标签：set cut back and ever required statement object data
A data definition language (DDL) statement is either nonblocking or blocking, and both types of DDL statements require exclusive locks on internal structures. If these locks are unavailable when a DDL statement runs, then nonblocking and blocking DDL statements behave differently:
Nonblocking DDL waits until every concurrent DML transaction that references the object affected by the DDL either commits or rolls back.
Blocking DDL fails, though it might have succeeded if it had been executed subseconds later when the locks become available.
To enable blocking DDL statements to wait for locks, specify a DDL lock timeout—the number of seconds a DDL command waits for its required locks before failing.
To specify a DDL lock timeout, use the DDL_LOCK_TIMEOUT parameter. The permissible range of values for DDL_LOCK_TIMEOUT is 0 to 1,000,000. The default is 0. You can set DDL_LOCK_TIMEOUT at the system level, or at the session level with an ALTER SESSION statement.
Specifying the DDL Lock Timeout
标签：set cut back and ever required statement object data
原文地址：http://www.cnblogs.com/shulin-peng/p/7686975.html
