**                  Or, if the main table is being written, a NULL value.
**
**   "row"       -> Number of rows for this object already processed
**
**   "progress"  -> total number of key/value b-tree operations performed
**                  so far as part of this ota update.
*/
#define OTA_CREATE_STATE "CREATE TABLE IF NOT EXISTS ota_state"        \
                             "(tbl, idx, row, progress)"

typedef struct OtaState OtaState;
typedef struct OtaObjIter OtaObjIter;
typedef unsigned char u8;

/*
................................................................................
  sqlite3_stmt *pInsert;          /* Statement for INSERT operations */
};

/*
** OTA handle.
*/
struct sqlite3ota {
  sqlite3 *dbDest;                /* Target db */
  sqlite3 *dbOta;                 /* Ota db */
  char *zTarget;                  /* Path to target db */

  int rc;                         /* Value returned by last ota_step() call */
  char *zErrmsg;                  /* Error message if rc!=SQLITE_OK */

  int nStep;                      /* Rows processed for current object */
  OtaObjIter objiter;
};

/*
** Prepare the SQL statement in buffer zSql against database handle db.
** If successful, set *ppStmt to point to the new statement and return
................................................................................
** left in the OTA handle passed as the first argument. A copy of the 
** error code is returned.
*/
static int otaObjIterFirst(sqlite3ota *p, OtaObjIter *pIter){
  int rc;
  memset(pIter, 0, sizeof(OtaObjIter));

  rc = prepareAndCollectError(p->dbOta, &pIter->pTblIter, &p->zErrmsg, 
      "SELECT substr(name, 6) FROM sqlite_master "
      "WHERE type='table' AND name LIKE 'data_%'"
  );

  if( rc==SQLITE_OK ){
    rc = prepareAndCollectError(p->dbDest, &pIter->pIdxIter, &p->zErrmsg,
        "SELECT name FROM sqlite_master "
        "WHERE type='index' AND tbl_name = ?"
    );
  }

  pIter->bCleanup = 1;
  p->rc = rc;
  return otaObjIterNext(p, pIter);
................................................................................
  if( pIter->azTblCol==0 ){
    sqlite3_stmt *pStmt;
    char *zSql;
    int nCol = 0;
    int bSeenPk = 0;
    int rc2;                      /* sqlite3_finalize() return value */

    zSql = sqlite3_mprintf("PRAGMA table_info(%Q)", pIter->zTbl);
    p->rc = prepareFreeAndCollectError(p->dbDest, &pStmt, &p->zErrmsg, zSql);
    while( p->rc==SQLITE_OK && SQLITE_ROW==sqlite3_step(pStmt) ){
      if( (nCol % 8)==0 ){
        int nByte = sizeof(char*) * (nCol+8);
        char **azNew = (char**)sqlite3_realloc(pIter->azTblCol, nByte);
        u8 *abNew = (u8*)sqlite3_realloc(pIter->azTblCol, nCol+8);

        if( azNew ) pIter->azTblCol = azNew;
................................................................................

    if( zIdx ){
      int *aiCol;                 /* Column map */

      /* Create the index writer */
      if( p->rc==SQLITE_OK ){
        p->rc = sqlite3_index_writer(
            p->dbDest, 0, zIdx, &pIter->pInsert, &aiCol, &pIter->nCol
        );
      }

      /* Create the SELECT statement to read keys in sorted order */
      zCollist = otaObjIterGetCollist(p, pIter, pIter->nCol, aiCol);
      if( p->rc==SQLITE_OK ){
        p->rc = prepareFreeAndCollectError(p->dbOta, &pIter->pSelect, pz,
            sqlite3_mprintf(
              "SELECT %s FROM 'data_%q' ORDER BY %s%s",
              zCollist, pIter->zTbl, zCollist, zLimit
            )
        );
      }
    }else{
      char *zBindings = otaObjIterGetBindlist(p, pIter->nTblCol);
      zCollist = otaObjIterGetCollist(p, pIter, pIter->nTblCol, 0);
      pIter->nCol = pIter->nTblCol;

      /* Create the SELECT statement to read keys from data_xxx */
      if( p->rc==SQLITE_OK ){
        p->rc = prepareFreeAndCollectError(p->dbOta, &pIter->pSelect, pz,
            sqlite3_mprintf(
              "SELECT %s FROM 'data_%q'%s", 
              zCollist, pIter->zTbl, zLimit)
        );
      }

      /* Create the INSERT statement to write to the target PK b-tree */
      if( p->rc==SQLITE_OK ){
        p->rc = prepareFreeAndCollectError(p->dbDest, &pIter->pInsert, pz,
            sqlite3_mprintf(

              "INSERT INTO %Q(%s) VALUES(%s)", pIter->zTbl, zCollist, zBindings
            )
        );
      }
      sqlite3_free(zBindings);
    }
    sqlite3_free(zCollist);
    sqlite3_free(zLimit);
................................................................................
    if( p->rc==SQLITE_OK && pIter->zTbl==0 ){
      p->rc = SQLITE_DONE;
    }
  }
  return p->rc;
}

static void otaOpenDatabase(sqlite3ota *p, sqlite3 **pDb, const char *zFile){













  if( p->rc==SQLITE_OK ){
    p->rc = sqlite3_open(zFile, pDb);


    if( p->rc ){
      const char *zErr = sqlite3_errmsg(*pDb);
      p->zErrmsg = sqlite3_mprintf("sqlite3_open(): %s", zErr);



    }
  }


}

static void otaSaveTransactionState(sqlite3ota *p){
  char *zInsert;

  zInsert = sqlite3_mprintf(
    "INSERT OR REPLACE INTO ota_state(rowid, tbl, idx, row, progress)"
    "VALUES(1, %Q, %Q, %d, NULL)",
    p->objiter.zTbl, p->objiter.zIdx, p->nStep
  );

  if( zInsert==0 ){
    p->rc = SQLITE_NOMEM;
  }else{
    p->rc = sqlite3_exec(p->dbOta, zInsert, 0, 0, &p->zErrmsg);
    if( p->rc==SQLITE_OK ){
      p->rc = sqlite3_exec(p->dbOta, "COMMIT", 0, 0, &p->zErrmsg);
    }
  }

  sqlite3_free(zInsert);
}

/*
** Allocate an OtaState object and load the contents of the ota_state 
** table into it. Return a pointer to the new object. It is the 
** responsibility of the caller to eventually free the object using
** sqlite3_free().
**
** If an error occurs, leave an error code and message in the ota handle
** and return NULL.
*/
static OtaState *otaLoadState(sqlite3ota *p){
  const char *zSelect = "SELECT tbl, idx, row, progress FROM ota_state";
  OtaState *pRet = 0;
  sqlite3_stmt *pStmt;
  int rc;

  assert( p->rc==SQLITE_OK );
  rc = prepareAndCollectError(p->dbOta, &pStmt, &p->zErrmsg, zSelect);
  if( rc==SQLITE_OK ){
    if( sqlite3_step(pStmt)==SQLITE_ROW ){
      const char *zIdx = (const char*)sqlite3_column_text(pStmt, 1);
      const char *zTbl = (const char*)sqlite3_column_text(pStmt, 0);
      int nIdx = zIdx ? (strlen(zIdx) + 1) : 0;
      int nTbl = strlen(zTbl) + 1;
      int nByte = sizeof(OtaState) + nTbl + nIdx;
................................................................................
  if( p ){
    OtaState *pState = 0;

    /* Open the target database */
    memset(p, 0, sizeof(sqlite3ota));
    p->zTarget = (char*)&p[1];
    memcpy(p->zTarget, zTarget, nTarget+1);
    otaOpenDatabase(p, &p->dbDest, zTarget);
    otaOpenDatabase(p, &p->dbOta, zOta);




    /* If it has not already been created, create the ota_state table */
    if( p->rc==SQLITE_OK ){
      p->rc = sqlite3_exec(p->dbOta, OTA_CREATE_STATE, 0, 0, &p->zErrmsg);
    }

    if( p->rc==SQLITE_OK ){
      pState = otaLoadState(p);
      if( pState && pState->zTbl==0 ){
        otaDeleteOalFile(p);
      }
................................................................................
    if( p->rc==SQLITE_OK ){
      const char *zScript =
        "PRAGMA journal_mode=off;"
        "PRAGMA pager_ota_mode=1;"
        "PRAGMA ota_mode=1;"
        "BEGIN IMMEDIATE;"
      ;
      p->rc = sqlite3_exec(p->dbDest, zScript, 0, 0, &p->zErrmsg);
    }

    if( p->rc==SQLITE_OK ){
      const char *zScript = "BEGIN IMMEDIATE";
      p->rc = sqlite3_exec(p->dbOta, zScript, 0, 0, &p->zErrmsg);
    }

    /* Point the object iterator at the first object */
    if( p->rc==SQLITE_OK ){
      p->rc = otaObjIterFirst(p, &p->objiter);
    }

................................................................................
    }

    /* Close all open statement handles. */
    otaObjIterFinalize(&p->objiter);

    /* Commit the transaction to the *-oal file. */
    if( p->rc==SQLITE_OK || p->rc==SQLITE_DONE ){
      rc = sqlite3_exec(p->dbDest, "COMMIT", 0, 0, &p->zErrmsg);
      if( rc!=SQLITE_OK ) p->rc = rc;
    }

    assert( sqlite3_next_stmt(p->dbDest, 0)==0 );
    assert( sqlite3_next_stmt(p->dbOta, 0)==0 );

    /* Close the open database handles */
    sqlite3_close(p->dbDest);
    sqlite3_close(p->dbOta);

    /* If the OTA has been completely applied and no error occurred, move
    ** the *-oal file to *-wal. */
    if( p->rc==SQLITE_DONE ){
      otaMoveOalFile(p);
    }

**                  Or, if the main table is being written, a NULL value.
**
**   "row"       -> Number of rows for this object already processed
**
**   "progress"  -> total number of key/value b-tree operations performed
**                  so far as part of this ota update.
*/
#define OTA_CREATE_STATE "CREATE TABLE IF NOT EXISTS ota.ota_state"        \
                             "(tbl, idx, row, progress)"

typedef struct OtaState OtaState;
typedef struct OtaObjIter OtaObjIter;
typedef unsigned char u8;

/*
................................................................................
  sqlite3_stmt *pInsert;          /* Statement for INSERT operations */
};

/*
** OTA handle.
*/
struct sqlite3ota {
  sqlite3 *db;                    /* "main" -> target db, "ota" -> ota db */

  char *zTarget;                  /* Path to target db */

  int rc;                         /* Value returned by last ota_step() call */
  char *zErrmsg;                  /* Error message if rc!=SQLITE_OK */

  int nStep;                      /* Rows processed for current object */
  OtaObjIter objiter;
};

/*
** Prepare the SQL statement in buffer zSql against database handle db.
** If successful, set *ppStmt to point to the new statement and return
................................................................................
** left in the OTA handle passed as the first argument. A copy of the 
** error code is returned.
*/
static int otaObjIterFirst(sqlite3ota *p, OtaObjIter *pIter){
  int rc;
  memset(pIter, 0, sizeof(OtaObjIter));

  rc = prepareAndCollectError(p->db, &pIter->pTblIter, &p->zErrmsg, 
      "SELECT substr(name, 6) FROM ota.sqlite_master "
      "WHERE type='table' AND name LIKE 'data_%'"
  );

  if( rc==SQLITE_OK ){
    rc = prepareAndCollectError(p->db, &pIter->pIdxIter, &p->zErrmsg,
        "SELECT name FROM main.sqlite_master "
        "WHERE type='index' AND tbl_name = ?"
    );
  }

  pIter->bCleanup = 1;
  p->rc = rc;
  return otaObjIterNext(p, pIter);
................................................................................
  if( pIter->azTblCol==0 ){
    sqlite3_stmt *pStmt;
    char *zSql;
    int nCol = 0;
    int bSeenPk = 0;
    int rc2;                      /* sqlite3_finalize() return value */

    zSql = sqlite3_mprintf("PRAGMA main.table_info(%Q)", pIter->zTbl);
    p->rc = prepareFreeAndCollectError(p->db, &pStmt, &p->zErrmsg, zSql);
    while( p->rc==SQLITE_OK && SQLITE_ROW==sqlite3_step(pStmt) ){
      if( (nCol % 8)==0 ){
        int nByte = sizeof(char*) * (nCol+8);
        char **azNew = (char**)sqlite3_realloc(pIter->azTblCol, nByte);
        u8 *abNew = (u8*)sqlite3_realloc(pIter->azTblCol, nCol+8);

        if( azNew ) pIter->azTblCol = azNew;
................................................................................

    if( zIdx ){
      int *aiCol;                 /* Column map */

      /* Create the index writer */
      if( p->rc==SQLITE_OK ){
        p->rc = sqlite3_index_writer(
            p->db, 0, zIdx, &pIter->pInsert, &aiCol, &pIter->nCol
        );
      }

      /* Create the SELECT statement to read keys in sorted order */
      zCollist = otaObjIterGetCollist(p, pIter, pIter->nCol, aiCol);
      if( p->rc==SQLITE_OK ){
        p->rc = prepareFreeAndCollectError(p->db, &pIter->pSelect, pz,
            sqlite3_mprintf(
              "SELECT %s FROM ota.'data_%q' ORDER BY %s%s",
              zCollist, pIter->zTbl, zCollist, zLimit
            )
        );
      }
    }else{
      char *zBindings = otaObjIterGetBindlist(p, pIter->nTblCol);
      zCollist = otaObjIterGetCollist(p, pIter, pIter->nTblCol, 0);
      pIter->nCol = pIter->nTblCol;

      /* Create the SELECT statement to read keys from data_xxx */
      if( p->rc==SQLITE_OK ){
        p->rc = prepareFreeAndCollectError(p->db, &pIter->pSelect, pz,
            sqlite3_mprintf(
              "SELECT %s FROM ota.'data_%q'%s", 
              zCollist, pIter->zTbl, zLimit)
        );
      }

      /* Create the INSERT statement to write to the target PK b-tree */
      if( p->rc==SQLITE_OK ){
        p->rc = prepareFreeAndCollectError(p->db, &pIter->pInsert, pz,
            sqlite3_mprintf(
              "INSERT INTO main.%Q(%s) VALUES(%s)", 
              pIter->zTbl, zCollist, zBindings
            )
        );
      }
      sqlite3_free(zBindings);
    }
    sqlite3_free(zCollist);
    sqlite3_free(zLimit);
................................................................................
    if( p->rc==SQLITE_OK && pIter->zTbl==0 ){
      p->rc = SQLITE_DONE;
    }
  }
  return p->rc;
}


/*
** Argument zFmt is a sqlite3_mprintf() style format string. The trailing
** arguments are the usual subsitution values. This function performs
** the printf() style substitutions and executes the result as an SQL
** statement on the OTA handles database.
**
** If an error occurs, an error code and error message is stored in the
** OTA handle. If an error has already occurred when this function is
** called, it is a no-op.
*/
static int otaMPrintfExec(sqlite3ota *p, const char *zFmt, ...){
  va_list ap;
  va_start(ap, zFmt);
  if( p->rc==SQLITE_OK ){

    char *zSql = sqlite3_vmprintf(zFmt, ap);
    if( zSql==0 ){
      p->rc = SQLITE_NOMEM;


    }else{
      p->rc = sqlite3_exec(p->db, zSql, 0, 0, &p->zErrmsg);
      sqlite3_free(zSql);
    }
  }
  va_end(ap);
  return p->rc;
}

static void otaSaveTransactionState(sqlite3ota *p){
  otaMPrintfExec(p, 


    "INSERT OR REPLACE INTO ota.ota_state(rowid, tbl, idx, row, progress)"
    "VALUES(1, %Q, %Q, %d, NULL)",
    p->objiter.zTbl, p->objiter.zIdx, p->nStep
  );











}

/*
** Allocate an OtaState object and load the contents of the ota_state 
** table into it. Return a pointer to the new object. It is the 
** responsibility of the caller to eventually free the object using
** sqlite3_free().
**
** If an error occurs, leave an error code and message in the ota handle
** and return NULL.
*/
static OtaState *otaLoadState(sqlite3ota *p){
  const char *zSelect = "SELECT tbl, idx, row, progress FROM ota.ota_state";
  OtaState *pRet = 0;
  sqlite3_stmt *pStmt;
  int rc;

  assert( p->rc==SQLITE_OK );
  rc = prepareAndCollectError(p->db, &pStmt, &p->zErrmsg, zSelect);
  if( rc==SQLITE_OK ){
    if( sqlite3_step(pStmt)==SQLITE_ROW ){
      const char *zIdx = (const char*)sqlite3_column_text(pStmt, 1);
      const char *zTbl = (const char*)sqlite3_column_text(pStmt, 0);
      int nIdx = zIdx ? (strlen(zIdx) + 1) : 0;
      int nTbl = strlen(zTbl) + 1;
      int nByte = sizeof(OtaState) + nTbl + nIdx;
................................................................................
  if( p ){
    OtaState *pState = 0;

    /* Open the target database */
    memset(p, 0, sizeof(sqlite3ota));
    p->zTarget = (char*)&p[1];
    memcpy(p->zTarget, zTarget, nTarget+1);
    p->rc = sqlite3_open(zTarget, &p->db);
    if( p->rc ){
      p->zErrmsg = sqlite3_mprintf("%s", sqlite3_errmsg(p->db));
    }
    otaMPrintfExec(p, "ATTACH %Q AS ota", zOta);

    /* If it has not already been created, create the ota_state table */
    if( p->rc==SQLITE_OK ){
      p->rc = sqlite3_exec(p->db, OTA_CREATE_STATE, 0, 0, &p->zErrmsg);
    }

    if( p->rc==SQLITE_OK ){
      pState = otaLoadState(p);
      if( pState && pState->zTbl==0 ){
        otaDeleteOalFile(p);
      }
................................................................................
    if( p->rc==SQLITE_OK ){
      const char *zScript =
        "PRAGMA journal_mode=off;"
        "PRAGMA pager_ota_mode=1;"
        "PRAGMA ota_mode=1;"
        "BEGIN IMMEDIATE;"
      ;





      p->rc = sqlite3_exec(p->db, zScript, 0, 0, &p->zErrmsg);
    }

    /* Point the object iterator at the first object */
    if( p->rc==SQLITE_OK ){
      p->rc = otaObjIterFirst(p, &p->objiter);
    }

................................................................................
    }

    /* Close all open statement handles. */
    otaObjIterFinalize(&p->objiter);

    /* Commit the transaction to the *-oal file. */
    if( p->rc==SQLITE_OK || p->rc==SQLITE_DONE ){
      rc = sqlite3_exec(p->db, "COMMIT", 0, 0, &p->zErrmsg);
      if( rc!=SQLITE_OK ) p->rc = rc;
    }




    /* Close the open database handles */

    sqlite3_close(p->db);

    /* If the OTA has been completely applied and no error occurred, move
    ** the *-oal file to *-wal. */
    if( p->rc==SQLITE_DONE ){
      otaMoveOalFile(p);
    }