PRB: 32K Limit on Direct Parameters for 16-bit Drivers

• Microsoft Open Database Connectivity, version 2.0

SYMPTOMS

If you use SQLBindParameter to directly pass more than 32K of data to a SQL statement against 16-bit desktop database drivers, you will get the following error message:

   SQL_ERROR: Memory allocation failure.

   //data source is an access table objtab with only one OLE field.
   //16-bit Access driver 2.00.2317 is used

   SQLPrepare(hstmt, "insert into objtab(?)", SQL_NTS);
   BigObj = AllocateMemory(sizeof(UCHAR) * 32800);
   cbBigObj = 32800;
   SQLBindParameter(
      hstmt, 1, SQL_PARAM_INPUT, SQL_C_BINARY, SQL_C_LONGVARCHAR,
      32800, 0, BigObj, 32800, &cbBigObj);
   //Prepare the BigObj
   SQLExecute(hstmt);

   SQL Error State:S1001; Native Error Code: 34;
   ODBC Error:[Microsoft][ODBC Microsoft Access 2.0 Driver]memory
   allocation failure.

CAUSE

The internal buffer for direct parameters passed to the 16-bit desktop database drivers is limited to 32K.

NOTE: You will actually have a little less than 32K of total parameters, because some space is taken up by a length byte in the internal buffer.

RESOLUTION

• Use 32-bit drivers if you can.
• Use SQLPutData to send it in installments. Using direct parameters is not recommended to pass in large data. Instead, you can use data-at-execution with SQLPutData.
• Use SQLExtendedFetch and SQLSetPos...SQL_ADD, which is faster. Because all of the parameters are not copied into a separate buffer before being passed into the internal buffer, you save a memcopy.