Re: Tracking wait event for latches

On Wed, Sep 21, 2016 at 10:23 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> I have to admit that I like the individual event names quite a bit,
> and I think the detail will be useful to users. But I wonder if
> there's a better way to describe the class of events that we're
> talking about that's not so dependent on internal data structures.
> Maybe we could divide these waits into a couple of categories - e.g.
> "Socket", "Timeout", "Process" - and then divide these detailed wait
> events among those classes.

pgstat.h is mentioning that there is 1 byte still free. I did not
notice that until a couple of minutes ago. There are 2 bytes used for
the event ID, and 1 byte for the class ID, but there are 4 bytes
available. Perhaps we could use this extra byte to store this extra
status information, then use it for WaitEventSet to build up a string
that will be stored in classId field? For example if a process is
waiting on a socket and a timeout, we'd write "Socket,Timeout" as a
text field.

> The "SecureRead" and "SecureWrite" wait events are going to be
> confusing, because the connection isn't necessarily secure. I think
> those should be called "ClientRead" and "ClientWrite".
> Comprehensibility is more important than absolute consistency with the
> C function names.

Noted.

> Another thing to think about is that there's no way to actually see
> wait event information for a number of the processes which this patch
> instruments, because they don't appear in pg_stat_activity.

We could create a new system to track the activity of system-related
processes, for example pg_stat_system_activity, or pg_system_activity,
and list all the processes that are not counted in max_connections...
--
Michael