[SalesForce] Linking CronTrigger sObjects to Scheduled Jobs listings

You have hit a DML limit. While the algorithm you mention is correct:

if you created a class like this and scheduled it to run once a day it would update everyone in the loop, which would then be picked up by a workflow I have in there

You're not taking into account Salesforce limits. You're limited to manipulating only up to 10000 records in one execution context. If you have more than 10000 contacts in your org, you will get the exception you mention above. Read more about limits here: https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_gov_limits.htm

In your case, the best way to overcome this limitation is to use your scheduled job to trigger a batch Apex job: https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_batch_interface.htm

It turns out there was some sort of Salesforce bug. I was able to repeat the issue at will.

Here's the situatuon: I was scheduling a job from a scheduled job. However, because sometimes I have seen scheduled jobs get significantly delayed in their execution, even to the point where it doesn't execute until it's fire time is in the past (which throws "System.AsyncException: Based on configured schedule, the given trigger will never fire."), I used a try catch block, with first system.schedule inside the try braces.

It turns out, when there is in fact such an AsyncException that gets caught, the apex job somehow is scheduled in spite of the caught exception. The obvious problem is however that it's scheduled for a past time that will never be reached. As a result, it hangs indefinitely in the apex jobs queue, but for some reason does not have a corresponding scheduled job to delete, and of course the scheduled class is locked from updating until this is resolved. Feels like a bug to me.

I was able to resolve it by simply copying and deleting the schedulable class, which in turn deleted all corresponding apex jobs (including those which had completed, aborted, etc.). I was then able to easily re-create the class by pasting back in the code.

Instead of using a try catch block, I am now using if statements to compare the scheduled run time with datetime.now(), and if the run time is in the past, I increment it by minutes at a time in a while loop until it becomes later than now. Then the job gets scheduled with the incremented run time.