showplan messages provide information about whether an update is performed in direct mode or deferred mode. If a direct update is not possible, Adaptive Server updates the data row in deferred mode. There are times when the optimizer cannot know whether a direct update or a deferred update will be performed, so two showplan messages are provided:
The “deferred_varcol” message shows that the update may change the length of the row because a variable-length column is being updated. If the updated row fits on the page, the update is performed in direct mode; if the update does not fit on the page, the update is performed in deferred mode.
The “deferred_index” message indicates that the changes to the data pages and the deletes to the index pages are performed in direct mode, but the inserts to the index pages are performed in deferred mode.
These types of direct updates depend on information that is available only at runtime, since the page actually has to be fetched and examined to determine whether the row fits on the page.