Tips for table scan

A table scans access method guarantees that all of the rows in the table will be processed for the query. The main advantage of this access method is that the system is allowed to schedule the paging for the table in such a way as to minimize the total number of I/O's required to process all of the rows in the table. It accomplishes this task by requesting that larger portions of the table be paged asynchronously into main memory while the query is still processing.

This advantage of this more efficient scheduled paging is offset by the added cost to process all of the rows in the table. However, this can still be an efficient implementation when processing a larger percentage of the total rows in the table.

For more information, see Database Performance and Query Optimization in the Information Center Link to Information center.