SQLite

  ** If this fails, or if opening the file failed, then close the file and 
  ** remove the entry from the db->aDb[] array. i.e. put everything back the
  ** way we found it.
  */
  if( rc==SQLITE_OK ){
    db->init.iDb = 0;
    db->mDbFlags &= ~(DBFLAG_SchemaKnownOk);
    if( !IsReuseSchema(db) && !REOPEN_AS_MEMDB(db) ){
      sqlite3BtreeEnterAll(db);
      rc = sqlite3Init(db, &zErrDyn);
      sqlite3BtreeLeaveAll(db);
      assert( zErrDyn==0 || rc!=SQLITE_OK );
    }
  }
#ifdef SQLITE_USER_AUTHENTICATION

** SQLITE_OK is returned if successful, or an SQLite error code otherwise. If
** an error code is returned, (*pzErr) may be set to point to a buffer
** containing an error message. It is the responsibility of the caller to
** eventually free this buffer using sqlite3_free().
*/
int sqlite3SchemaLoad(sqlite3 *db, int iDb, int *pbUnload, char **pzErr){
  int rc = SQLITE_OK;
  if( IsReuseSchema(db) 
      && DbHasProperty(db, iDb, DB_SchemaLoaded)==0 
      && (db->init.busy==0 || (iDb!=1 && db->init.iDb==1))
  ){
    struct sqlite3InitInfo sv = db->init;
    memset(&db->init, 0, sizeof(struct sqlite3InitInfo));
    rc = sqlite3InitOne(db, iDb, pzErr, 0);
    db->init = sv;

#endif
  while(1){
    for(i=OMIT_TEMPDB; i<db->nDb; i++){
      int j = (i<2) ? i^1 : i;   /* Search TEMP before MAIN */
      if( zDatabase==0 || sqlite3StrICmp(zDatabase, db->aDb[j].zDbSName)==0 ){
        int bUnload = 0;
        assert( sqlite3SchemaMutexHeld(db, j, 0) );
        if( IsReuseSchema(db) ){
          Parse *pParse = db->pParse;
          if( pParse && pParse->nErr==0 ){
            pParse->rc = sqlite3SchemaLoad(db, j, &bUnload, &pParse->zErrMsg);
            if( pParse->rc ) pParse->nErr++;
          }
        }
        p = sqlite3HashFind(&db->aDb[j].pSchema->tblHash, zName);

){
  Table *p;
  sqlite3 *db = pParse->db;

  /* Read the database schema. If an error occurs, leave an error message
  ** and code in pParse and return NULL. */
  if( (db->mDbFlags & DBFLAG_SchemaKnownOk)==0 
   && !IsReuseSchema(db)
   && SQLITE_OK!=sqlite3ReadSchema(pParse)
  ){
    return 0;
  }

  p = sqlite3FindTable(db, zName, zDbase);
  if( p==0 ){
#ifndef SQLITE_OMIT_VIRTUALTABLE
    /* If zName is the not the name of a table in the schema created using
    ** CREATE, then check to see if it is the name of an virtual table that
    ** can be an eponymous virtual table. */
    if( pParse->disableVtab==0 ){
      Module *pMod = (Module*)sqlite3HashFind(&db->aModule, zName);
      if( pMod==0 && sqlite3_strnicmp(zName, "pragma_", 7)==0 ){
        pMod = sqlite3PragmaVtabRegister(db, zName);
      }
      if( pMod ){
        if( IsReuseSchema(db) && pParse->nErr==0 ){
          int bDummy = 0;
          pParse->rc = sqlite3SchemaLoad(db, 0, &bDummy, &pParse->zErrMsg);
          if( pParse->rc ) pParse->nErr++;
        }
        if( sqlite3VtabEponymousTableInit(pParse, pMod) ){
          Table *pEpoTab = pMod->pEpoTab;
          assert( IsReuseSchema(db) || pEpoTab->pSchema==db->aDb[0].pSchema );
          pEpoTab->pSchema = db->aDb[0].pSchema;  /* For SHARED_SCHEMA mode */
          return pEpoTab;
        }
      }
    }
#endif
    if( flags & LOCATE_NOERR ) return 0;
    pParse->checkSchema = 1;
  }else if( IsVirtual(p) && pParse->disableVtab ){
    p = 0;
  }

  if( p==0 && (!IsReuseSchema(db) || pParse->nErr==0) ){
    const char *zMsg = flags & LOCATE_VIEW ? "no such view" : "no such table";
    if( zDbase ){
      sqlite3ErrorMsg(pParse, "%s: %s.%s", zMsg, zDbase, zName);
    }else{
      sqlite3ErrorMsg(pParse, "%s: %s", zMsg, zName);
    }
  }

  ** it does. The exception is if the statement being parsed was passed
  ** to an sqlite3_declare_vtab() call. In that case only the column names
  ** and types will be used, so there is no need to test for namespace
  ** collisions.
  */
  if( !IN_SPECIAL_PARSE ){
    char *zDb = db->aDb[iDb].zDbSName;
    if( !IsReuseSchema(db) && SQLITE_OK!=sqlite3ReadSchema(pParse) ){
      goto begin_table_error;
    }
    pTable = sqlite3FindTable(db, zName, zDb);
    if( pTable ){
      if( !noErr ){
        sqlite3ErrorMsg(pParse, "table %T already exists", pName);
      }else{

  int iDb;

  if( db->mallocFailed ){
    goto exit_drop_table;
  }
  assert( pParse->nErr==0 );
  assert( pName->nSrc==1 );
  if( !IsReuseSchema(db) && sqlite3ReadSchema(pParse) ) goto exit_drop_table;
  if( noErr ) db->suppressErr++;
  assert( isView==0 || isView==LOCATE_VIEW );
  pTab = sqlite3LocateTableItem(pParse, isView, &pName->a[0]);
  if( noErr ) db->suppressErr--;

  if( pTab==0 ){
    if( noErr ) sqlite3CodeVerifyNamedSchema(pParse, pName->a[0].zDatabase);

  if( db->mallocFailed || pParse->nErr>0 ){
    goto exit_create_index;
  }
  if( IN_DECLARE_VTAB && idxType!=SQLITE_IDXTYPE_PRIMARYKEY ){
    goto exit_create_index;
  }
  if( !IsReuseSchema(db) && SQLITE_OK!=sqlite3ReadSchema(pParse) ){
    goto exit_create_index;
  }

  /*
  ** Find the table that is to be indexed.  Return early if not found.
  */
  if( pTblName!=0 ){

  Schema *pSchema;                /* Linked list of Schema objects */
  Schema sSchema;                 /* The single dummy schema object */
  SchemaPool *pNext;              /* Next element in schemaPoolList */
};

#ifdef SQLITE_DEBUG
static void assert_schema_state_ok(sqlite3 *db){
  if( IsReuseSchema(db) && db->magic!=SQLITE_MAGIC_ZOMBIE ){
    int i;
    for(i=0; i<db->nDb; i++){
      if( i!=1 ){
        Db *pDb = &db->aDb[i];
        Btree *pBt = pDb->pBt;
        assert( pBt==0 || sqlite3BtreeSchema(pBt, 0, 0)==0 );
        assert( pDb->pSchema );

** database iDb. 
**
** If an OOM error occurs while disconnecting from a schema-pool, 
** the db->mallocFailed flag is set.
*/
void sqlite3SchemaClearOrDisconnect(sqlite3 *db, int iDb){
  Db *pDb = &db->aDb[iDb];
  if( IsReuseSchema(db) && iDb!=1 && pDb->pSPool ){
    sqlite3SchemaDisconnect(db, iDb, 1);
  }else{
    sqlite3SchemaClear(pDb->pSchema);
  }
}

/*

/*
** Check that the schema of db iDb is writable (either because it is the 
** temp db schema or because the db handle was opened without
** SQLITE_OPEN_SHARED_SCHEMA). If so, do nothing. Otherwise, leave an 
** error in the Parse object.
*/
void sqlite3SchemaWritable(Parse *pParse, int iDb){
  if( iDb!=1 && (pParse->db->openFlags & SQLITE_OPEN_SHARED_SCHEMA) 
   && IN_DECLARE_VTAB==0
  ){
    sqlite3ErrorMsg(pParse, "attempt to modify read-only schema");
  }
}

/*
** The schema object passed as the only argument was allocated using
** sqlite3_malloc() and then populated using the usual mechanism. This

** If the bNew parameter is true, then this function may allocate memory. 
** If the allocation attempt fails, then SQLITE_NOMEM is returned and the
** schema-pool is not disconnected from. Or, if no OOM error occurs, 
** SQLITE_OK is returned.
*/
int sqlite3SchemaDisconnect(sqlite3 *db, int iDb, int bNew){
  int rc = SQLITE_OK;
  if( IsReuseSchema(db) ){
    Db *pDb = &db->aDb[iDb];
    SchemaPool *pSPool = pDb->pSPool;
    assert_schema_state_ok(db);
    assert( pDb->pSchema );

    if( pSPool==0 ){
      assert( pDb->pVTable==0 );

** with BTree handle pBt, creating a new one if necessary. However, if
** the database handle was opened with the SQLITE_OPEN_SHARED_SCHEMA flag
** specified, a new, empty, Schema object in memory obtained by 
** sqlite3_malloc() is always returned.
*/
Schema *sqlite3SchemaGet(sqlite3 *db, Btree *pBt){
  Schema *p;
  if( pBt && (db->openFlags & SQLITE_OPEN_SHARED_SCHEMA)==0 ){
    p = (Schema*)sqlite3BtreeSchema(pBt, sizeof(Schema), sqlite3SchemaClear);
  }else{
    db->lookaside.bDisable++;
    p = (Schema*)sqlite3DbMallocZero(db, sizeof(Schema));
    db->lookaside.bDisable--;
  }
  if( !p ){

    Schema *pSchema = db->aDb[i].pSchema;
    if( pSchema ){
      for(p=sqliteHashFirst(&pSchema->tblHash); p; p=sqliteHashNext(p)){
        Table *pTab = (Table *)sqliteHashData(p);
        if( IsVirtual(pTab) ) sqlite3VtabDisconnect(db, pTab);
      }
    }
    if( i!=1 && IsReuseSchema(db) ){
      VTable *pVTable;
      VTable *pNext;
      for(pVTable=db->aDb[i].pVTable; pVTable; pVTable=pNext){
        pNext = pVTable->pNext;
        sqlite3VtabUnlock(pVTable);
      }
      db->aDb[i].pVTable = 0;

  }
#endif

  /* Ensure the database schema has been loaded */
  sqlite3_mutex_enter(db->mutex);
  bUnlock = sqlite3LockReusableSchema(db);
  sqlite3BtreeEnterAll(db);
  if( IsReuseSchema(db)==0 ){
    rc = sqlite3Init(db, &zErrMsg);
  }

  /* Locate the table in question */
  if( rc==SQLITE_OK ){
    Parse sParse;                   /* Fake Parse object for FindTable */
    Parse *pSaved = db->pParse;

  /* Locate the pragma in the lookup table */
  pPragma = pragmaLocate(zLeft);
  if( pPragma==0 ) goto pragma_out;

  /* Make sure the database schema is loaded if the pragma requires that */
  if( (pPragma->mPragFlg & PragFlg_NeedSchema)!=0 ){
    if( IsReuseSchema(db) && (zDb || (pPragma->mPragFlg & PragFlg_OneSchema)) ){
      assert( iDb>=0 && iDb<db->nDb );
      pParse->rc = sqlite3SchemaLoad(db, iDb, 0, &pParse->zErrMsg);
      if( pParse->rc ) goto pragma_out;
    }else{
      if( sqlite3ReadSchema(pParse) ) goto pragma_out;
    }
  }

  }else if( pData->pzErrMsg[0]!=0 ){
    /* A error message has already been generated.  Do not overwrite it */
  }else if( pData->mInitFlags & INITFLAG_AlterTable ){
    *pData->pzErrMsg = sqlite3DbStrDup(db, zExtra);
    pData->rc = SQLITE_ERROR;
  }else if( db->flags & SQLITE_WriteSchema ){
    pData->rc = SQLITE_CORRUPT_BKPT;
  }else if( IsReuseSchema(db) 
         && 0==sqlite3StrNICmp(zExtra, "malformed database schema", 17)
  ){
    pData->rc = SQLITE_CORRUPT_BKPT;
    *pData->pzErrMsg = sqlite3DbStrDup(db, zExtra);
  }else{
    char *z;
    if( zObj==0 ) zObj = "?";

     || pIndex->tnum<2
     || sqlite3IndexHasDuplicateRootPage(pIndex)
    ){
      corruptSchema(pData, argv[0], pIndex?"invalid rootpage":"orphan index");
    }
  }

  if( iDb!=1 && (db->openFlags & SQLITE_OPEN_SHARED_SCHEMA) ){
    schemaUpdateChecksum(pData, argv[0], argv[1], argv[2]);
  }
  return 0;
}

/*
** Attempt to read the database schema and initialize internal

  int meta[5];
  InitData initData;
  const char *zMasterName;
  int openedTransaction = 0;

  assert( (db->mDbFlags & DBFLAG_SchemaKnownOk)==0 );
  assert( iDb>=0 && iDb<db->nDb );
  assert( db->aDb[iDb].pSchema || (IsReuseSchema(db) && iDb!=1) );
  assert( sqlite3_mutex_held(db->mutex) );
  assert( iDb==1 || sqlite3BtreeHoldsMutex(db->aDb[iDb].pBt) );

  pDb = &db->aDb[iDb];
  assert( pDb->pSPool==0 || IsReuseSchema(db) );
  if( pDb->pSPool ){
    /* See if there is a free schema object in the schema-pool. If not,
    ** disconnect from said schema pool and continue. This function will
    ** connect to a (possibly different) schema-pool before returning. */
    Schema *pNew = sqlite3SchemaExtract(pDb->pSPool);
    if( pNew ){
      pDb->pSchema = pNew;

    ** purpose of this is to allow access to the sqlite_master table
    ** even when its contents have been corrupted.
    */
    DbSetProperty(db, iDb, DB_SchemaLoaded);
    rc = SQLITE_OK;
  }

  if( rc==SQLITE_OK && iDb!=1 && (db->openFlags & SQLITE_OPEN_SHARED_SCHEMA) ){
    rc = sqlite3SchemaConnect(db, iDb, initData.cksum);
  }

  /* Jump here for an error that occurs after successfully allocating
  ** curMain and calling sqlite3BtreeEnter(). For an error that occurs
  ** before that point, jump to error_out.
  */

    sqlite3ResetOneSchema(db, iDb);
  }
  db->init.busy = 0;
  return rc;
}

int sqlite3LockReusableSchema(sqlite3 *db){
  if( IsReuseSchema(db) && (db->mDbFlags & DBFLAG_SchemaInuse)==0 ){
    db->mDbFlags |= DBFLAG_SchemaInuse;
    return 1;
  }
  return 0;
}
void sqlite3UnlockReusableSchema(sqlite3 *db, int bRelease){
  if( bRelease ){

  assert( sqlite3_mutex_held(db->mutex) );
  if( !db->init.busy ){
    db->mDbFlags |= DBFLAG_FreeSchema;      /* For sharable-schema mode */
    rc = sqlite3Init(db, &pParse->zErrMsg);
    if( rc!=SQLITE_OK ){
      pParse->rc = rc;
      pParse->nErr++;
    }else if( db->noSharedCache && !IsReuseSchema(db) ){
      db->mDbFlags |= DBFLAG_SchemaKnownOk;
    }
  }
  return rc;
}

  sqlite3 *pNextBlocked;        /* Next in list of all blocked connections */
#endif
#ifdef SQLITE_USER_AUTHENTICATION
  sqlite3_userauth auth;        /* User authentication information */
#endif
};

#define IsReuseSchema(db) (((db)->openFlags & SQLITE_OPEN_SHARED_SCHEMA)!=0)

/*
** A macro to discover the encoding of a database.
*/
#define SCHEMA_ENC(db) ((db)->aDb[0].pSchema->enc)
#define ENC(db)        ((db)->enc)

  u8 op;                  /* One of TK_DELETE, TK_UPDATE, TK_INSERT         */
  u8 tr_tm;               /* One of TRIGGER_BEFORE, TRIGGER_AFTER */
  Expr *pWhen;            /* The WHEN clause of the expression (may be NULL) */
  IdList *pColumns;       /* If this is an UPDATE OF <column-list> trigger,
                             the <column-list> is stored here */
  Schema *pSchema;        /* Schema containing the trigger */
  Schema *pTabSchema;     /* Schema containing the table */
  char *zTabSchema;       /* Temp triggers in IsReuseSchema() dbs only */
  TriggerStep *step_list; /* Link list of trigger program steps             */
  Trigger *pNext;         /* Next trigger associated with the table */
};

/*
** A trigger is either a BEFORE or an AFTER trigger.  The following constants
** determine which.

    return 0;
  }

  if( pTmpSchema!=pTab->pSchema ){
    sqlite3 *db = pParse->db;
    HashElem *p;
    char *zSchema = 0;
    if( IsReuseSchema(db) ){
      zSchema = db->aDb[sqlite3SchemaToIndex(db, pTab->pSchema)].zDbSName;
    }
    assert( sqlite3SchemaMutexHeld(db, 0, pTmpSchema) );
    for(p=sqliteHashFirst(&pTmpSchema->trigHash); p; p=sqliteHashNext(p)){
      Trigger *pTrig = (Trigger *)sqliteHashData(p);
      if( (zSchema==0 && pTrig->pTabSchema==pTab->pSchema)
       || (zSchema!=0 && 0==sqlite3StrICmp(pTrig->zTabSchema, zSchema))

  /* Build the Trigger object */
  pTrigger = (Trigger*)sqlite3DbMallocZero(db, sizeof(Trigger));
  if( pTrigger==0 ) goto trigger_cleanup;
  pTrigger->zName = zName;
  zName = 0;
  pTrigger->table = sqlite3DbStrDup(db, pTableName->a[0].zName);
  if( IsReuseSchema(db) && iDb==1 ){
    int iTabDb = sqlite3SchemaToIndex(db, pTab->pSchema);
    pTrigger->zTabSchema = sqlite3DbStrDup(db, db->aDb[iTabDb].zDbSName);
  }
  pTrigger->pSchema = db->aDb[iDb].pSchema;
  pTrigger->pTabSchema = pTab->pSchema;
  pTrigger->op = (u8)op;
  pTrigger->tr_tm = tr_tm==TK_BEFORE ? TRIGGER_BEFORE : TRIGGER_AFTER;

** pTab is a pointer to a Table structure representing a virtual-table.
** Return a pointer to the VTable object used by connection db to access 
** this virtual-table, if one has been created, or NULL otherwise.
*/
VTable *sqlite3GetVTable(sqlite3 *db, Table *pTab){
  VTable *pVtab;
  assert( IsVirtual(pTab) );
  if( IsReuseSchema(db) ){
    int iDb = sqlite3SchemaToIndex(db, pTab->pSchema);
    if( iDb!=1 ){
      for(pVtab=db->aDb[iDb].pVTable; pVtab; pVtab=pVtab->pNext){
        if( sqlite3StrICmp(pTab->zName, pVtab->zName)==0 ) break;
      }
      return pVtab;
    }

      /* If everything went according to plan, link the new VTable structure
      ** into the linked list headed by pTab->pVTable. Or, if this is a
      ** reusable schema, into the linked list headed by Db.pVTable.
      **
      ** Then loop through the columns of the table to see if any of them
      ** contain the token "hidden". If so, set the Column COLFLAG_HIDDEN flag
      ** and remove the token from the type string.  */
      if( IsReuseSchema(db) && iDb!=1 ){
        pVTable->pNext = db->aDb[iDb].pVTable;
        db->aDb[iDb].pVTable = pVTable;
      }else{
        pVTable->pNext = pTab->pVTable;
        pTab->pVTable = pVTable;
      }