On Wed, Oct 14, 2009 at 08:43:25PM -0700, Ask Bjjjrn Hansen wrote: > On Oct 14, 2009, at 19:44, der Mouse wrote: > >Lest anyone think otherwise, this is not hypothetical. > > Graphs from carefully chosen[1] DNS servers in the pool.ntp.org > infrastructure shows a bit over twice as many queries over the minutes > around the top of the hour as any other similar time interval. I'm > sure if the graph was granular down to seconds it'd be much more > extreme.
I've been collecting data as well and there are patterns everywhere. The on-the-hour spike starts about a second before the hour with the majority of clients hitting my server between 1.12 seconds and 3.31 seconds after the hour. It slowly tails off till about 9 second when it's reached normal levels. At its highest point it's about 4 times normal activity. Looking further over the hour it's still interesting; there are spikes every minute that are ~20% above normal with especially big spikes at 30 minutes (300% above normal and much more concentrated than the one on the hour) and every 10 minute interval (150% above normal) and 5 minute interval (80% above normal). Note that that's above, so 300% above = 4 times. All fun and seems to suggest that people are pretty crap at picking when to request the time. Then again, if we look at the amount of traffic that actually occurs within these "busy" periods it's less than 5% of everything else. If I try and correct this 5% to take account of the baseline activity that would be occurring if everybody was picking the best times then I see 2% (depending on how I do it) of the overall traffic in these spikes. Even assuming a worst case of 5% I'd say that most people most of the time (i.e. 95%) do a very good job of picking when to request time. So, to those people who want to use a cron job. I'd say go for it, just make sure it's not too close to the hour, the minute isn't divisible by 5 and you put a random pause in (up to a second, as I see very reliable spikes at 370ms to 400ms into each second) and you should be set. -- Sam http://samason.me.uk/ p.s. plots available if people are interested _______________________________________________ timekeepers mailing list [email protected] https://fortytwo.ch/mailman/cgi-bin/listinfo/timekeepers
