Avoiding locks during predicate evaluation
The EVALUATE UNCOMMITTED field of installation panel DSNTIP8 indicates if predicate evaluation can occur on uncommitted data of other transactions.
About this task
The option applies only to
stage 1 predicate processing that uses table access (table space scan,
index-to-data access, and RID list processing) for queries with isolation
level RS or CS.
Although this option influences whether predicate evaluation can occur on uncommitted data, it does not influence whether uncommitted data is returned to an application. Queries with isolation level RS or CS return only committed data. They never return the uncommitted data of other transactions, even if predicate evaluation occurs on such. If data satisfies the predicate during evaluation, the data is locked as needed, and the predicate is evaluated again as needed before the data is returned to the application.
A value of NO specifies that predicate evaluation occurs only on committed data (or on the uncommitted changes made by the application). NO ensures that all qualifying data is always included in the answer set.
- The query's access path
- The number of evaluated rows that do not satisfy the predicate
- The number of those rows that are on overflow pages
The default value for this field is NO.
Procedure
