Each poll of a host's overview graph held a worker for one second between
two CPU samples. The answer now carries its sample, signed with the time
and the compute; the next poll sends it back and the usage is taken since
then, so a point is the average since the previous one (normally 5 s, at
most 15 s). Without a sample, or with one that is altered, older or from
another host, or when the host restarted, it is measured over one second
as before.
A sample is one reading; the busy share was mixed from separate readings,
counted guest time twice (it is part of user) and added half a percent.
A host that cannot be read leaves a gap in both graphs instead of a zero
CPU point and a broken memory axis.
The VM page polls the VM state every 5 s and, while its Stats tab is
open, the statistics every 10 s; the compute overview polls the host
graph every 5 s. All used setInterval:
- A new request went out on schedule while the previous one was still
open. When a host goes silent, a stats request waits up to 30-45 s,
so each open page held several sync workers at once.
- Each time the Stats tab was shown, the page made new charts and a
new interval without stopping the old ones, and polling went on on
the other tabs of the page.
- Hidden pages kept polling at full rate.
Measured in a browser against a test server (old code / new): Stats tab
shown 4 times, 31 s on it: 12 / 2 requests; 31 s on another tab of the
page: 12 / 0; page hidden for 31 s: 15 / 0, and the new code asks once
right after the page is shown again; with 25 s answers, at most 15 / 1
requests open at once.
static/js/poll.js repeats a request while the page is visible: the
next one 5 or 10 s after the previous answer, none while hidden, one at
once when shown again. The Stats tab makes its charts once and polls
only while shown. The answer handler runs after the poller's own
bookkeeping, so an error in it (a chart for a disk added meanwhile)
does not stop the polling. A Node test of poll.js runs with the test
suite when node is installed.
