For the next two examples, imagine that an Apex trigger has been created for the Contestant object and an Apex class has been written to implement some logic to update the contestants' championship points depending on their position when the race ends.

In the first example, the Contestant record is updated directly from the UI and the Apex Debug log shown in the next screenshot is captured.

Notice the EXECUTION_STARTED and EXECUTION_FINISHED lines; these show the actual start and end of the request on the Salesforce server. The CODE_UNIT_STARTED lines show where the platform invokes Apex code. Also, note that the line number shows EXTERNAL, indicating the platform's internal code called the Apex code. For the sake of brevity, the rest of the execution of the code is collapsed in the screenshot:

In this second example, imagine that some Apex code was executed to calculate the contestants' championship points once the race ends. In this case, the code was executed from an Execute Anonymous prompt (though in the application, this would be a button); again, the Apex Debug log was captured and is shown in the next screenshot.

Again, you can see the EXECUTION_STARTED and EXECUTION_FINISHED entries, along with the three CODE_UNIT_STARTED entries—one for the RaceService.awardChampionshipPoints Apex method called from the Execute Anonymous prompt and two others for the Apex Trigger code:

What is different from the first example is, which you can see by looking at the Line column, that the execution transitions show the lines of the Apex code being executed and EXTERNAL. When DML statements are executed in Apex to update the Contestants records, the Apex code execution pauses while the platform code takes over to update the records. During this process, the platform eventually then invokes Apex Triggers and once again, the execution flows back into Apex code.

Essentially, the execution context is used to wrap a request to the Salesforce server; it can be a mix of the execution of the Apex code, Validation Rules, workflow rules, trigger code, and other logic executions. The platform handles the overall orchestration of this for you. The Salesforce Developer Console tool offers some excellent additional insight into the time spent on each of these areas. The following screenshot shows an example of this view:

If the subscriber org has added Apex Triggers to your objects, these are executed in the same execution context. If any of these Apex code units throw unhandled exceptions, the entire execution context is stopped and all database updates performed are rolled back, which is discussed in more detail later in this chapter.