In SPM-4003, new logic was added to ConnectionPool to not enter failed mode when receiving establishment failures that may be indicative of connection rate limiting on the remote host. Originally, this logic would also cause the pool to enter a throttling state, which would reduce the number of connections it created temporarily. Upon further analysis, this led to certain undesirable behaviors in the pool and was thus reverted in SERVER-119690.

However, without throttling of any kind, a pool will immediately start spawning new connections after being rate limited, which reduces the effectiveness of the rate limiter and can waste resource both on client and server. We should revisit introducing some amount of throttling in a way that addresses the concerns that were discovered when investigating SERVER-119690.