Mark server unknown and clear the pool when background connections fail.
Eagerly evict threads from the wait queue when pool is paused. Evicted
threads will raise the following error:
AutoReconnect('localhost:27017: connection pool paused')
Introduce PoolClearedEvent and ConnectionPoolListener.pool_ready.
CMAP spec test changes:
- CMAP unit tests should not use real monitors
- Assert that CMAP threads complete all scheduled operations
Change the driver to maintain a count of in-progress operations to each
server (per client). When selecting a mongos server, the driver now picks
2 suitable servers at random and selects the server with fewer in-progress
operations. Previously, the driver selected a mongos server at random.
The new behavior is intended to route operations away from unhealthy or
slow servers in highly concurrent single client workloads.
PYTHON-2460 Only reset Pool.active_sockets to 0 after a fork()
MongoClient now requires 2 connections and 2 threads to each MongoDB 4.4+ server.
With one connection, the server streams (or pushes) updated heartbeat info.
With the other connection, the client periodically pings the server to
establish an accurate round-trip time (RTT). This change optimizes the
discovery of server state changes such as replica set elections.
Additional changes:
- Mark server Unknown before retrying isMaster check.
- Always reset the pool _after_ marking the server unknown.
- Configure fail point before creating the client in test SpecRunner.
- Unfreeze with replSetFreeze:0 to ensure a speedy elections in test suite.
