Adaptive Server uses deferred updates when direct update conditions are not met. A deferred update is the slowest type of update.
In a deferred update, Adaptive Server:
Locates the affected data rows, writing the log records for deferred delete and insert of the data pages as rows are located.
Reads the log records for the transaction and performs the deletes on the data pages and any affected index rows.
Reads the log records a second time, and performs all inserts on the data pages, and inserts any affected index rows.