Pl sql trigger if updating

Of course, the rows of the table are not locked forever.When sessions perform commit the locks on those rows are released, but before that unlock period gets very far, other sessions may update some other rows of the table—and thus the slice of time to get the exclusive lock on the table vanishes.

Finally, you will learn how to manage database tables such as creating new a table or modifying an existing table’s structure.Jill the DBA at Acme Retailers is trying to alter the table called SALES to add a column, TAX_CODE.It's pretty routine stuff; she issues the following SQL statement: The error message says it all: the table is being used right now, probably by a transaction, so getting an exclusive lock on the table may be next to impossible.Updating 400 million rows will not only take a very long time, it will also fill up the undo segments, generate a large amount of redo, and create massive performance overhead.So Jill has to ask for a "quiet period"—an outage—to make this change.

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