Each application with embedded SQL statements must have a CA Datacom/DB access plan. The plan contains information required by CA Datacom/DB about your program and information about each SQL statement you have embedded. The plan is built when you submit your application to CA Datacom/DB's SQL Preprocessor. The Preprocessor has options which you can either specify or let default to determine how the Preprocessor processes the SQL statements and controls certain aspects of the application's environment.
One of the SQL Preprocessor options (ISOLEVEL=) specifies the isolation level, meaning the degree to which a unit of recovery in your application is isolated from updating operations (such as SQL statements INSERT, UPDATE, or DELETE) or other units of recovery.
A unit of recovery is defined as the data and control information needed to enable CA Datacom/DB to back out or reapply all of an application's changes to recoverable resources since the last commit point.
In the following pages of this chapter, when a reference is made to ISOLEVEL=C, be aware that the implication is, that in the context of the particular situation being described, ISOLEVEL= cannot be specified as U. This is because ISOLEVEL=U does not acquire locks or allow changes, but other ISOLEVEL= specifications do, as shown in the following list.
Specifies that no locks are acquired and no changes are allowed.
Specifies that locks are acquired and changes are allowed.
Specifies "repeatable read," in which locks are acquired and restricted changes are allowed.
Note: For detailed information about isolation levels and using SQL, see the CA Datacom/DB SQL User Guide.
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