Refine the logic for recording the nominal sent age of the mail
In the previous iteration, if we were ever down/frozen/disabled long enough
to miss sending two mails in a row, we would see unintended "catch-up"
behavior where each subsequent run of britney would send a mail until the
right total number of mails had been sent. Don't do this; instead, catch us
up in one go to the most recent mail that should have been sent, avoiding
bunching of notifications.
We were checkpointing after each email was sent to ensure that an aborted
p-m run didn't result in double emails; however, because the new cache only
contains records for packages we've seen so far during this run (to avoid
the cache growing without bounds over time), that means an aborted p-m run
*still* throws away records for all packages still waiting to be processed.
To fix this, we:
- only checkpoint records of writing emails during this in-progress run to
a temp file
- check for this temp file on britney startup, and if present, merge the
results into the current state
- move this temp file into the final cache location only at the end of the
britney run
Along the way, fix up a bug introduced in the previous commit that would have
us only saving state for those packages for which we sent email during the
current run, which would have quite bad effects.
Rework the email frequency calculation to account for gaps in runs
The previous code had some issues with respect to how we decided whether to
send an email. The age used for calculating when the next mail should be
sent was saved as a float rather than an integer; since p-m runs never
happen exactly an integer number of days after upload, this results in a
cumulative error in the timing of the emails, that is further exacerbated if
a particular run is significantly delayed or if p-m infrastructure is down
for a period of time.
So instead, we now calculate the age at which the most recent email /should
have been sent/, and store that in our cache instead of the precise age.
There is still a bit of surprising behavior here due to the fact that we use
two different 'max_age' values for valid vs. invalid candidate packages: a
single package can, over the course of its stay in -proposed, move from
being an invalid candidate to being a valid candidate /and back again/
without ever migrating. Such a package will switch back and forth between
two sets of calculations based on different starting offsets, causing the
ages at which the emails are sent to vary in a non-obvious fashion.
However, this will still obey the general principle of "email reminders of
decreasing frequency", so I think this is acceptable given that it is still
an overall improvement in predictability.
Merged
into
~ubuntu-release/britney/+git/britney2-ubuntu:master
at
revision 132ffaf4653523ca5f05e1ffbc64ed61d48c3f1f
