About DML Lockings

When automatic data manipulation language (DML) is used in Oracle Application Express to update or delete rows of a table, a transaction is initiated to first lock the row, verify if it has changed since it was displayed on the page, and then finally issue the actual UPDATE or DELETE statement for the row.

In some environments where locking of rows is prevalent, you may wish to control the DML operation and determine if the DML operation:

waits indefinitely
fails immediately
waits for a specified period of time

You can set the value of an application substitution string, an application item, or a page item named APEX_DML_LOCK_WAIT_TIME to control this operation. The following values are supported:

If null (the default), results in the same behavior as previous versions of Oracle Application Express, that is, wait indefinitely.
If 0, fail immediately if the row is locked by another database session.
If > 0 and the row is locked, wait for the specified number of seconds.

When set in an application, the value for APEX_DML_LOCK_WAIT_TIME applies to all UPDATE and DELETE DML operations using Automatic DML in the entire application. To control a specific Automatic DML process, update the value of APEX_DML_LOCK_WAIT_TIME before the Automatic DML process and reset it after the Automatic DML process. Note that this does not affect updates and deletes using tabular forms.