Re: Performance monitor signal handler

* Tom Lane <tgl@sss.pgh.pa.us> [010316 10:06] wrote:
> Jan Wieck <JanWieck@Yahoo.com> writes:
> >     Uh - not much time to spend if the statistics should at least
> >     be  half  accurate. And it would become worse in SMP systems.
> >     So that was a nifty idea, but I think it'd  cause  much  more
> >     statistic losses than I assumed at first.
> 
> >     Back to drawing board. Maybe a SYS-V message queue can serve?
> 
> That would be the same as a pipe: backends would block if the collector
> stopped accepting data.  I do like the "auto discard" aspect of this
> UDP-socket approach.
> 
> I think Philip had the right idea: each backend should send totals,
> not deltas, in its messages.  Then, it doesn't matter (much) if the
> collector loses some messages --- that just means that sometimes it
> has a slightly out-of-date idea about how much work some backends have
> done.  It should be easy to design the software so that that just makes
> a small, transient error in the currently displayed statistics.

MSGSND(3)              FreeBSD Library Functions Manual              MSGSND(3)


ERRORS
     msgsnd() will fail if:

     [EAGAIN]           There was no space for this message either on the
                        queue, or in the whole system, and IPC_NOWAIT was set
                        in msgflg.

-- 
-Alfred Perlstein - [bright@wintelcom.net|alfred@freebsd.org]