On Sun, Apr 4, 2021, at 09:16, Fabien COELHO wrote: > If other cases are indeed pointers. For pgbench, all direct "if (xxx &&" > cases are simple booleans or integers, pointers seem to have "!= NULL". > While looking quickly at the grep output, ISTM that most obvious pointers > have "!= NULL" and other cases often look like booleans: > > catalog/pg_operator.c: if (isDelete && t->oprcom == baseId) > catalog/toasting.c: if (check && lockmode != AccessExclusiveLock) > commands/async.c: if (amRegisteredListener && listenChannels == NIL) > commands/explain.c: if (es->analyze && es->timing) > … > > I'm sure there are exceptions, but ISTM that the local style is "!= NULL".
Many thanks for explaining. > > >> I'm wondering whether it should be possible to designate (1) a file the > >> content of which would be shown, or (2) a command, the output of which > >> would be shown [ok, there might be security implications on this one]. > > > > Can't we just do that via plpgsql and EXECUTE somehow? > > Hmmm. > > Should we want to execute forcibly some PL/pgSQL on any new connection? Oh, of course, you want the command to be execute for each new connection. My idea was to use PL/pgSQL to execute only when you wanted to update the stored motd value, but of course, if you want a new value from the command for each new connection, then that doesn't work (and it doesn't work anyway due to not being able to execute ALTER SYSTEM from functions). > Not sure this is really desirable. I was thinking of something more > trivial, like the "motd" directeve could designate a file instead of the > message itself. > > There could be a hook system to execute some user code on new connections > and other events. It could be a new kind of event trigger, eg with > connection_start, connection_end… That could be nice for other purposes, > i.e. auditing. Now, event triggers are not global, they work inside a > database, which would suggest that if extended a new connection event > would be fired per database connection, not just once per connection. Not > sure it would be a bad thing. Such a hook sounds like a good idea. If we would have such a hook, then another possibility would be to implement motd as an extension, right? /Joel
