It's a bit complicated. When SRE sets the read-only mark, they start counting from that time and it starts propagating which takes a while to be actually shown to all users but some users might still see the RO error while some actual writes are happening somewhere else because the cache is not invalidated yet (I think it has a TTL of 5 seconds but I need to double check). We still consider that as RO time because it's affecting users regardless.
HTH
Am Mi., 1. März 2023 um 18:06 Uhr schrieb Dušan Kreheľ < dusankrehel@gmail.com>:
Clément Goubert and everybody,
I analyzed https://stream.wikimedia.org/v2/stream/recentchange and i have the another results.
Last change (before migration): 2023-03-01T14:00:30 First change (after migration): 2023-03-01T14:02:05 Result: Down time (14:00:31 to 14:02:05) is 94s.
I think that analysis is more authoritative. I think it analyzes based on something like REQUEST_TIME in PHP.
Dušan Kreheľ
2023-03-01 16:30 GMT+01:00, Clément Goubert cgoubert@wikimedia.org:
Dear Wikitechians,
Dear colleagues,
The switchover process requires a *brief read-only period for all Foundation-hosted wikis*, which started at *14:00 UTC on Wednesday March 1st*, and lasted *119 seconds*. All our public and private wikis
continued
to be available for reading as usual. Users saw a notification of the upcoming maintenance, and anyone still editing was asked to try again in
a
few minutes.
As a side note, with other SREs we have been trying to discern the effect of the Switchover in many of the graphs we have to monitor the infrastructure in https://grafana.wikimedia.org during Switchover. In
many,
it's impossible to tell the event. The most discernible graph we have is
of
the edit rate, which can be viewed here: Grafana <
https://grafana-rw.wikimedia.org/d/000000208/edit-count?from=1677673800000&a...
. Can you spot it? See the attached picture to help:
I am extending thanks to everyone that was also present on IRC, helping
out
in any way that they could. Thanks as well to Community Relations who notified communities of the read-only window ahead of time. And thanks to everyone that contributed to MultiDC https://wikitech.wikimedia.org/wiki/Performance/Multi-DC_MediaWiki, especially Performance for pushing forward with the last parts of it, allowing us to perform this Switchover faster and with more confidence
than
ever before.
If you wanna relive through the Switchover, here's a link to a capture of Listen to Wikipedia https://en.wikipedia.org/wiki/Listen_to_Wikipedia during
the
Switchover: Listen to the Switchover <
https://drive.google.com/file/d/1jqQUVCq3ksjOM5bKoIfCZ5Zt9RRW1Nl_/view?usp=s...
(spoiler: the part with no sounds is the switchover)
A similar event will follow a few weeks later, when we move back to Virginia. This is currently scheduled for *Wednesday, April 26th*. Thank you,
On Tue, Feb 21, 2023 at 1:55 PM Clément Goubert cgoubert@wikimedia.org wrote:
Dear Wikitechians,
I would like to remind you that the datacenter switchover will happen on *Wednesday March 1st* starting at *14:00 UTC.*
Please refer to the original email for any additional information. As always, you can reach out to me directly or the SRE team in #wikimedia-sre on IRC with any question, or through Phabricator.
Thank you,
On Tue, Feb 14, 2023 at 1:58 PM Clément Goubert <cgoubert@wikimedia.org
wrote:
Dear Wikitechians,
On *Wednesday March 1st*, the SRE team will run a planned data center switchover, moving all wikis from our primary data center in Virginia
to
the secondary data center in Texas. This is an important periodic test of our tools and procedures, to ensure the wikis will continue to be available even in the event of major technical issues in our primary home. It
also
gives all our SRE and ops teams a chance to do maintenance and upgrades on systems in Virginia that normally run 24 hours a day.
The switchover process requires a *brief read-only period for all Foundation-hosted wikis*, which will start at *14:00 UTC on Wednesday March 1st*, and will last for a few minutes while we execute the migration as efficiently as possible. All our public and private wikis will be continuously available for reading as usual, but no one will be able to save edits during the process. Users will see a notification of the upcoming maintenance, and anyone still editing will be asked to try again in a few minutes.
CommRel has already begun notifying communities of the read-only
window.
A similar event will follow a few weeks later, when we move back to Virginia. This is currently scheduled for *Wednesday, April 26th*.
If you like, you can follow along on the day in the public #wikimedia-operations channel on IRC (instructions for joining here https://meta.wikimedia.org/wiki/IRC/Instructions). To report any issues, you can reach us in #wikimedia-sre on IRC, or file a
Phabricator
ticket with the *datacenter-switchover* tag (pre-filled form here <
https://phabricator.wikimedia.org/maniphest/task/edit/form/1/?projects=Datac...
);
we'll be monitoring closely for reports of trouble during and after the switchover. (If you're new to Phab, there's more information at Phabricator/Help.) The switchover and its preparation are tracked tracked in Phabricator Task T327920 https://phabricator.wikimedia.org/T327920
On behalf of the SRE team, please excuse the disruption, and our thanks to everyone in a number of departments who've been involved in planning this work for the past weeks. Feel free to reply directly to me with
any
questions.
Thank you,
-- Clément Goubert (they/them) Senior SRE Wikimedia Foundation
-- Clément Goubert (they/them) Senior SRE Wikimedia Foundation
-- Clément Goubert (they/them) Senior SRE Wikimedia Foundation
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