Smalyshev added a comment.
> I'm not sure I understand why a If-Modified-Since: would not work. How would you see it working? In Varnish, it would be useless since Varnish has no way of knowing if Wikidata item changed since being cached. If we go to the backend, first we are already incurring all the costs of PHP setup, database connection and loading the data just to know whether the data has been edited or not. But there are more complications then that: 1. If-Modified-Since requires a timestamp. Timestamps (in seconds) do not have enough granularity to track changes in Wikidata - there can be many edits within one second. 2. The timestamp we have in the change even is not necessarily the timestamp on the database edit (we could probably ensure it's the same but due to the above it's useless anyway and we have to use revision IDs) 3. In most cases, we can already know if we have certain revision without calling Wikidata - revisions are monotonic, which means if we have revision X in the database and change comes with revision Y with Y<X, there's no point in calling Wikidata with this revision - we already have data better than this change event. Thus, I don't see how and in which scenario using If-Modified-Since would be beneficial. TASK DETAIL https://phabricator.wikimedia.org/T217897 EMAIL PREFERENCES https://phabricator.wikimedia.org/settings/panel/emailpreferences/ To: Smalyshev Cc: Smalyshev, BBlack, Aklapper, Gehel, alaa_wmde, Legado_Shulgin, Nandana, thifranc, AndyTan, Davinaclare77, Qtn1293, Lahi, Gq86, Lucas_Werkmeister_WMDE, GoranSMilovanovic, Th3d3v1ls, Hfbn0, QZanden, EBjune, merbst, LawExplorer, Zppix, _jensen, rosalieper, Jonas, Xmlizer, Wong128hk, jkroll, Wikidata-bugs, Jdouglas, aude, Tobias1984, Manybubbles, faidon, Mbch331, Jay8g, fgiunchedi
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