Transaction Processing

Index:

  1. Commit Mode
  2. Isolation Levels
  3. Performance Hints

Commit Mode

There are two modes for managing transactions within JDBC:

java.sql.Connection.setAutoCommit(boolean autoCommit) is used to switch between the two modes. If a connection is in auto-commit mode, then all its SQL statements will be executed and committed as individual transactions. Otherwise, its SQL statements are grouped into transactions that are terminated by a call to either the method java.sql.Connection.commit or the method java.sql.Connection.rollback. By default, new connections are in auto-commit mode. After an application turns auto-commit off, a transaction is started. The transaction continues until either the java.sql.Connection.commit meothod, COMMIT [WORK] sql, the java.sql.Connection.rollback method, or ROLLBACK [WORK] sql is called; after that a new transaction is automatically started.

Calling the commit method ends the transaction. At that stage, HXTT XML checks whether the transaction is valid and raises an exception if a conflict is identified. If a conflict is encountered, your application should determine how to continue, for example whether to automatically retry the transaction or inform the user of the failure. A request to rollback a transaction causes HXTT XML to discard any changes made since the start of the transaction and to end the transaction.

    connection.setAutoCommit(false); // Explicit transaction handling
 
    Statement stmt = connection.createStatement();
 
    // Loop until transaction successful (or max retry exceeded)
    for(int count=0;; count++) {
        stmt.executeUpdate(yourSQL); 
        try{
            connection.commit(); // Commit transaction 
            break; 
        }catch(SQLException sqe) {
            // Check commit error
            if(sqe.getSQLState().equals("40000")) {
                //You can use sqle.getNextException() to know more information

                // Check number of times the transaction has been attempted
                if (count<3) {
                    continue;
                }
            }
            throw sqle;
        }
    }

Isolation Levels

An isolation level represents a particular locking strategy employed in the HXTT XML to improve data consistency. The higher the isolation level, the more locking or snapshot involved, and the more time users may spend waiting for data to be freed by another user. The isolation level provided by the HXTT XML determines whether a transaction will encounter the following behaviors in data consistency:

Isolation Levels and Data Consistency Definition

Isolation Level

Dirty Read

Non-repeatable Read

Phantom Read

None

Yes

Yes

Yes

Read uncommitted

Yes

Yes

Yes

Read committed

No

Yes

Yes

Repeatable read

No

No

Yes

Serializable

No

No

No

HXTT XML supports all isolation levels.

Performance Hints

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