Adaptive Server performs direct updates in a single pass:
It locates the affected index and data rows.
It writes the log records for the changes to the transaction log.
It makes the changes to the data pages and any affected index pages.
There are three techniques for performing direct updates:
Cheap direct updates
Expensive direct updates
Direct updates require less overhead than deferred updates and are generally faster, as they limit the number of log scans, reduce logging, save traversal of index B-trees (reducing lock contention), and save I/O because Adaptive Server does not have to refetch pages to perform modifications based on log records.