supermirror pull frequency should be more transparent

[David Allouche]

The page for a mirror branch should display the following information:

"This is a mirror branch it is updated every <pull interval>. The next mirroring will occur approximately at <time rounded up to the higher 10 mins>."

Use case: vila merged a critical bug into bzr.dev, and then merged an urgent fix. The branch was mirrored between the bug and its fix. Vila is anxious to know why his bugfix has not been mirrored yet.

[Zygmunt Krynicki (zyga)]

The page mirror branch should also display information about last failed mirroring attempt.

[Robert Collins (lifeless)]

it already shows data about failed mirroring attempts when the last attempt was a failure.

I think a reasonable UI would be:
for non-hosted branches:
 'next mirror: 7 hours away' and
 'last mirrored: 17 hours ago'

and given that hosted branches have better granularity, and for consistency, it might be nice on hosted branches to show:
 'next mirror: automatic on push' and
 'last mirrored: 23 days ago'

[Tim Penhey (thumper)]

This isn't really a fix-it-friday bug.

In order to implement this properly we should use the mirror_request_time for mirrored branches as well. At the moment the mirror_request_time is used as a flag by the sftp server to say that the hosted branch is ready to pull. We should use this column as a timestamp and check for mirror_request_time < UTC_NOW. This way the branch puller script could update this timestamp for mirrored branches with the next pull time. Once that is set we can then display the next mirror time.

With that field also enabled in that way, it allows a fairly trivial implementation of a "Mirror ASAP" button for mirrored branches, and also a way to implement the exponential back off for failed mirrors.

[Jonathan Lange (jml)]

The branch that fixes this just missed out on getting into trunk before the code freeze.

[Jonathan Lange (jml)]

RF 4777