLITE_OK ){
    rc = idxPrepareStmt(p->dbm, &pWrite, pzErr, zWrite);
  }

  while( rc==SQLITE_OK && SQLITE_ROW==sqlite3_step(pAllIndex) ){
    i64 iRowid = sqlite3_column_int64(pAllIndex, 0);
    const char *zTab = (const char*)sqlite3_column_text(pAllIndex, 1);
    const char *zIdx = (const char*)sqlite3_column_text(pAllIndex, 2);
    if( p->iSample<100 && iPrev!=iRowid ){
      samplectx.target = (double)p->iSample / 100.0;
      samplectx.iTarget = p->iSample;
      samplectx.nRow = 0.0;
      samplectx.nRet = 0.0;
      rc = idxBuildSampleTable(p, zTab);
      if( rc!=SQLITE_OK ) break;
    }
    rc = idxPopulateOneStat1(p, pIndexXInfo, pWrite, zTab, zIdx, pzErr);
    iPrev = iRowid;
  }
  if( p->iSample<100 ){
    rc = sqlite3_exec(p->db, "DROP TABLE IF EXISTS temp." UNIQUE_TABLE_NAME,
        0,0,0
    );
  }

  idxFinalize(&rc, pAllIndex);
  idxFinalize(&rc, pIndexXInfo);
  idxFinalize(&rc, pWrite);

  for(i=0; i<pCtx->nSlot; i++){
................................................................................
    sqlite3_free(pCtx->aSlot[i].z);
  }
  sqlite3_free(pCtx);

  if( rc==SQLITE_OK ){
    rc = sqlite3_exec(p->dbm, "ANALYZE sqlite_master", 0, 0, 0);
  }

  sqlite3_exec(p->db, "DROP TABLE IF EXISTS temp."UNIQUE_TABLE_NAME,0,0,0);
  return rc;
}

/*
** Allocate a new sqlite3expert object.
*/
sqlite3expert *sqlite3_expert_new(sqlite3 *db, char **pzErrmsg){
................................................................................
  ** will contain a virtual table corresponding to each real table in
  ** the user database schema, and a copy of each view. It is used to
  ** collect information regarding the WHERE, ORDER BY and other clauses
  ** of the user's query.
  */
  if( rc==SQLITE_OK ){
    pNew->db = db;
    pNew->iSample = 100;
    rc = sqlite3_open(":memory:", &pNew->dbv);
  }
  if( rc==SQLITE_OK ){
    rc = sqlite3_open(":memory:", &pNew->dbm);
    if( rc==SQLITE_OK ){
      sqlite3_db_config(pNew->dbm, SQLITE_DBCONFIG_FULL_EQP, 1, (int*)0);
    }
................................................................................
  ** return the new sqlite3expert handle.  */
  if( rc!=SQLITE_OK ){
    sqlite3_expert_destroy(pNew);
    pNew = 0;
  }
  return pNew;
}

/*
** Configure an sqlite3expert object.
*/
int sqlite3_expert_config(sqlite3expert *p, int op, ...){
  int rc = SQLITE_OK;
  va_list ap;
  va_start(ap, op);
  switch( op ){
    case EXPERT_CONFIG_SAMPLE: {
      int iVal = va_arg(ap, int);
      if( iVal<0 ) iVal = 0;
      if( iVal>100 ) iVal = 100;
      p->iSample = iVal;
      break;
    }
    default:
      rc = SQLITE_NOTFOUND;
      break;
  }

  va_end(ap);
  return rc;
}

/*
** Add an SQL statement to the analysis.
*/
int sqlite3_expert_sql(
  sqlite3expert *p,               /* From sqlite3_expert_new() */
  const char *zSql,               /* SQL statement to add */

Changes to ext/expert/sqlite3expert.h.

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** to NULL. Or, if an error occurs, NULL is returned and (*pzErr) set to
** an English-language error message. In this case it is the responsibility
** of the caller to eventually free the error message buffer using
** sqlite3_free().
*/
sqlite3expert *sqlite3_expert_new(sqlite3 *db, char **pzErr);

































/*
** Specify zero or more SQL statements to be included in the analysis.
**
** Buffer zSql must contain zero or more complete SQL statements. This
** function parses all statements contained in the buffer and adds them
** to the internal list of statements to analyze. If successful, SQLITE_OK
** is returned and (*pzErr) set to NULL. Or, if an error occurs - for example
................................................................................
** immediately and no statements are added to the analysis.
*/
int sqlite3_expert_sql(
  sqlite3expert *p,               /* From a successful sqlite3_expert_new() */
  const char *zSql,               /* SQL statement(s) to add */
  char **pzErr                    /* OUT: Error message (if any) */
);


/*
** This function is called after the sqlite3expert object has been configured
** with all SQL statements using sqlite3_expert_sql() to actually perform
** the analysis. Once this function has been called, it is not possible to
** add further SQL statements to the analysis.
**







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** to NULL. Or, if an error occurs, NULL is returned and (*pzErr) set to
** an English-language error message. In this case it is the responsibility
** of the caller to eventually free the error message buffer using
** sqlite3_free().
*/
sqlite3expert *sqlite3_expert_new(sqlite3 *db, char **pzErr);

/*
** Configure an sqlite3expert object.
**
** EXPERT_CONFIG_SAMPLE:
**   By default, sqlite3_expert_analyze() generates sqlite_stat1 data for
**   each candidate index. This involves scanning and sorting the entire
**   contents of each user database table once for each candidate index
**   associated with the table. For large databases, this can be 
**   prohibitively slow. This option allows the sqlite3expert object to
**   be configured so that sqlite_stat1 data is instead generated based on a
**   subset of each table, or so that no sqlite_stat1 data is used at all.
**
**   A single integer argument is passed to this option. If the value is less
**   than or equal to zero, then no sqlite_stat1 data is generated or used by
**   the analysis - indexes are recommended based on the database schema only.
**   Or, if the value is 100 or greater, complete sqlite_stat1 data is
**   generated for each candidate index (this is the default). Finally, if the
**   value falls between 0 and 100, then it represents the percentage of user
**   table rows that should be considered when generating sqlite_stat1 data.
**
**   Examples:
**
**     // Do not generate any sqlite_stat1 data
**     sqlite3_expert_config(pExpert, EXPERT_CONFIG_SAMPLE, 0);
**
**     // Generate sqlite_stat1 data based on 10% of the rows in each table.
**     sqlite3_expert_config(pExpert, EXPERT_CONFIG_SAMPLE, 10);
*/
int sqlite3_expert_config(sqlite3expert *p, int op, ...);

#define EXPERT_CONFIG_SAMPLE 1    /* int */

/*
** Specify zero or more SQL statements to be included in the analysis.
**
** Buffer zSql must contain zero or more complete SQL statements. This
** function parses all statements contained in the buffer and adds them
** to the internal list of statements to analyze. If successful, SQLITE_OK
** is returned and (*pzErr) set to NULL. Or, if an error occurs - for example
................................................................................
** immediately and no statements are added to the analysis.
*/
int sqlite3_expert_sql(
  sqlite3expert *p,               /* From a successful sqlite3_expert_new() */
  const char *zSql,               /* SQL statement(s) to add */
  char **pzErr                    /* OUT: Error message (if any) */
);


/*
** This function is called after the sqlite3expert object has been configured
** with all SQL statements using sqlite3_expert_sql() to actually perform
** the analysis. Once this function has been called, it is not possible to
** add further SQL statements to the analysis.
**