ORA-54 While Alter Index Unusable Online

刘泽宇

现象：
Received below error when alter an index unusable online:

alter index <Index_name> unusable online;

ORA-00054: resource busy and acquire with NOWAIT specified or timeout expired

原因：
The error is expected if DML operations for the underlying object are not completed within the specified DDL_LOCK_TIMEOUT value:

ONLINE Clause is a new enhancement introduced in 12C to make index UNUSABLE, ALTER INDEX UNUSABLE ONLINE will not impact ongoing DML. DDL operations can wait for a user configurable time period (DDL_LOCK_TIMEOUT), if underlying resource is busy, and is supported at system and session levels.

处理方法：

It executes successfully if no ongoing DML operations.