Re: proposal: psql: psql variable BACKEND_PID

Hi,

On 2023-02-13 18:06:23 +0100, Peter Eisentraut wrote:
> On 09.02.23 10:11, Pavel Stehule wrote:
> > first and main (for me) - I can use psql variables tab complete - just
> > :B<tab> - it is significantly faster
> > second - I can see all connection related information by \set
> > third - there is not hook on reconnect in psql - so if you implement
> > BACKEND_PID by self, you ensure to run query with pg_backend_pid() after
> > any reconnect or connection change.
> >
> > It is clean so you can run "select pg_backend_pid() AS "BACKEND_PID"
> > \gset" and you can store it to .psqlrc. But most of the time I am in
> > customer's environment, and I have the time, possibility to do a
> > complete setup of .psqlrc. It looks (for me) like a generally useful
> > feature to be everywhere.
>
> But what do you need the backend PID for in the first place?

For me it's using gdb, pidstat, strace, perf, ...

But for those %p in the PROMPTs is more useful.

> Of course, you might want to use it to find your own session in
> pg_stat_activity or something like that, but then you're already in a query
> and can use pg_backend_pid(). What do you need the backend PID for outside
> of such a query?

E.g. I fire of a query, it's slower than I'd like, I want to attach perf. Of
course I can establish a separate connection, query pg_stat_activity there,
and then perf. But that requires manually filtering pg_stat_activity to find
the query.

Greetings,

Andres Freund