SERVER-12861 Introduce a maxStalenessMS option when querying secondaries

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• Closed

SERVER-3346 MAX SLAVE LAG - Features to provide a more stable Replication Set under high load

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• Closed

SERVER-25842 Secondary started accepting queries before syncing(replSet still syncing, not yet to minValid optime)

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• Closed

SERVER-23892 Do periodic replicated writes every 10 seconds while idle (for maxStalenessMS)

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• Closed

SERVER-4935 Mark node Recovering when replication lag exceeds a configured threshold

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• Closed