174 lines
6.9 KiB
Plaintext
174 lines
6.9 KiB
Plaintext
===============================
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LIVEJOURNAL'S TIME PROBLEM
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===============================
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Brad Fitzpatrick
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brad@livejournal.com
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August 10, 2000
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+------+
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| Goal |
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+------+
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LiveJournal.com needs to handle time better, in particular to be aware of time
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zones. There are too many problems that arise by neglecting them. If I knew of
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an easy solution, I'd have implemented it already. This document is a plea for
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help. All suggestions (however seemingly stupid) are likely to help, if only to
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spark ideas for others.
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Confession: I know very little about the details of time zones, daylight
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saving's time, etc... but I've read tons on the topic, enough to know there's
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a lot to know. In other words, the solution is likely complex as well.
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+---------------+
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| Current Setup |
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+---------------+
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LiveJournal's servers, and the primary developers are all on the west coast of
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the United States, in the PST/PDT (Pacific Standard/Daylight Time) timezone,
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which is -0800 GMT (and sometimes -0700 GMT, in daylight savings time, I
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believe). Here is how LiveJournal currently stores the dates/time for different
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events:
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* journal creation date, update date --- PST/PDT local time.
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* comment post dates --- PST/PDT local time.
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* journal entries:
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1) the "eventtime" is stored, whatever time you say it is wherever you're
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at. you specify the year, month, day, hour and minute. no time zone
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is recorded.
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2) the "logtime" ... the time LiveJournal logs it to the database, in
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PST/PDT local time.
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+-------------------------+
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| Description of problems |
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+-------------------------+
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Outlined below are the problems that LiveJournal currently faces:
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1. Friends view ordering
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2. Incorrect user clocks
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3. Offline journaling/queueing
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4. Comments post times
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1. Friends view ordering
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~~~~~~~~~~~~~~~~~~~~~~~~
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The friends view is currently sorted according to the "logtime". In other
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words, regardless of what time you said the journal event happened, the server
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will sort them in the reverse order they were received. This has the advantages
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that if you have friends scattered all over different timezones the journal
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entries will still show in the order they actually happened.
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The problem occurs though near midnight ... you can have friends in one
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timezone posting entries on one day interleaved with friends in another
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timezone posting commments on the previous day. The resultant friends view
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looks really messed up, going back and forth between days.
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This leads me to topic 2 ...
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2. Incorrect user clocks
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~~~~~~~~~~~~~~~~~~~~~~~~
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The friends view shows the time the user reported (the "eventtime"), even
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though it's sorted by the "logtime". So if a friend in your same timezone
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is posting comments near the same time as you, it's possible their post
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that happened after you has an earlier displayed time, because their computer
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clock is messed up.
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The worst is when their computer clock is months/years behind/ahead (very very
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common because Windows users like to double-click their clock and use it as
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a calendar ... then hit "OK" instead of "Cancel"). Then, the users complain
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that "my journal entries are showing up on my friends page, but not on my
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recent events view". This is because the recent events view (and the day
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view, and the calendar) are all sorted by the "eventtime", the time the user
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said the event happened.
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3. Offline journaling/queueing
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Many people have been asking for and patiently awaiting the "offline journaling"
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feature ... being able to enter journal entries on your no-Internet laptop or
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PDA and HotSync (or whatever) them later to LiveJournal's servers.
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Now, how should the friends view be formatted? Say the user submits 10 journal
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entries ranging over a two week vacation. Should all 10 show up at once on
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all of that user's friends' friends views? Because under the current scheme,
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the "logtime" of all those entries would be seconds apart, and that's what the
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friends view uses to sort.
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Should offline/queued entries not show up on friends lists? Should posts
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with eventtimes more than 'n' days in the past not show up on friends lists?
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Both those solutions suck, because they're both ugly hacks that avoid fixing the
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real problem -- adding timezone support to livejournal.
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4. Comment times
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~~~~~~~~~~~~~~~~
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Blah. You know the problem. Keep reading ... time for solutions:
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+----------------+
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| Ideal Solution |
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+----------------+
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Ideally what would happen is that LiveJournal would store all posts with a
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GMT time (that doesn't have daylight savings time) and the friends views
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would sort by the GMT time of the eventtime ... so the user that went on
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vacation and is dumping 10 entries into the system has them all intermixed
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with her friends' old entries. Then, the friends view should display both
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the remote browsing users's time and the time it was when the user posted the
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item.
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So the problem turns into -- how do we convert the "eventtime" the user
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submits into a GMT time? But ... let's assume the user's computer clock
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is wrong, or we don't want to use it because it's not perfectly synchronized.
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So then we need to pass along to LiveJournal a timezone field.
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So the problem is:
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--- I need a list of all timezones. What format are these in?
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When does daylight savings time occur? Each country and states
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within those countries have different rules.
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--- given a timezone code, how do I convert it to GMT? Are there
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good packages already in existence (preferrably in Perl) to
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do these conversions? I've looked around a lot, but haven't
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found anything perfect.
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--- how do we deal with legacy clients? it'll be some time
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before all clients start sending timezone info.
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Once the database is storing the eventtime in GMT and the timezone
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code as well, then the style system needs to be updated to allow style
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authors to show times in both the poster's time, and the journal owner
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or remote user's time.
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But perhaps there's a better solution? I really don't know. I hate the
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dependency on users' system clocks, and I hate the misordering of friends
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items.
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+----------------------+
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| Good example problem |
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+----------------------+
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I have a journal I wrote from 1990 that I typed up, but I don't want
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to post it, because it'll show up on all my friends' friends views. I'd
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prefer it just went to my calendar, and I can make a single post to tell
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my friends to go read it (and link to the day it starts).
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Sure, I could add a meta-data flag or something new on the protocol that
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says, "don't add this to my friends view" but then people will start using
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that for other purposes, and start asking for stupid stuff like, "can I have
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it not show up on certain people's friends view?", not understanding the
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point of it. It's just not clean. :/
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_____________________________________________________________________________
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Feedback requested:
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brad@livejournal.com
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