It is becoming increasingly common for both companies and individuals to monitor the uptime (availability) of their websites and servers. That way they can be notified of problems as soon as they occur and also view how their site has performed historically.
However, not all monitoring is created equal. How useful uptime monitoring will be to you depends greatly on the monitoring resolution you are using.
What is monitoring resolution?
When you set up monitoring, most uptime monitoring services will let you select a monitoring resolution, which usually ranges from one to 60 minutes. This is the interval at which your site will be checked. For example, a monitoring resolution of 5 minutes means that a site will be tested once every 5 minutes.
The problem with low-resolution monitoring
The problem with low-resolution monitoring is the same you have when viewing a low-resolution picture. It will not be a good likeness to the original. It is logical: The more often you check something, the more likely you are to catch any irregularities and the more exact the measurement will be.
Above: The difference in detected downtime between different monitoring resolutions (green is up, red is down). Note that in this case, only the 1-minute monitoring is able to detect all the downtime intervals and also has a much more accurate summary of total downtime during the measured period.
As you can see in the picture, even with a 5-minute monitoring resolution the detected downtime can differ significantly from the actual downtime, and the problem increases the lower your monitoring resolution becomes. It is easy to see that the higher the monitoring resolution, the closer you get to the real downtime.
Another problem to take into account is that if you check your websites less frequently, you run the risk of completely missing downtime. If a website is checked every minute, the longest downtime you can miss is just under one minute. With a 60-minute resolution, you can miss up to an hour of downtime if you have bad luck with the timing of the checks (and when it comes to running a website, don’t count on luck).
Higher resolution, higher cost?
Yes, most uptime monitoring services charge more for a higher monitoring resolution (we don’t, though, pardon the plug), but if you care about having accurate uptime statistics and want correct and immediate notifications for when downtime starts and ends, you really should choose a 1-minute monitoring resolution.