Yes I’d be delighted to elaborate. I’m trying to chase down a puzzling anomaly. Quite likely I’m missing something obvious and feedback from the forum could save me from a wild goose chase.
The anomaly is in the ping data which I’ve been getting from my websites
(As I mentioned in another thread, I’ve been pinging since 2 of my websites were hit in January by the famous 30-second-delay-on-php bug which is still unsolved by DH afaik)
Except for a 2-day period in March (4th and 5th) when the bug returned (to another of my websites), all my sites have been consistently responsive, meaning that 99% of pings come back in less than 2 seconds.
The anomaly is in the distribution of the pings which fail to come back within 2 seconds: the data has puzzling spikes at 5 secs, 10 secs, 15 secs, 20 secs etc.
Considering only the ‘bad’ pings which fail to come back within 2 seconds, and omitting the data for March 4th and March 5th, here are the percentages (as a percentage of the bad pings) which come back within various intervals:
02 secs - 05 secs 32%
05 secs - 07 secs 52%
07 secs - 10 secs 3%
10 secs - 12 secs 4%
12 secs - 15 secs 1%
15 secs - 17 secs 7%
more than 17 secs 1%
(and yes, I am deliberately comparing intervals of 2 secs around the spikes with intervals of 3 secs between the spikes, just to show how skewed the data is).
(note also that the spike at 15 secs is much larger than the spike at 10 secs; in the raw data there are also visible spikes at 20 secs and 25 secs, but these are too small to be worth listing here).
Well, for all I know, this could be normal internet behaviour.
My first thought was that it could be something to do with TTL wraparound; maybe the extra work which the ping has to do when TTL expires involves some activity which has a natural granularity of 5 seconds.
So I added TTL data to the pings, and found that there seems to be no corellation at all between TTL expiry and badness of ping.
So I’m puzzled. I thought I’d better try to reproduce this behaviour on my other host before taking it further. Hence this thread.
Probably I should give some more detail in order to explain the issue better. The pings are all of the form
running as one of my users on a Dreamhost server, where $1 ranges over my websites and $2 varies over a few simple tests such as static html (“hello world”), minimal php (“hello world”), or some minimal sql activity (mysql_connect followed by mysql_select_db).
The spikiness of the timing data looks slightly different when php (or php with sql) is invoked but basically the figures are approximately as above whether or not php/sql are involved.