[QODBC ALL] sp_batchupdate Throws AccessViolationException When SELECT Runs Before Batch Commands

Problem Description:

When using QODBC batch procedures (sp_batchstart, sp_batchclear, sp_batchupdate) in a .NET/C# application, executing any SELECT query before calling sp_batchstart causes the subsequent sp_batchupdate to throw a System.AccessViolationException:

Attempted to read or write protected memory. This is often an indication that other memory is corrupt.

Affected products: QODBC Desktop, .NET applications using ODBC connection strings
Expected outcome: A SELECT query before batch procedures should not interfere with batch operations. Batch updates should work regardless of prior SELECT statements on the same connection.

Symptoms:

• A .NET/C# application using a QODBC ODBC connection executes a normal SELECT query.
• Subsequently calling sp_batchstart, inserting/updating records, and then sp_batchupdate throws System.AccessViolationException.
• Removing the preceding SELECT statement makes the batch operation work correctly.
• The issue only occurs when a SELECT result set is left open or not fully consumed before beginning a batch sequence on the same connection.

Cause:

This is a known bug in QODBC Desktop (tracked as B01770). The QODBC driver's ODBC cursor state is not fully reset after a SELECT result set, which corrupts the connection state before batch operations begin.

Environment:

Workaround:

Do not execute any SELECT queries on the same ODBC connection before batch operations. If your application needs data from a SELECT query before running batch commands, use a separate ODBC connection for the SELECT operation.

1. Create two ODBC connections: Use one connection exclusively for data reads (SELECT queries) and another for batch write operations.
2. Close any result sets fully before starting a batch sequence on the same connection.
3. Reopen the connection before running sp_batchstart if a SELECT was used on it previously.

Keywords: