Suppose there is system for gathering info about system activities. There is a client part with an interface and there are agent parts that are installed on each machine. I estimate that there could be max 20 computers now. Later could be more like 50.

My solutions:

1. Agent stores data into local database e.g. sqlite. There is also a service which can be used by a client to query data. So if a client wants to display data for 50 computers, he sends a query to 50 computers. I'am on that solution now but maybe it's totally wrong.

2. Agent stores data into local database (I don't known good one for that). There is also server (main database) and local databases are synchronized with the server. In this case, a client connects to the main database to display data.

3. Agent sends data in realtime to main database. So same as point 2, but there is no sync.

4. Like in point 3, but agent buffers data in local database and sends it in small chunks to main database.

What is the best approach?