Re: Add session statistics to pg_stat_database

On Fri, 2020-12-04 at 16:55 +0100, I wrote:
> > > Basically, that would change pgStatSessionDisconnectedNormally into instead being an
> > > enum of reasons, which could be normal disconnect, abnormal disconnect and admin.
> > > And we'd track all those three as separate numbers in the stats file, meaning we could
> > > then calculate the crash by subtracting all three from the total number of sessions?
> > 
> > I think at least "closed by admin" might be interesting; I'll have a look.
> > I don't think we have to specifically count "closed by normal disconnect", because
> > that should be the rule and could be more or less deduced from the other numbers
> > (with the uncertainty mentioned above).
> 
> I am considering the cases
> 
> 1) client just went away (currently "aborted")
> 2) death by FATAL error
> 3) killed by the administrator (or shutdown)

I think I figured it out.  Here is a patch along these lines.

I named the three counters "sessions_client_eof", "sessions_fatal" and
"sessions_killed", but I am not wedded to these bike shed colors.

Yours,
Laurenz Albe