How and what do you log in your projects?

Question

PHP

I am writing a more or less serious project, I need to log any user action and, in general, everything that happens in the system. I want to know how you log and what do you log in your projects? Where do you store it in the database or in files?

Answer 1

Login, logout (date, time, IP),
Active actions that cause data changes
queries in case of using search
and the system is not a very clear moment, depending on what kind of project you have.
And to store in basis or files depends on the project. In the case of a simple log for admins, a simpler file. In the case of subsequent use of the log for statistics, or at least if it should be viewed by several people (for example, even one, but not a system administrator), you can even make reports in BD to view logs according to certain criteria

Answer 2

If the project is highload, then it is initially written to a file (definitely not to the database), and then collected and sorted into the database by the collector.

Answer 3

Logging is necessary for you to search for unauthorized access and system errors. Therefore, you need to log into the log:
Everything else is for curiosity.