Date: Mon, 5 Jun 2006 13:35:32 -0400 From: John Nielsen <lists@jnielsen.net> To: stable@freebsd.org Subject: MySQL, ntpd, and kern.timecounter Message-ID: <200606051335.32838.lists@jnielsen.net>
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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? Can ntpd be coaxed into working with such bad timekeeping (as long as it's consistently bad)? 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? All input appreciated. Thanks! JN
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