For warm/active DC case, we want to avoid cross-DC queries when the master is in another data center. We should cut down on master queries for this reason. Also, doing master queries on read makes the master a SPOF on read requests (not just write requests).
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IIRC the biggest danger here is getting stale pages (from slave) rendered and stuck in the parsercache or varnish cache layer. More careful cache purging after save combined with a cleaner post-save display that doesn't rely on the save having propagated before a redirect might help with this.
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Change 351790 had a related patch set uploaded (by Aaron Schulz; owner: Aaron Schulz):
[mediawiki/extensions/CentralAuth@master] Add $flags parameter to renameInProgressOn()