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PYTHON-4780 Implement fast path for server selection with Primary #2416

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Merged
merged 11 commits into from
Jul 22, 2025
Merged

PYTHON-4780 Implement fast path for server selection with Primary #2416

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PYTHON-4780 Implement fast path for server selection with Primary
blink1073 Jul 2, 2025
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PYTHON-4780 Implement fast path for server selection with Primary
blink1073 Jul 3, 2025
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fix zizmor
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fix zizmor
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746e8d5
update test
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Merge branch 'master' of github.com:mongodb/mongo-python-driver into …
blink1073 Jul 3, 2025
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update readme
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address review
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13 changes: 1 addition & 12 deletions .github/workflows/zizmor.yml
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Expand Up @@ -17,16 +17,5 @@ jobs:
uses: actions/checkout@v4
with:
persist-credentials: false
- name: Setup Rust
uses: actions-rust-lang/setup-rust-toolchain@fb51252c7ba57d633bc668f941da052e410add48 # v1
- name: Get zizmor
run: cargo install zizmor
- name: Run zizmor 🌈
run: zizmor --format sarif . > results.sarif
env:
GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
- name: Upload SARIF file
uses: github/codeql-action/upload-sarif@39edc492dbe16b1465b0cafca41432d857bdb31a # v3
with:
sarif_file: results.sarif
category: zizmor
uses: zizmorcore/zizmor-action@1c7106082dbc1753372e3924b7da1b9417011a21
2 changes: 1 addition & 1 deletion README.md
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Expand Up @@ -14,7 +14,7 @@ a native Python driver for MongoDB, offering both synchronous and asynchronous A
[gridfs](https://github.com/mongodb/specifications/blob/master/source/gridfs/gridfs-spec.md/)
implementation on top of `pymongo`.

PyMongo supports MongoDB 4.0, 4.2, 4.4, 5.0, 6.0, 7.0, and 8.0. PyMongo follows [semantic versioning](https://semver.org/spec/v2.0.0.html) for its releases.
PyMongo supports MongoDB 4.0, 4.2, 4.4, 5.0, 6.0, 7.0, and 8.0. PyMongo follows [semantic versioning](https://semver.org/spec/v2.0.0.html) for its releases.

## Support / Feedback

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10 changes: 9 additions & 1 deletion pymongo/topology_description.py
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Expand Up @@ -34,7 +34,7 @@
from bson.objectid import ObjectId
from pymongo import common
from pymongo.errors import ConfigurationError, PyMongoError
from pymongo.read_preferences import ReadPreference, _AggWritePref, _ServerMode
from pymongo.read_preferences import Primary, ReadPreference, _AggWritePref, _ServerMode
from pymongo.server_description import ServerDescription
from pymongo.server_selectors import Selection
from pymongo.server_type import SERVER_TYPE
Expand Down Expand Up @@ -324,6 +324,14 @@ def apply_selector(
description = self.server_descriptions().get(address)
return [description] if description else []

# Primary selection fast path.
if self.topology_type == TOPOLOGY_TYPE.ReplicaSetWithPrimary and isinstance(
selector, Primary
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My one concern is that technically this could be a breaking change if a user is subclassing Primary and overriding __call__ to do something special during server selection. One simple way to avoid that risk is doing type(selector) is Primary rather than isinstance. Or we could document the potential breaking change.

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I went with the code modification option

):
for sd in self._server_descriptions.values():
if sd.server_type == SERVER_TYPE.RSPrimary:
return [sd]
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Oh one more thing, don't we have to call the custom_selector here if one was provided?

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And add a test for it?

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I'll have to defer for now, working on a HELP ticket

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Done


selection = Selection.from_topology_description(self)
# Ignore read preference for sharded clusters.
if self.topology_type != TOPOLOGY_TYPE.Sharded:
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4 changes: 2 additions & 2 deletions test/asynchronous/test_server_selection.py
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Expand Up @@ -130,12 +130,12 @@ async def test_selector_called(self):
test_collection = mongo_client.testdb.test_collection
self.addAsyncCleanup(mongo_client.drop_database, "testdb")

# Do N operations and test selector is called at least N times.
# Do N operations and test selector is called at least N-1 times due to fast path.
await test_collection.insert_one({"age": 20, "name": "John"})
await test_collection.insert_one({"age": 31, "name": "Jane"})
await test_collection.update_one({"name": "Jane"}, {"$set": {"age": 21}})
await test_collection.find_one({"name": "Roe"})
self.assertGreaterEqual(selector.call_count, 4)
self.assertGreaterEqual(selector.call_count, 3)

@async_client_context.require_replica_set
async def test_latency_threshold_application(self):
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4 changes: 2 additions & 2 deletions test/test_server_selection.py
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Original file line number Diff line number Diff line change
Expand Up @@ -130,12 +130,12 @@ def test_selector_called(self):
test_collection = mongo_client.testdb.test_collection
self.addCleanup(mongo_client.drop_database, "testdb")

# Do N operations and test selector is called at least N times.
# Do N operations and test selector is called at least N-1 times due to fast path.
test_collection.insert_one({"age": 20, "name": "John"})
test_collection.insert_one({"age": 31, "name": "Jane"})
test_collection.update_one({"name": "Jane"}, {"$set": {"age": 21}})
test_collection.find_one({"name": "Roe"})
self.assertGreaterEqual(selector.call_count, 4)
self.assertGreaterEqual(selector.call_count, 3)

@client_context.require_replica_set
def test_latency_threshold_application(self):
Expand Down
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