As a user of the WDQS UI I want to know the lag of the servers so that I can more easily evaluate if the results I see are stale.
The way it is designed today is to use a dedicated triple in the store:
<http://www.wikidata.org> schema:dateModified "2021-03-12T20:59:57Z"^^xsd:dateTime
This triple being an artifact of the update it was decided to not maintain it with the new updater. Reason was that the triple seemed the wrong choice for storing metrics regarding the health of the system.
On the other hand the WDQS UI is currently reporting the lag metric using this triple despite being inaccurate (there are no guarantee that the lag reported is from the same server than the one that will serve the results displayed).
Short term solution is perhaps to still maintain this triple from the new updater and figure out better long term solution to properly inform users of the latency of the results they see.
- the triple <http://www.wikidata.org> schema:dateModified TIMESTAMP is maintained by the new updater
- create a ticket describing a better long term solution