1. Data Warehousing Group Transaction Processing
Last Updated : 27th April 2004
Center of Excellence
Data Warehousing Group
Transaction Processing

2. Requests
A request to Teradata Database consists of one or more SQL statements.
Single Statement Requests
Multi Statement Requests.
An SQL statement can be submitted from
a BTEQ script
an embedded application program.
a stored procedure
a CLI, ODBC, JDBC program.

3. Multi-Statement Requests
A multi-statement request consists of multiple SQL statements separated by semicolon.
Treated as a single unit of work.
Either all statements in the request complete successfully or the entire request is aborted.
Multi-statement requests are non-ANSI SQL-99 standard.
Multi-statement requests improve performance by reducing processing overhead.

4. Transactions A transaction is a logical unit of work.
Statements nested within the transaction either execute successfully as a group or do not execute.
ANSI Mode
Teradata Mode.

5. ANSI Mode Transactions are always implicit in ANSI session mode.
A transaction initiates when :
The first SQL statement in a session executes
The first statement following the close of a session executes.
COMMIT or ROLLBACK/ABORT statements close a transaction.
If a transaction includes a DDL statement, it must be the last statement in the transaction.
Error results roll back only the present request not the entire transaction.

6. Teradata Mode
A Teradata SQL transaction can be a single SQL statement, or a sequence of SQL statements, treated as single unit of work.
Implicit
Explicit
Starts with BEGIN TRANSATION statement.
Ends with END TRANSACTION statement.
If a transaction includes a DDL statement, it must be the last statement in the transaction.
Error results roll back the entire transaction.
Transactions are atomic - either all requests are performed, or none are.

7. Transaction Locks Lock Levels Types of Locks Database Level Locks
Table Level Locks
Row Hash Locks
Types of Locks
Exclusive Locks
Write Locks
Read Locks
Access Locks

8. Locking Compatibility
Lock Mode Requested
Locking Mode Held
None
Access
Read
Write
Exclusive
Lock Granted
Request
Queued

9. A Deadlock Example BT; SELECT * FROM TABLE1; UPDATE table1
SET col1 = <value1>
WHERE col1 = pqr;
ET;
BT;
LOCK TABLE1 FOR WRITE;
SELECT * FROM TABLE1;
UPDATE table1
SET col1 = <value1>
WHERE col1 = pqr;
ET;
BT;
SELECT * FROM TABLE1;
UPDATE table1
SET col1 = <value1>
WHERE col1 = xyz;
ET;
BT;
LOCK TABLE1 FOR WRITE;
SELECT * FROM TABLE1;
UPDATE table1
SET col1 = <value1>
WHERE col1 = xyz;
ET;

10. Deadlock Prevention
Develop your applications to avoid deadlock situations.
Sometimes Deadlocks are unavoidable.
Plan for graceful recovery whenever a deadlock.
If a multistatement transaction aborted due to a deadlock, the entire transaction must be executed again.
Use “LOCK FOR ACCESS” modifier when “dirty reads” are accepatble.

11. Questions ?