Applications of Batch Apex

Like any feature of Force.com, Batch Apex works best when you apply it to an appropriate use case that meshes well with its unique capabilities. The following list provides some guidelines when evaluating Batch Apex for your project:

Single database object—Batch Apex is optimized to source its data from a single, “tall” (containing many records) database object. It cannot read data from other sources, such as callouts to Web services. If the records you need to process span many database objects that cannot be reached via parent-child or child-parent relationships from a single database object, you should proceed carefully. You will need to develop separate Batch Apex code for every database object. Although this is doable and you can share code between them, it creates maintenance headaches and quickly exposes you to the limitation of five active batch jobs per organization.

Simple scope of work—Although Batch Apex allows the use of custom code to provide it with the records to process, it is most powerful when the scope of work is expressed in a single SOQL statement. Do some work up front to ensure that the source of data for your batch can be summed up in that single SOQL statement.

Minimal shared state—The best design for a Batch Apex process is one where every unit of work is independent, meaning it does not require information to be shared with other units of work. Although creating stateful Batch Apex is possible, it is a less mature feature and more difficult to debug than its stateless counterpart. If you need shared state to be maintained across units of work, try to use the database itself rather than variables in your Apex class.

Limited transactionality—If your batch process is a single, all-or-nothing transaction, Batch Apex is only going to get you halfway there. You will need to write extra code to compensate for failures and roll back the database to its original state.

Not time-critical—Salesforce provides no hard guarantees about when Batch Apex is executed or its performance. If you have an application that has time-based requirements such that users will be prevented from doing their jobs if a batch does not run or complete by a specific time, Batch Apex might not be a good fit. A better fit is a process that must run within a time window on the order of hours rather than minutes.

These guidelines might seem stifling at first glance, but Batch Apex actually enables an impressive breadth of interesting applications to be developed that were previously impossible with other forms of Apex.