Hello all, As you may have noticed, the database replicas sometimes return weird and incorrect results. The cause seems to be that certain queries, under certain circumstances, get different results on labs and production. Because it's the /queries/ that get replicated (and not the underlying data), this causes the replicated databases to drift from the production databases. The issue seems to be mostly related to deletion/undeletion, where revisions get moved to and from the archive table. For more details, please see https://wikitech.wikimedia.org/wiki/Help:Tool_Labs/Database/Replica_drift.
The current (short-time) workaround is regular re-imports of data into the replicas. To do so effectively, it helps to have an overview of queries that do not yield the expected result. If you encounter an odd result, please report it in a comment at https://phabricator.wikimedia.org/T138967. The more long-term solution lies in new database servers with a different server configuration (and in changes to how MediaWiki runs queries). The new database servers have been ordered, but installation and configuration will take some time. We hope to have them set up somewhere in the coming months. Best, Merlijn
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