Updates to a database structure (such as by altering a
table, creating an index, or dropping an index) and modifications
to user authorization can change the access plan for the SQL statements
and affect performance.
About this task
In this procedure, before you change your database structure
or authorizations, you create and explain a query workload that contains
the SQL statements that are in your application. Then, you change
your database structure or authorizations. Finally, you create and
explain another query workload that contains the SQL statements in
your application, and compare the EXPLAIN snapshot for the first query
workload to the EXPLAIN snapshot for the second query workload.
Although
this procedure makes use of two separate query workloads, you can
create a single query workload, explain it, change your database structure
or authorizations, and then explain the query workload again. You
can then compare the two EXPLAIN snapshots.
To identify and address changes to access plans due to
changes to database structure or authorizations: