---------- Forwarded message --------- From: Jason Linehan jlinehan@wikimedia.org Date: Wed, Feb 19, 2020 at 4:12 PM If your team uses mw.user.sessionId() for instrumentation, a recent change to MediaWiki could impact your numbers.

The new patch https://gerrit.wikimedia.org/r/#/c/mediawiki/core/+/572011/ changes the way that session IDs work, bringing their behavior closer to other platforms that many of us are familiar with.

The value returned from mw.user.sessionId() will now:

- be the same in different tabs of the same browser process - be the same in different windows of the same browser process - be forgotten once the browser process ends

Since 2017, values returned from mw.user.sessionId() have only been constant within the same browser tab, and only lasted until the tab was closed. This had gone unnoticed until recently. See T223931 https://phabricator.wikimedia.org/T223931 for more details. This patch restores pre-2017 behavior.

If you have any questions about the change, or if you notice any irregularities in your data or instrumentation, reach out or tag jlinehan, mpopov, or the Better Use of Data topic on Phabricator.

-Jason