Specifying the DDL Lock Timeout

You can specify the amount of time that blocking DDL statements wait for locks.

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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.

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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.

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• To specify a DDL lock timeout, set 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.

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