Extension:NavigationTiming

MediaWiki extensions manual

NavigationTiming Release status: stable
Implementation	Ajax
Description	Logs perceived latency measurements from client-side
Author(s)	Patrick Reilly, Ori Livneh, Asher Feldman, Timo Tijhof, Ian Marlier
Compatibility policy	release branches
Database changes	No
License	GNU General Public License 2.0 or later
Download	Download extension Git [?]: Download Git master browse repository (GitHub) commit history code review README
Parameters $wgNavigationTimingSamplingFactor
Hooks used BeforePageDisplay ResourceLoaderGetConfigVars
Translate the NavigationTiming extension if it is available at translatewiki.net
Check usage and version matrix.
Issues	Open tasks · Report a bug

The NavigationTiming extension allows logging perceived latency measurements, exposed by browsers as part of the W3C Navigation Timing spec, which "defines an interface for web applications to access timing information related to navigation and elements".

Scope

Browsers accounting for upto 5% of Wikimedia traffic (as of November 2017) may not be included in the results due these browsers not supporting Grade A for MediaWiki and/or the Navigation Timing API. See also https://caniuse.com/nav-timing.

How is the information used?

Engineers at Wikimedia Foundation intend to use this data to assess the impact (positive and negative) of changes to code or server configuration, and thus to help guide ongoing work on site performance.

Sample configuration

wfLoadExtension( 'EventLogging' ); // required dependency
wfLoadExtension( 'NavigationTiming' );
$wgNavigationTimingSamplingFactor = 10;  // log 1:10 requests.
$wgNavigationTimingOversampleFactor = [
    'geo' => [
        'US' => 5
    ],
    'userAgent' => [
        'Chrome' => 100
    ]
];

Oversampling

Oversampling allows us to selectively sample a larger portion of the traffic coming from a particular geography, or with a specific User Agent string in the browser. Use cases for this include: getting detailed observations of the change in performance based on factors like data center location; or evaluating the change in performance due to things like browser upgrades (eg, the release of Firefox 57, which had significant rewrites that were intended to improve performance).

Oversampling is configured using the wgNavigationTimingOversampleFactor variable. This variable is an associative array, and the keys that are checked are "geo" and "userAgent".

If the user's country code is included in the 'geo' array, then a sample is taken with frequency 1/samplerate. If the user's browser has a User Agent string that matches a key in the userAgent array, then a sample is taken with frequency 1/samplerate. No more than 1 oversample is taken for a given request.

If the request is oversampled, the emitted event will include these properties:

• isOversample: true
• oversampleReason: string, whose contents are a JSON array of reasons that the oversample happened. These will be of the form "geo:XX" (where XX is the country code that matched), or "ua:ABCDEF" (where ABCDEF is the string that was found in the browser's User Agent string)

Further reading

About the data we collect:

• Explainer of navtiming metrics, Wikitech.
• See the NavigationTiming schema for the data format (transported using EventLogging).

• Wikimedia Performance Portal: Data from Navigation Timing, performance.wikimedia.org.
• Wikimedia Graphs: Navigation Timing dashboard, grafana.wikimedia.org

About the Navigation Timing API in web browsers:

• Navigation Timing API, specification from the W3C.
• Annotated Timing object: simplified descriptions of the measurements.
• Measuring Page Load Speed with Navigation Timing, HTML5 Rocks.

Code stewardship

• Maintained by Performance Team.
• Issue tracker: Phabricator (Report an issue)