The CONCURRENT_UPDATES option specifies that a table modify is to be performed online. Unlike a regular modify, which locks out all other access to the table for the entire duration, an online modify permits normal read and update access to the table for most of the modify.

When the online modify completes, however, exclusive access to the table is still required during a brief period to apply any updates that were made to the table during the online modify. The length of this period depends on the number of updates that must be applied.

Online modification of tables cannot be accomplished in the following: