fixes https://github.com/TryGhost/Team/issues/2562
New event fetching loops:
- Reworked the analytics fetching algorithm. Instead of starting again
where we stopped during the last fetching minus 30 minutes, we now just
continue where we stopped. But with ms precision (because no longer
database dependent after first fetch), and we stop at NOW - 1 minute to
reduce chance of missing events.
- Apart from that, a missing fetching loop is introduced. This fetches
events that are older than 30 minutes, and just processes all events a
second time to make sure we didn't skip any because of storage delays in
the Mailgun API.
- A new scheduled fetching loop, that allows us to schedule between a
given start/end date (currently only persisted in memory, so stops after
a reboot)
UI and endpoint changes:
- New UI to show the state of the analytics 'loops'
- New endpoint to request the analytics loop status
- New endpoint to schedule analytics
- New endpoint to cancel scheduled analytics
- Some number formatting improvements, and introduction of 'opened'
count in debug screen
- Live reload of data in the debug screen
Other changes:
- This also improves the support for maxEvents. We can now stop a
fetching loop after x events without worrying about lost events. This is
used to reduce the fetched events in the missing and scheduled event
loop (e.g. when the main one is fetching lots of events, we skip the
other loops).
- Prevents fetching the same events over and over again if no new events
come in (because we always started at the same begin timestamp). The
code increases the begin timestamp with 1 second if it is safe to do so,
to prevent the API from returning the same events over and over again.
- Some optimisations in handing the processing results (less merges to
reduce CPU usage in cases we have lots of events).
Testing:
- You can test with lots of events using the new mailgun mocking server
(Toolbox repo `scripts/mailgun-mock-server`). This can also simulate
events that are only returned after x minutes because of storage delays.
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