Re: Process balancing on smp db server/apache web server

Peter Darley sez:
} Friends,
}     I have been thinking about my smp db server and how it interacts
} with my web server.  I'm using mod_perl on Apache, which uses Apache::DBI
} to connect to the db server via a private network segment.  It occurs to
} me that since the web server is connecting early (on startup), when there
} is probably no load on the db server, the cpu that each backend is
} assigned to will be largely random, or, if there is a large syslogd
} operation or something right at that time, it might even put the majority
} of backends on the same processor.
}     When someone hits the web site it seems to me that there would be a
} greater than 50% chance that any two large queries from the web server
} would end up being run on the same processor.  Similarly, if I start a
} large processing script that uses the db, since the web associated
} backends are already assigned to a processor, there's a good (~50%?)
} chance that any big queries that come in through the web will be on the
} loaded cpu.
}     Does this make sense to anyone?  If this is true, are there any
} suggestions about how I can keep my persistent connections from Apache,
} while getting the db server to balance the load more efficiently?

In general, user processes don't have the option of locking themselves to
one CPU or another. Just because a process was started on one CPU does not
mean it will always be executed on it. Certain parts of the OS may demand
that they are only executed on a particular CPU for synchronization
purposes, but user-level processes use synchronization methods which
interact through memory with the CPU-locked OS code.

The short answer is that the OS does load balancing dynamically, and this
has nothing to do with on which CPU a process was spawned.

} Thanks,
} Peter Darley
--Greg