What is Queueable Apex?
Queueable Apex was first introduced in the Winter '15 Salesforce release, that was some time around the end of 2014. It was delivered as a response to the growing use of both Batch Apex and future methods and developers finding use cases where neither was an ideal solution. This led to the development of Queueable Apex. Queueable Apex allows a developer to submit a job for processing and then at the end of that job, start another job, chaining multiple jobs together, something like this:
Figure 9.1 – Jobs are chained together with each job
From Figure 9.1, we see that each chained job is invoking another job, in the process, if needed until the full process is complete. Perhaps the best way to understand Queueable Apex is to understand the original reason it was designed. In his detailed blog post (https://developer.salesforce.com/blogs/engineering/2014/10/new-apex-queueable-interface.html), Josh Kaplan from the Salesforce...