June 10, 2011 I found an interesting quote in the Oracle
Database documentation library: “Row Locks (TX) A row lock, also
called a TX lock, is a lock on a single row of a table. A
transaction acquires a row lock for each row modified by one of
the following statements: INSERT, UPDATE, DELETE, MERGE, and
SELECT … FOR UPDATE. The row lock exists until the transaction
commits or rolls back. When a transaction obtains a row lock for
a row, the transaction also acquires a table lock for the table
in which the row resides. The table lock prevents conflicting
DDL operations that would override data changes in a current
transaction. Table Locks (TM) A transaction automatically
acquires a table lock (TM lock) when a table is modified with
the following statements: INSERT, UPDATE, DELETE, MERGE, and
SELECT … FOR UPDATE. These DML operations require table locks to
reserve DML access to the table on behalf of a transaction and
to prevent DDL operations that would conflict with the
transaction. You can explicitly obtain a