What is a session?

[mkarp]

The proposed session generation method md5hex(sha256hex(device_id) + ":" + client_id + ":" + system_version + ":" + product_version) will produce new outputs only when a client application or the OS is updated.

I would assume that session is a period of time of a single usage of the client application. For example, user launches the app, uses it for a minute or two, and then closes it—this is a session. Next time user opens the app, it's a new session. This approach would produce chunks of events that will let us see what features, for example, should be optimised for quick usage.

I propose to append a :start_unix_timestamp to the session generation method.