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The cache generation is used to decide whether user documents obtained during two separate calls are still "fresh". The generation is incremented whenever an "invalidating" event occurs, such as a user update, or a role deletion, etc. However, we're currently incrementing on user acquisition, which doesn't affect persisted state. This is probably harming our cache use, and causing mongos to frequently re-acquire user data.

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xgen-internal-githook commented on Mon, 30 Dec 2019 19:49:35 +0000: Author: {'name': 'Spencer Jackson', 'email': 'spencer.jackson@mongodb.com', 'username': 'spencerjackson'} Message: SERVER-44922 Prevent User acquisition from incrementing cache generation (cherry picked from commit 47a605826a64d55ff23427deab6f29c5999d1103) Branch: v4.2 https://github.com/mongodb/mongo/commit/b3622d185c1441622602f2a609932b42f8fecd3d xgen-internal-githook commented on Fri, 27 Dec 2019 19:57:22 +0000: Author: {'name': 'Spencer Jackson', 'email': 'spencer.jackson@mongodb.com', 'username': 'spencerjackson'} Message: SERVER-44922 Prevent User acquisition from incrementing cache generation Branch: master https://github.com/mongodb/mongo/commit/47a605826a64d55ff23427deab6f29c5999d1103 kaloian.manassiev commented on Tue, 3 Dec 2019 17:20:33 +0000: Ah ok, thanks. I don't think this is something users do unless for some kind of recovery, so I am not concerned about performance. Thanks for clarifying. spencer.jackson@10gen.com commented on Tue, 3 Dec 2019 16:24:14 +0000: Manually authenticating on a config server. kaloian.manassiev commented on Tue, 3 Dec 2019 15:50:50 +0000: The way I read the description sounds as if MongoS would constantly be refreshing, but I don't think this is the case, right? What user-visible actions would cause the generation to be bumped?

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