1. Is there a way to model a process, such that process instances will not keep

From my experience, the answer to this question is no. The more processes the more memory needed. However you can minimise the effect by using sub-process and storing less data in the main process and archiving/deleting sub-process before the main process.

With the process instances the answer I believe is yes. We had a situation where a large number of processes were brought back from the archives and massively expanded our KDB's. They are now far larger than they were previously and despite re-archiving the processes there is no changes to our KDB's. From my understanding there is currently no way of compressing back the KDB's once expanded, they leave 'white space' in the file which keeps the file size. Normally I believe that the white space is used by new processes but worth remembering if you have a massive increase in the number of processes that your kdb’s will be expanded and maintain that size, until more processes are require.

Nikhil, there is no way to keep a process in the system without it occupying memory, so there is no way to have a process active in Appian (Active-Completed-Cancelled) without occupying some memory.

There are measures you can take to limit your memory foot print here:

forum.appian.com/.../Appian_Best_Practices

Reuse subprocesses and Define When to Keep, Delete, or Archive are good sections to review.

Thank you folks for the quick response!
A use case is such that the process has over 25 user input tasks with one of them recurring every alternate times (that user input task re occurs 12 times in the process). We thought of calling sub process for that task to improve the performance but fear that data will be lost once the sub process gets archived. Any suggestions on how to model process with tasks which are repeated multiple times throughout the process?

I am very concerned with this statement "With the process instances the answer I believe is yes. We had a situation where a large number of processes were brought back from the archives and massively expanded our KDB's. They are now far larger than they were previously and despite re-archiving the processes there is no changes to our KDB's. "

We need to unarchive processes or two model's. I am now concerned that if by doing this, it increases our KDBs so large that we can no longer import/inspect deploy packages. We already have a problem with this happening. Can someone from Appian explain exactly what is happening during the unarchive? Why does it leave "white space" in the file? Is there anything I can do to avoid this problem? Also, when I tested the unarchive script, I found that when I filter on the process start date, the command script fails. Why would that be happening? The script matches exactly the syntax of the instructions off your documentation.

any reason why the 'white space' cannot be trimmed? what it means is if my RAM utilization is 10 GB currently (due to KDB size) , even if we have archived processes later, the RAM utilization will never come down.