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.
LP: #1671468
Steve Langasek
27ef44e478