Effect of member configuration on access path selection

Because plans and packages are bound on individual members in the group, the way a member is configured influences the access path chosen for statements in that plan or package.

For example, it is possible to have different buffer pool sizes and different RID (record identifier) pool sizes on each member. It is also possible that members are on different CPC models.

When you bind your application from one of the members, Db2 chooses the best access path, given the catalog statistics, CPC model and buffer pool sizes, among other things. Suppose, though, that the selected access path is optimal for the one member, but is a relatively poor choice for a different member in the same group. Because the group shares the catalog and directory, the same plan (and hence the same access paths) are used regardless of member, after the application is bound.

Where to bind in a mixed data sharing configuration: If your data sharing group consists of mixed CPC models, be aware that the speed of a central processor might change your access path. This effect is more likely to occur with long-running queries than with fast-running transactions.

Automatic rebind: The access path can change if automatic rebind occurs while the application is executing on a different member than the one on which the original bind occurred.