Posted: Feb 22, 2008
by Billy Gray
Tagged pingme
Suppose you have something really important to do every week, like checking that your car is still legal for street cleaning (raise your hand if you’ve been towed). You’d probably be tempted to set up a ping that both repeats and pesters. This way you’d get pestered about it each day to make sure that you don’t forget, and PingMe would reschedule it for next week once you completed the task.
In the past, this feature has been missing from PingMe. When you received a pestering ping that also has a repeat schedule, and you replied with ‘off’ or ‘done’ or ‘stop’ (or ‘ok’ or ‘okay’) to stop the pester, say from your phone, the ping would be marked as done, and it would turn off. For good. But most people really set pester & repeat pings up so that after they turn off the pester for today, they’ll still get the ping tomorrow (or whenever the next scheduled repeat is, if you follow me).
Well now you have options! We’ve changed the behavior of two of the stop words so that they only stop the pester of a ping and not the repeat. As of this morning, replying to a ping with ‘ok’, ‘okay’ or ‘done’ will stop only the pester of a pestering & repeating ping. Replying with ‘stop’ or ‘off’ will turn the ping off as before.
To sum it up, once you go and move your car to the other side of the street, you can reply to the ping ‘ok’ and it will stop bothering you until tomorrow, when it’s time to move your car again.
==> /var/log/pingme/PingMeReceiver.log <==
[INFO] change: 17827, Preparing
[INFO] change: 17827, stripping message part 0...
[INFO] change: 17827, Processing.
[INFO] change: 17827, found a stop message on this line: Ok
[INFO] change: 17827, this is a stop message for ping 16427,
[INFO] change: 17827, user requests to stop pester
[INFO] change: 17827, nagging and recurring ping, clearing events for reschedule
It’s alive!
Posted: Feb 08, 2008
by Billy Gray
Tagged pingme, rails
Over at Ryan’s Scraps, in a post about the new TimeWithZone functionality in edge Rails, there are a pair of comments that I want to highlight. A fella named Ben asks “Couldn’t this be pushed deeper so that current_user.registered_at is a TimeWithZone?”
Then there’s a response from the main guy who developed the TimeWithZone functionality, Geoff Buesig, in regards to how they intend it to be used (and with a bunch of other neat and helpful notes that you should check out):
1.TimeWithZone is similar to the Duration class, in that, you should never need to create an instance directly—in the TWZ case, you’ve got the #in_time_zone, #in_current_time_zone, #change_time_zone and #change_time_zone_to_current methods on Time and DateTime instances that will handle that for you.
So, for example, you can do this:
current_user.registered_at.in_current_time_zone
… and the result will automatically be wrapped in a TimeWithZone
What Ben is asking for, and what Geoff seems to be distancing himself from, is exactly what we here at Zetetic would find incredibly useful: the ability to harness our database backend’s time zone support, PostgreSQL’s ‘timestamp with time zone’.
Here’s the deal. PingMe was designed for users around the globe so it supports time zones. We set it up so that all timestamps (:datetime) were stored in UTC in the database, and converted to the user’s local time on display. We also convert from the user’s local time on datetime input. Nothing fancy or unexpected there, really. And hey, the tzinfo gem supports DST, so we’re good, right?
Well, PingMe is a scheduling system. It has a scheduler daemon that’s constantly checking to see which pings need to be sent out, then it creates outbound events for the dispatcher daemons to deliver. Never mind the terminology, the important thing here is that it’s working in UTC. And that Rails is storing the timestamps in Postgres’ default TIMESTAMP WITHOUT TIME ZONE data type. Here’s an illustrative query:
def lock_a_block(type_name)
before = (Time.now.utc).to_s(:db)
ActiveRecord::Base.connection.execute(
<<-END_OF_SQL
UPDATE events SET dispatcher = '#{@name}'
WHERE id IN (
SELECT e.id FROM
(( events e INNER JOIN targets t ON e.target_id = t.id )
INNER JOIN pings p ON e.ping_id = p.id)
INNER JOIN target_types tt ON t.target_type_id = tt.id
WHERE
tt.const = '#{type_name}'
AND
(
(e.dt_when < '#{before}' AND e.status = '#{Event::STATUS_PENDING}')
OR
(e.retry_at < '#{before}' AND e.status = '#{Event::STATUS_RETRY}')
)
AND e.dispatcher IS NULL
AND t.activated_at IS NOT NULL
AND (p.is_done = 'f' OR p.is_done IS NULL)
AND (p.deleted_at IS NULL)
ORDER BY
e.dt_when ASC
LIMIT #{@block_size}
);
END_OF_SQL
)
end
So the app is providing a UTC timestamp for the before variable, and the timestamps are in UTC in the database. What happens when DST begins or ends? Nothing changes. Everything is sent at the set time, for UTC. So a ping set for 5pm EST was stored at 12:00 UTC, and when 5pm shifts an hour for EDT, that ping is still stored at 12:00 UTC and will be sent either an hour early or an hour late, depending on the circumstance.
The only way we could break this up to work off the time zone setting on the user model is to execute separate queries for all of our users all the time joining against their timezone. Ridiculous! And following Geoff’s notion of things above, it’s just not a clean solution — storing the ping’s time without the time zone is decidedly inaccurate. I hate to say it.
I think the best solution is not to store in UTC here, but to store as a timestamp with time zone. I realize that sounds like an impure solution, but it’s not: PostgreSQL actually stores the data in UTC and can do all sorts of magical conversions for us. We could still use the code above and work in proper UTC, but any DST on the timezone would be respected:
WHERE ... e.dt_when AT TIME ZONE 'UTC' < '#{before}'
And that is why I hope Geoff changes his mind, because we do need TimeWithZone as a data type in Rails, or perhaps a col definition that will provide a TimeWithZone instead of Time objects:
col.datetime :col_name, :with_time_zone => true
As an aside, we don’t leave PingMe users to hang when DST rolls around, we update the relevant time stamps via SQL. But I would like to get us to a better solution. Being able to store TimeWithZone would do just the thing.
