Hi everyone,
I just posted a
note<http://blog.wikimedia.org/2011/11/18/nobody-notices-when-its-not-br…
the blog about our new external store but wanted to add a few details
here. The deploy went smoothly, and I'm very happy with how the project
progressed overall. There are plenty more details on the project itself on
the project wiki
page<http://wikitech.wikimedia.org/view/External_storage/Update_2011-08&…
hiding in RT. there were a few followup things to come out of it, and
I want to talk through those in hopes that someone either picks them up or
has suggestions on what to do.
From what I've read on the blog, that sounds like a
"Good Work
everyone" is in order :)
During the deploy there was a brief (about 10 minute) period during which
article saves failed due to the external store databases being in read-only
mode. As expected, some folks showed up in IRC telling us of the
'problem'. After the migration was complete we brainstormed a bit in IRC
about good ways of informing editors of planned maintenance such as this
migration. The regular databases (s3, etc.) have a read-only mode flag so
that the affected wikis show a reasonable error, but the external store
databases are a little different. Because of the way they're spread out,
the outage of a specific database cluster does not affect specific language
projects, but instead affects a specific time range for all wikis.
Additionally, the currently writable external store database affects
article edits on all wikis.
There were a few suggestions thrown around:
1) use central notice. This would certainly have the effect of alerting
all wikis that there was some maintenance, but it has the disadvantage of
telling all *readers* about the outage, rather than only the people that
would actually be interested (those editing pages).
--^ Seems to be the most reasonable thing to do. Readers who don't
care, probably don't read sitenotices that don't involve giant
pictures of everyone's favourite Wikipedia founder, and even if they
do read it, I'm sure they'd ignore it. A small maintenance notice is
not likely to annoy people. Saves not working is likely to annoy
people. Saves not working after you spent an hour revising whatever
article you're writing will definitely frustrate people.
2) make mediawiki cache the change to conceal the
outage from editors. The
idea here is that mediawiki would notice that the backend database is
currently in read-only mode and would cache the change and write it to the
DB when it returns to read-write mode. There are a number of technical
challenges here, as well as the introduction of another system (the change
cache), but it's an interesting way around the problem, since rather than
addressing how to inform editors of impending maintenance it simply
eliminates the necessity for that communication.
Sounds (very) needlessly complex. Not to mention if it partially fails
and people edits go through, then un-go through, people won't be
happy.
3) throw up a banner on the edit page itself. The
time when we want to
inform someone that there is going to be maintenance that will impede
editing is when the user begins an edit. (at the moment we inform them
when they try to save the edit in the form of an error message.)
[..]
This also sounds reasonable. I personally would just go with just a
normal central notice, but this would also be fine imo.
4) don't make any change from what we do now. The
external store databases
rarely fail or undergo maintenance. Increasing the complexity of the
system to protect against their outage will be more likely cause harm than
the outages themselves. Instead, just announce it on the blog before and
apologize to anybody affected afterwards.
I really feel that having a site/central notice for planned
maintenance is important. At the very least stuff like this should
probably be announced on various mailing lists or VP's. Our editors
are important, we should make sure we avoid unnecessarily wasting any
time/effort they put in to the wiki.
-bawolff