DRIVERS-2884 Avoid connection churn when operations timeout #1675
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ShaneHarvey
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Oct 15, 2024
source/client-side-operations-timeout/tests/connection-churn.yml
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ShaneHarvey
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Apr 17, 2025
| # after maxTimeMS, whereas mongod returns it after | ||
| # max(blockTimeMS, maxTimeMS). Until this ticket is resolved, these tests | ||
| # will not pass on sharded clusters. | ||
| topologies: ["standalone", "replicaset"] |
| - name: findOne | ||
| object: *collection | ||
| arguments: | ||
| timeoutMS: 50 |
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In python this timeout is too small and causes this find to fail before sending anything to the server. The same problem exists in the other tests too. Perhaps all of theses tests should run a setup command (eg ping) to ensure a connection is created and available in the pool, then run the finds. What do you think?
prestonvasquez
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alcaeus,
stIncMale,
baileympearson and
ShaneHarvey
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This PR implements the design for connection pooling improvements described in DRIVERS-2884, based on the CSOT (Client-Side Operation Timeout) spec. It addresses connection churn caused by network timeouts during operations, especially in environments with low client-side timeouts and high latency.
When a connection is checked out after a network timeout, the driver now attempts to resume and complete reading any pending server response (instead of closing and discarding the connection). This may require multiple checkouts.
Each pending response read is subject to a cumulative 3-second static timeout. The timeout is refreshed after each successful read, acknowledging that progress is being made. If no data is read and the timeout is exceeded, the connection is closed.
To reduce unnecessary latency, if the timeout has expired while the connection was idle in the pool, a non-blocking single-byte read is performed; if no data is available, the connection is closed immediately.
This update introduces new CMAP events and logging messages (PendingResponseStarted, PendingResponseSucceeded, PendingResponseFailed) to improve observability of this path.
Please complete the following before merging:
clusters, and serverless).