Using the Product in a DB2 Environment › Explain Function › Information on the Explain Panel

Information on the Explain Panel

You can find out additional information about Explain and how its output can help you make performance evaluations of a particular SQL statement in the IBM® manual, DB2 Application Programming and SQL Guide. A partial list of the key issues you should attempt to resolve for long-running or often-used SQL is shown next.

Index matching did not work

An index was available for the table that was accessed, but no matching columns were found.

This situation is often a result of a difference in the length of the data item in the program and the length of the column in the DB2 table.

Not using Sequential Prefetch

Sequential Prefetch reads multiple pages of a table into the buffer pool with a single I/O operation.

This situation significantly reduces delays for SQL access when large amounts of data are accessed.

Not using List Prefetch

List Prefetch is a way of accessing data pages efficiently.

List Prefetch can be used in conjunction with either single or multiple index access.

Not specifying parallel operations

Parallel operations specify that pages of a partitioned table might be prefetched by using multiple I/O streams.

This solution improves access significantly.