SQL Server - How to make SELECT block with TRANSACTION_SERIALIZABLE

Question

I'm in the process of switching an application to use SQL Server. Is there anyway of making a SELECT in SQL Server implement a lock (and therefore also get blocked) similar to an INSERT or UPDATE?
Essentially, I have code that tracks a transaction ID for a particular customer; given there can be concurrent access from the same customer, I am using TRANSACTION_SERIALIZABLE:
long id = 0L; // Customer ID stmt = Conn.prepareStatement("SELECT TxID FROM TxIDTable WHERE (ID = ?)"); stmt.setLong(1, id); result = stmt.executeQuery(); result.next(); int tx_id = result.getInt("TxID"); result.close(); stmt.close(); stmt = Conn.prepareStatement("UPDATE TxID SET TxID = ? WHERE (ID = ?)"); stmt.setInt(1, tx_id + 1); stmt.setLong(2, id); stmt.executeUpdate(); stmt.close(); Conn.commit();
This code is working, however on SQL Server I have to wrap a loop around it, and if I catch a deadlock exception, rerun the transaction. This is costly and I would much rather have the SELECT create a lock and therefore block any concurrent SELECTs. One workaround is to force a dummy UPDATE up front:
long id = 0L; // Customer ID stmt = Conn.prepareStatement("UPDATE TxIDTable SET ID = ? WHERE (ID = ?)"); stmt.setLong(1, id); // THIS UPDATE DOES NOT REALLY UPDATE ANYTHING stmt.setLong(2, id); // (NOTE SET AND WHERE CLAUSE ARE IDENTICAL) stmt.executeUpdate(); // HOWEVER, IT DOES EFFECTLY PREVENT DEADLOCK // BY CREATING A TABLE LOCK BEFORE THE SELECT stmt.close(); // stmt = Conn.prepareStatement("SELECT TxID FROM TxIDTable WHERE (ID = ?)"); stmt.setLong(1, id); result = stmt.executeQuery(); result.next(); int tx_id = result.getInt("TxID"); result.close(); stmt.close(); stmt = Conn.prepareStatement("UPDATE TxIDTable SET TxID = ? WHERE (ID = ?)"); stmt.setInt(1, tx_id + 1); stmt.setLong(2, id); stmt.executeUpdate(); stmt.close(); Conn.commit();
This seems really like a waste -- anyway to make the SELECT lock on SQL Server??
Thanks,
Kevin

Answer 1

You want a table hint (the equivalent of SELECT ... FOR UPDATE in other dialects):
[http://msdn2.microsoft.com/en-us/library/ms187373.aspx|http://msdn2.microsoft.com/en-us/library/ms187373.aspx]