Re: Performance monitor signal handler

Philip Warner wrote:
> At 13:49 16/03/01 -0500, Jan Wieck wrote:
> >
> > Similar problem as with shared memory - size. If a long
> > running backend of a multithousand table database needs to
> > send access stats per table - and had accessed them all up to
> > now - it'll be alot of wasted bandwidth.
>
> Not if you only send totals for individual counters when they change; some
> stats may never be resynced, but for the most part it will work. Also, does
> Unix allow interrupts to occur as a result of data arrivibg in a pipe? If
> so, how about:
>
> - All backends to do *blocking* IO to collector.

The general problem remains. We only have one central
collector with a limited receive capacity. The more load is
on the machine, the smaller it's capacity gets. The more
complex the DB schemas get and the more load is on the
system, the more interesting accurate statistics get. Both
factors are contraproductive. More complex schema means more
tables and thus bigger messages. More load means more
messages. Having good statistics on a toy system while they
get worse for a web backend server that's really under
pressure is braindead from the start.

We don't want the backends to block, so that they can do
THEIR work. That's to process queries, nothing else.

Pipes seem to be inappropriate because their buffer is
limited to 4K on Linux and most BSD flavours. Message queues
are too because they are limited to 2K on most BSD's. So only
sockets remain.

If we have multiple processes that try to receive from the
UDP socket, condense the received packets into summary
messages and send them to the central collector, this might
solve the problem.

Jan

--

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