A side effect is by definition some mutation that's out of the scope of the function -- if the purpose of the microservice is to put stuff in a database, then (by definition) it's not a side effect. Switching a flag on top of doing some work, on the other hand (e.g. flip "processed" to true in a global database) is a side effect.
Modifying data in a database is a side effect. Since you brought up the wikipedia definition, here it is:
> In computer science, a function or expression is said to have a side effect if it modifies some state outside its scope or has an observable interaction with its calling functions or the outside world besides returning a value. For example, a particular function might modify a global variable or static variable, modify one of its arguments, raise an exception, write data to a display or file, read data, or call other side-effecting functions.
Note "write data to a display or file". I think we agree that writing to a database falls under this definition, hence using terms like "side effecting" when talking about microservices is misleading.
Technically it depends on if anything outside the service can see the database and if the state is saved after the service returns. It might seem useless to call a DB if you're not going to save state, but a Rube Goldberg architecture could do so for the lulz.
