Performance

The Performance Check asks whether your target answers slower than you want. It sends no requests of its own: it reads the times the Uptime Check’s runs already measured.

Answer time

Answer time is how long a run waited for the first sign of an answer:

• Website and API: until the first byte of the answer arrived.
• TCP: until the connection was made.
• Ping: until the reply came back.

The Runs tab shows each run’s Answer time, and the parts it was made of.

The median across your locations

After each run of the Uptime Check, the Performance Check takes the newest run from each of the Monitor’s locations, if that run came within the last 2 Intervals and got an answer. It then reads the median of their Answer times: the middle one, or, for an even number of locations, the lower of the two middle times. So one distant location that is slow never warns on its own.

When no location got an answer, there is no Answer time to judge, and the Performance Check keeps the status it had. A target that does not answer is down, not slow, and the Uptime Check tells you that.

Your threshold

You set the threshold when you create or edit the Monitor. Unless you choose another, it is 2 seconds. It can be anything from 50 milliseconds to 30 seconds.

When the median is over the threshold, the Check’s status is warning. Otherwise it is ok. The Performance Check never fails, so it never opens an Incident and never counts against your uptime.

What a warning says

A slowness warning names the part of the request that got slower: looking up the name, the connection, the secure connection, or waiting for the answer. For a Ping Monitor, the parts are looking up the name and the reply. For example:

Waiting for the answer got slower: 2.0 s, up from its usual 0.2 s.

“Usual” is each location’s own Usual time: the median of its runs over the 7 days before the warning started. A location needs at least 10 runs in that time to have one. When no location has a Usual time, or the answer did not get slower than usual, the warning says which part of the time was largest instead.

The threshold is still yours: the Usual time explains a warning, and never raises one.

When a slowness warning arrives

A warning is said once. While the median stays over the threshold, or moves back and forth across it, you hear nothing more. It ends once the Check has been ok for 20 minutes.

It arrives in a digest 5 minutes after the first warning, so several Monitors that turn slow together reach you as one message.