DRIVERS-3218 Avoid clearing the connection pool when the server connection rate limiter triggers #1855

blink1073 · 2025-11-11T15:44:50Z

Replaces #1852

Please complete the following before merging:

Is the relevant DRIVERS ticket in the PR title?

Update changelog.
Test changes in at least one language driver. PYTHON-5517 Simplify pool backpressure behavior mongo-python-driver#2611
Test these changes against all server versions and topologies (including standalone, replica set, and sharded
clusters).

…ction rate limiter triggers

blink1073 · 2025-11-11T15:48:06Z

source/connection-monitoring-and-pooling/tests/cmap-format/pool-create-min-size-error.yml

  data:
    failCommands: ["isMaster","hello"]
-    closeConnection: true
+    blockConnection: true


While we are discouraged from changing existing tests, these test still pass without the backpressure changes, and this avoids adding a new runOnRequirement.

https://spruce.mongodb.com/version/6914e629b2e3e30007b7c384/tasks?sorts=STATUS%3AASC%3BBASE_STATUS%3ADESC

source/connection-monitoring-and-pooling/connection-monitoring-and-pooling.md

source/server-discovery-and-monitoring/server-discovery-and-monitoring.md

source/server-discovery-and-monitoring/tests/unified/backpressure-network-error-fail.yml

baileympearson

Discussed some test issues with Steve on slack, here's some other comments I had. My POC in Node is passing locally with the changes Steve is planning to make; once I have updated tests I'll test my POC in CI and hopefully everything passes.

source/server-discovery-and-monitoring/server-discovery-and-monitoring.md

source/server-discovery-and-monitoring/tests/unified/backpressure-network-error-fail.yml

source/server-discovery-and-monitoring/server-discovery-and-monitoring-tests.md

source/server-discovery-and-monitoring/server-discovery-and-monitoring.md

source/server-discovery-and-monitoring/server-discovery-and-monitoring-tests.md

…nitoring.md Co-authored-by: Bailey Pearson <bailey.pearson@gmail.com>

blink1073 · 2025-11-20T15:37:01Z

Note: I haven't yet updated the prose test implementation in pymongo. I'm working on that next.

baileympearson

One minor comment.

Second implementation in Node is passing: https://spruce.mongodb.com/version/691f7e221be6180007ecf081/tasks?sorts=STATUS%3AASC%3BBASE_STATUS%3ADESC

source/connection-monitoring-and-pooling/connection-monitoring-and-pooling.md

baileympearson · 2025-11-21T17:00:31Z

source/connection-monitoring-and-pooling/connection-monitoring-and-pooling.md


 ## Changelog

+- 2025-XX-YY: Add handling of backpressure error labels.


changelog dates?

blink1073 · 2025-11-21T18:15:18Z

source/server-discovery-and-monitoring/server-monitoring.md

 many clients start at once. A client's subsequent scans of the mongoses are always in the same order, since their
 lastUpdateTimes are always in the same order by the time a scan ends.

+##### Handling of backpressure labels


@kevinAlbs We added this section specifically for the C Driver. Does this make sense?

kevinAlbs · 2025-11-25T13:20:22Z

source/server-discovery-and-monitoring/server-monitoring.md

+                  # Note: for single-threaded monitors, only clear if the `SystemOverloadedError` is not applied to the
+                  # error.


Suggest removing this Note:. This is in the "Monitor thread" section. The C driver single-threaded client does not implement the "Streaming Protocol" (only polling). I think the new "Handling of backpressure labels" is enough.

Great, thank you!

I've pinged you for one more approval for this change

…RS-3218-2

kevinAlbs

Additions to server-monitoring.md LGTM with a typo fix.

source/server-discovery-and-monitoring/server-monitoring.md

Co-authored-by: Kevin Albertson <kevin.eric.albertson@gmail.com>

DRIVERS-3218 Avoid clearing the connection pool when the server conne…

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…ction rate limiter triggers

blink1073 requested review from a team as code owners November 11, 2025 15:44

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blink1073 mentioned this pull request Nov 11, 2025

DRIVERS-3218 Avoid clearing the connection pool when the server connection rate limiter triggers #1852

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Co-authored-by: Kevin Albertson <kevin.eric.albertson@gmail.com>


		## Changelog

		- 2025-XX-YY: Add handling of backpressure error labels.

		# Note: for single-threaded monitors, only clear if the `SystemOverloadedError` is not applied to the
		# error.

DRIVERS-3218 Avoid clearing the connection pool when the server connection rate limiter triggers #1855

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DRIVERS-3218 Avoid clearing the connection pool when the server connection rate limiter triggers #1855

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