Salesforce is committed to ensuring that the interactive user experience (browser or mobile response times) of your applications and that of its own is as optimal as possible. In a multitenant environment, it uses the governors as one way to manage this. The other approach is to provide a means for you to move the processing of code from the foreground (interactive) into the background (async mode). This section of the chapter discusses the design considerations, implementation options, and benefits available in this context.

As the code running in the background is, by definition, not holding up the response times of the pages the users are using, Salesforce can and does throttle when and how often async processes execute, depending on the load on the servers at the time. For this reason, it currently does not provide an SLA on exactly when an async piece of code will run or guarantee exactly when the Apex Scheduler code will run at the allotted time. This aspect of the platform can, at times, be a source of frustration for end users, waiting for critical business processes to complete. However, there are some design, implementation, user interface, and messaging considerations that can make a big difference in terms of managing their expectations.

The good news is that the platform rewards you for running your code in async by giving you increased governors in areas such as heap, SOQL queries, and CPU governor. You can find the full details in their documentation (attempting to document them in a book is a nonstarter as they are constantly being improved and removed in some cases).