Fixes a noisy OperationFailure: Authentication failed error.
Do not attempt to create unneeded connections to arbiters, ghosts,
hidden members, or unknown members.
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
At most 2 connections can be in the pending state per connection pool.
The pending state covers all the work required to setup a new connection
including TCP, TLS, and MongoDB authentication. For example, if two
threads are currently creating connections, a third thread will wait for
either an existing connection to be checked back into the pool or for
one of the two threads to finish creating a connection.
The change reduces the likelihood of connection storms and improves the
driver's ability to reuse existing connections.
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.
