John Nielsen <[EMAIL PROTECTED]> writes: > I have a FreeBSD 6.1 machine set up as a web and MySQL database server. Since > the application is a bit database-intensive, I followed several of the MySQL > tuning recommendations from this page: > > http://wikitest.freebsd.org/MySQL > > One of those was to change kern.timecounter.choice from ACPI-fast to TSC. > > That was fine for MySQL, but the real-world timekeeping on this hardware with > TSC is so bad that it broke ntpd and the clock started drifting several > seconds every hour. Timekeeping with ACPI-fast was quite reliable. > > I'm looking for recommendations in general, but I'll pose a few specific > questions below as well. > > Should I change the timecounter back? How big an impact does the choice of > timecounter have on performance with MySQL 4.1.19 and FreeBSD 6.1? Is there a > conservative way I can answer this question myself for a server that's > already in production?
Benchmarking on a live system is tough. You can switch the timecounter back and forth easily enough, but measuring performance requires a predictable load. I don't know anything about mysql in particular, but on a fast machine, with the database as the primary application, I wouldn't expect choice of clock tick to affect the performance very much. > Can ntpd be coaxed into working with such bad timekeeping (as long as it's > consistently bad)? You're not using a driftfile? That should compensate for systematic drift pretty well. You just specify the file (which ntpd has to be able to write) in the configuration file for ntpd (/etc/ntp.conf by default). > Would Bad Things happen if I ran ntpdate or ntpd -q once or twice a day? > Would > this be considered an abuse of the ntp server(s)? Would I run a risk of > confusing / breaking cron or sendmail or syslogd or anything else with the > time jumps? Nothing horrible would happen, but it could be annoying. I'd recommend you avoid it. _______________________________________________ [email protected] mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-stable To unsubscribe, send any mail to "[EMAIL PROTECTED]"
