Express Hints gives DB2 DBAs and Application programmers the ability to manipulate the PLAN_TABLE settings that influence the access path choices for a given SQL Statement.
Express Hints makes it a simple matter to generate the correct PLAN_TABLE entry to direct DB2 to a desired access path. It then verifies the validity of the selected access path without forcing the user to actually bind the plan or package.
Express Hints gives DB2 DBAs and Application programmers the ability to manipulate the PLAN_TABLE settings that influence the access path choices for a given SQL Statement.
Express Hints makes it a simple matter to generate the correct PLAN_TABLE entry to direct DB2 to a desired access path. It then verifies the validity of the selected access path without forcing the user to actually bind the plan or package.
DB2 V6 introduced the Optimization Hint feature. This facility allows the user to override the DB2 optimizer's choice of access path. As implemented, however, the feature requires the user to manually update the PLAN_TABLE and then rebind the plan or package just to determine if the desired access path is even valid.
Using Optimization Hints is difficult due to the skill level required to perform the table updates, as well as the inherently error-prone nature of the process. Even the most experienced DBA's may not recall each of the many parameter settings that need to be changed. The number of Application Programmers possessing the requisite skill is even less. Plus, the only method provided for validating a hint is to do an actual bind!
Express Hints resolves these problems. Using a straightforward ISPF dialog, the programmer or DBA selects the Plan or Package from a PLAN_TABLE. The individual SQL statements are then displayed. The user selects an SQL statement and is shown the current access path from the PLAN_TABLE. Various options are offered for changing the access path. When one of the changes is selected, it is then verified to see whether it is acceptable to DB2 before the Hint is actually added to the PLAN_TABLE.
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