Hi everyone, I just posted a note< http://blog.wikimedia.org/2011/11/18/nobody-notices-when-its-not-broken-new… 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. The project originally included recompressing all of the object types in the external store databases, continuing the work that was started in 2010. I spent some time doing verification that things were behaving as expected and it turns out they weren't. Upon examining the count of different data types in the external store content, I found that some types that are no longer supposed to be used were still getting created. I've filed https://bugzilla.wikimedia.org/show_bug.cgi?id=32478 to track the investigation and resolution of those differences. 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). 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. 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.) If there was a banner on all edit pages that informed the user not to save their document during a specific time period, they could choose to postpone the edit or finish quickly. The text would be something like "There will be planned maintenance starting in 23 minutes and lasting for 30 minutes. You will be unable to save edits during the maintenance period. Please save your work before maintenance begins." During the maintenance, we could change the message to be more visible, or we could take more drastic action such as disabling the edit or save buttons. 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'm sure there are some more ideas on what we should do, as well as opinions about these various options out there. Discuss! :) I haven't filed a bug yet, but will do so if this conversation comes to some consensus about a specific thing that should be done. Thanks, -ben _______________________________________________ Wikitech-l mailing list Wikitech-l(a)lists.wikimedia.org https://lists.wikimedia.org/mailman/listinfo/wikitech-l

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.

The project originally included recompressing all of the object types in the external store databases, continuing the work that was started in 2010.

I spent some time doing verification that things were behaving as expected and it turns out they weren't. Upon examining the count of different data types in the external store content, I found that some types that are no longer supposed to be used were still getting created. I've filed https://bugzilla.wikimedia.org/show_bug.cgi?id=32478 to track the investigation and resolution of those differences.

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:

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.

3) throw up a banner on the edit page itself. (...) During the maintenance, we could change the message to be more visible, or we could take more drastic action such as disabling the edit or save buttons.