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Re: Server-side hooks for user session start and session end

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2015-09-26 18:17 GMT+02:00 Nikolai Zhubr <n-a-zhubr@xxxxxxxxx>:
Hi all,

I'm trying to find a soultion to automatically execute something (preferrably a function or at least some pure sql statements) at the beginning and at the end of a user session. As an example, imagine just storing of all login and logout timestamps (though the real task is a bit more complicated than that)

I would not like it to be somehow explicitely client-side initiated (like e.g. trivially calling some certain do_at_sess_begin(), do_at_sess_end()) because first, a malicious client could then mess it up easily, and furthermore, in the case that the session somehow ended abnormally (due to say temporary network fault) client-side finalizer function would not be called anyway.

My first try was to create an event trigger for sql drop events, then create a temporary table and watch for its drop at the end of a session. However, it seems drop events are just not fired for temporary tables (although documentation does not state this anywhere, as far as I can see, maybe I'm wrong about that)

It would seem like one of the simplest things ever, but I'm now totally stuck out of ideas.

As a partial solution, handling just session _end_ would already be OK. 

Any thoughts?

This cannot be solved without patching PostgreSQL source code :( . There are not good hooks for custom extension. Patch is relative simple, but I cannot to publish it.

You have to modify main loop in src/backend/tcop/postgres.c file. Login point can be immediately before loop. Logout point can be joined to  'X',EOF message.

Attention - there are some corner case, what are necessary to solve - mainly how to handle exceptions in login/logout procedures.

Regards

Pavel

p.s. I understand so this hack is necessary for porting older application from other databases, but I am not sure if it is a good idea to use it. Not all tasks can be solved well in database. 
 


Thank you,
Nikolai


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