The Signpost

Technology report

With the 1.19 deployment now (mostly) complete, developers consider possible "mini" deployment later in the month

MediaWiki 1.19 deployment complete: well, almost

Caching is vital if Wikimedia servers are to avoid being overloaded. The data shows, however, that the deployment of 1.19 caused a sharp, hopefully temporary drop in the percentage of requests handled by the parser cache (the green line).

Over a period of several hours spread across 29 February and 1 March, MediaWiki 1.19 went live to all remaining Wikimedia wikis including the English Wikipedia. Although a number of problems were reported, the deployment as a whole only had to be reverted on the handful of wikis, such as Serbian and Chinese, which rely on the MediaWiki software to provide the same content in two scripts automatically (wikitech-l mailing list). As of time of writing, zhwikis and srwiki are still awaiting the fix that would allow the deployment to proceed.[update 1]

Perhaps more worryingly, the jump in the amount of traffic handled by 1.19 from approximately 10% of total traffic to a figure approaching 100% does appear to have put a significant strain on the Wikimedia servers. Specifically, system administrators have noted a sharp decline (pictured right) in the parser cache hit rate – the percentage of requests for web pages that could be handled without a need for further processing – around the time of the 1.19 deployments. System administrators will be hoping that the effect is only temporary; although its appearance is not yet fully understood, the latest data does indicate that the rate is slowly retreating back to its previous average.

In addition to working on the bug reports that flood in after virtually all large deployments (of which some 23 are currently marked as requiring a fix before 1.19 is released to external sites), developers have also been looking afresh at the issue of changing the default diff colouring (first covered in the Signpost back in December). MediaWiki 1.19 had headlined with accessibility improvements in this area, the benefits of which seemed to have ensured that the change survived a series of long discussions when it was first proposed. On the change's final deployment, however, observers noted that decreases in the contrast ratio offset the improvement for colour-blind users, forcing the change to be reverted (wikitech-l mailing list). A third design is now being trialled; nevertheless, the bold blue-and-yellow-bordered design is almost certain to provoke a fresh round of discussions which it will have to survive if it is to make it onto Wikimedia wikis.

Updates

  1. ^ Shortly after publication, the deployment of a temporary fix allowed the Chinese and Serbian Wikipedias to be updated to 1.19.

Git switchover delayed; schedule for rest of month established

Lack of server capacity was among the reasons given by WMF director Rob Lanphier this week as he explained why the Git switchover had to be postponed.

The Git switchover, which had been been scheduled for March 3, has been postponed until March 21 (wikitech-l mailing list). Announcing the decision on behalf of the Foundation, WMF director of platform engineering Rob Lanphier cited a number of factors, including the unexpected scale of the difficulties resulting from the 1.19 deployment, along with software and hardware issues that would take time to resolve. Perhaps more worryingly, there also seem to be signs that a new code review backlog (the bane of the WMF deployment team's life over the past two years) is starting to build, and that too will need to be resolved before the Git switchover if all the revisions made are to be brought across.

The delay establishes a preliminary schedule for the rest of the month, to include heavy doses of code review, resolution of the hardware and software issues holding back the switchover, a MediaWiki 1.19 release candidate, the full MediaWiki 1.19.0 release, and possibly (if resources permit) a further "mini" deployment to Wikimedia wikis of the sort which will become increasingly common after the Git switchover. Lanphier, however, was clear that the successful Git switchover remained the key objective. "Anything that distracts from that (like, for instance, a [further Wikimedia] deploy) may get postponed while we finish this off once and for all". As of time of writing, Git repositories covering core code and WMF-deployed extensions are currently in a preparatory "read-only" mode, with write-actions for the existing Subversion repository being automatically fed into them (wikitech-l mailing list).

In brief

An example of an OpenStreetMap map of the kind now in use on social networking site Foursquare

Not all fixes may have gone live to WMF sites at the time of writing; some may not be scheduled to go live for many weeks.


















Wikipedia:Wikipedia Signpost/2012-03-05/Technology_report