Does anyone know what the easiest and most cost-efficient method would be to che

One way can be Use the Execute process Report Smart Service on a report (containing all the valid process Ids) and save it in a long array now check whether your ids (used in SS) does exists in the new array or not.

Can you explain what your use case is? Where would you get the invalid id's from? Is this related to archived processes?

An interesting idea about using the report but that seems excessive. Is there some sort of low cost function I can call and possibly catch on InvalidProcessException? If it generates that exception, then I know the process doesn't exist.

And to answer your question Sathya, user error.

Another way can be When the actual instance is created, you would be saving data to a external db. Here you can also save the process instance id. Now you just have use a query to check whether that particular (that you wanna check) exists or not.

Why are users dealing with process Id? Can you explain a bit more on this?

We have users that manually create csv documents with job ids in them. Since it is done manually, there is the potential for human error. We had to implement our system this way in order to give our users the desired functionality.

yes, Sathya's point is correct. If you want user to have some unique identifier for his/her process instance create a sequence generator for each request of particular process. That way user fill feel more friendly to use the application and may decrease chances of error. Though you can always design to crosscheck.

Ok. Few things to keep in mind. Mixing user activity with process identifier could lead to challenges that you've just mentioned. Especially if users need to refer to a very long number and retype in a CSv file.

If you must associate the two, then you should consider having a process that does this for the end user, thus avoiding manual intervention.

Having said that, your option is to use the analytic smart service ootb or processanalytis API call which actually does the same in the background.

Finally, I can't emphasize the importance of getting your architecture right from day 1 so you have great processes.....