process model nodes

The maximum number of nodes between two user input tasks is 50 including those two User Input Task

for which purpose? If for activity chaining then 50.

Let's be clear, You can have as many nodes as you like, but there are consequences for doing so hence the best practices and the warnings that Appian will raise.

If you have > 50 nodes in a chain, Appian will break the chain for you, so you synchronous experience will be broken at that point. The process will continue to run in the background. Any User Input Tasks after the break will be assigned as Tasks to the User.

Depending on the volume of concurrent instances of very large process models in memory you may experience performance impacts due to memory "stress". Bets practice therefore recommends you keep process models small, and set your Archiving/Deletion settings to remove completed instances from memory as soon as possible. How soon depends on your local requirements.

Try and conduct as much processing as you can in Expression rules to reduce the number of nodes you have in a process model. This is best practice not just for addressing the above issues but also makes it easier to conduct testing as you can test the Expression Rules in isolation and only plug them into your process model when you are confident they do exactly as intended.

Also break up a large process model into smaller sub-process. Often (not always though) you can create re-usable sub-processes which means your delivery will have a lower maintenance overhead a repeated code is reduced.