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CSHARP-5377: Eliminate unnecessary killCursors command when batchSize == limit #1729

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Merged
merged 1 commit into from
Jul 16, 2025
Merged

CSHARP-5377: Eliminate unnecessary killCursors command when batchSize == limit #1729

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148 changes: 148 additions & 0 deletions specifications/crud/tests/unified/find.json
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Original file line number Diff line number Diff line change
Expand Up @@ -151,6 +151,154 @@
]
}
]
},
{
"description": "Find with filter",
"operations": [
{
"object": "collection0",
"name": "find",
"arguments": {
"filter": {
"_id": 1
}
},
"expectResult": [
{
"_id": 1,
"x": 11
}
]
}
]
},
{
"description": "Find with filter, sort, skip, and limit",
"operations": [
{
"object": "collection0",
"name": "find",
"arguments": {
"filter": {
"_id": {
"$gt": 2
}
},
"sort": {
"_id": 1
},
"skip": 2,
"limit": 2
},
"expectResult": [
{
"_id": 5,
"x": 55
},
{
"_id": 6,
"x": 66
}
]
}
]
},
{
"description": "Find with limit, sort, and batchsize",
"operations": [
{
"object": "collection0",
"name": "find",
"arguments": {
"filter": {},
"sort": {
"_id": 1
},
"limit": 4,
"batchSize": 2
},
"expectResult": [
{
"_id": 1,
"x": 11
},
{
"_id": 2,
"x": 22
},
{
"_id": 3,
"x": 33
},
{
"_id": 4,
"x": 44
}
]
}
]
},
{
"description": "Find with batchSize equal to limit",
"operations": [
{
"object": "collection0",
"name": "find",
"arguments": {
"filter": {
"_id": {
"$gt": 1
}
},
"sort": {
"_id": 1
},
"limit": 4,
"batchSize": 4
},
"expectResult": [
{
"_id": 2,
"x": 22
},
{
"_id": 3,
"x": 33
},
{
"_id": 4,
"x": 44
},
{
"_id": 5,
"x": 55
}
]
}
],
"expectEvents": [
{
"client": "client0",
"events": [
{
"commandStartedEvent": {
"command": {
"find": "coll0",
"filter": {
"_id": {
"$gt": 1
}
},
"limit": 4,
"batchSize": 5
},
"commandName": "find",
"databaseName": "find-tests"
}
}
]
}
]
}
]
}
69 changes: 68 additions & 1 deletion specifications/crud/tests/unified/find.yml
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Original file line number Diff line number Diff line change
Expand Up @@ -65,4 +65,71 @@ tests:
batchSize: 2
commandName: getMore
databaseName: *database0Name

-
description: 'Find with filter'
operations:
-
object: *collection0
name: find
arguments:
filter: { _id: 1 }
expectResult:
- { _id: 1, x: 11 }
-
description: 'Find with filter, sort, skip, and limit'
operations:
-
object: *collection0
name: find
arguments:
filter: { _id: { $gt: 2 } }
sort: { _id: 1 }
skip: 2
limit: 2
expectResult:
- { _id: 5, x: 55 }
- { _id: 6, x: 66 }
-
description: 'Find with limit, sort, and batchsize'
operations:
-
object: *collection0
name: find
arguments:
filter: { }
sort: { _id: 1 }
limit: 4
batchSize: 2
expectResult:
- { _id: 1, x: 11 }
- { _id: 2, x: 22 }
- { _id: 3, x: 33 }
- { _id: 4, x: 44 }
-
description: 'Find with batchSize equal to limit'
operations:
-
object: *collection0
name: find
arguments:
filter: { _id: { $gt: 1 } }
sort: { _id: 1 }
limit: 4
batchSize: 4
expectResult:
- { _id: 2, x: 22 }
- { _id: 3, x: 33 }
- { _id: 4, x: 44 }
- { _id: 5, x: 55 }
expectEvents:
- client: *client0
events:
- commandStartedEvent:
command:
find: *collection0Name
filter: { _id: { $gt: 1 } }
limit: 4
# Drivers use limit + 1 for batchSize to ensure the server closes the cursor
batchSize: 5
commandName: find
databaseName: *database0Name
17 changes: 8 additions & 9 deletions src/MongoDB.Driver/Core/Operations/FindOperation.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -46,7 +46,6 @@ internal sealed class FindOperation<TDocument> : IReadOperation<IAsyncCursor<TDo
private BsonValue _comment;
private CursorType _cursorType;
private BsonDocument _filter;
private int? _firstBatchSize;
private BsonValue _hint;
private BsonDocument _let;
private int? _limit;
Expand Down Expand Up @@ -125,12 +124,6 @@ public BsonDocument Filter
set { _filter = value; }
}

public int? FirstBatchSize
{
get { return _firstBatchSize; }
set { _firstBatchSize = Ensure.IsNullOrGreaterThanOrEqualToZero(value, nameof(value)); }
}

public BsonValue Hint
{
get { return _hint; }
Expand Down Expand Up @@ -249,7 +242,13 @@ public BsonDocument CreateCommand(ConnectionDescription connectionDescription, I
var wireVersion = connectionDescription.MaxWireVersion;
FindProjectionChecker.ThrowIfAggregationExpressionIsUsedWhenNotSupported(_projection, wireVersion);

var firstBatchSize = _firstBatchSize ?? (_batchSize > 0 ? _batchSize : null);
var batchSize = _batchSize;
// https://github.com/mongodb/specifications/blob/668992950d975d3163e538849dd20383a214fc37/source/crud/crud.md?plain=1#L803
if (batchSize.HasValue && batchSize == _limit)
{
batchSize = _limit + 1;
}

var isShardRouter = connectionDescription.HelloResult.ServerType == ServerType.ShardRouter;

var effectiveComment = _comment;
Expand All @@ -271,7 +270,7 @@ public BsonDocument CreateCommand(ConnectionDescription connectionDescription, I
{ "hint", effectiveHint, effectiveHint != null },
{ "skip", () => _skip.Value, _skip.HasValue },
{ "limit", () => Math.Abs(_limit.Value), _limit.HasValue && _limit != 0 },
{ "batchSize", () => firstBatchSize.Value, firstBatchSize.HasValue },
{ "batchSize", () => batchSize.Value, batchSize.HasValue && batchSize > 0 },
{ "singleBatch", () => _limit < 0 || _singleBatch.Value, _limit < 0 || _singleBatch.HasValue },
{ "comment", effectiveComment, effectiveComment != null },
{ "maxTimeMS", () => MaxTimeHelper.ToMaxTimeMS(effectiveMaxTime.Value), effectiveMaxTime.HasValue },
Expand Down
53 changes: 0 additions & 53 deletions tests/MongoDB.Driver.Tests/Core/Operations/FindOperationTests.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -136,7 +136,6 @@ public void constructor_should_initialize_instance()
subject.Comment.Should().BeNull();
subject.CursorType.Should().Be(CursorType.NonTailable);
subject.Filter.Should().BeNull();
subject.FirstBatchSize.Should().NotHaveValue();
subject.Hint.Should().BeNull();
subject.Limit.Should().NotHaveValue();
subject.Max.Should().BeNull();
Expand Down Expand Up @@ -352,30 +351,6 @@ public void CreateCommand_should_return_expected_result_when_Filter_is_set(
result.Should().Be(expectedResult);
}

[Theory]
[ParameterAttributeData]
public void CreateCommand_should_return_expected_result_when_FirstBatchSize_is_set(
[Values(null, 0, 1)]
int? firstBatchSize)
{
var subject = new FindOperation<BsonDocument>(_collectionNamespace, BsonDocumentSerializer.Instance, _messageEncoderSettings)
{
FirstBatchSize = firstBatchSize
};

var connectionDescription = OperationTestHelper.CreateConnectionDescription();
var session = OperationTestHelper.CreateSession();

var result = subject.CreateCommand(connectionDescription, session);

var expectedResult = new BsonDocument
{
{ "find", _collectionNamespace.CollectionName },
{ "batchSize", () => firstBatchSize.Value, firstBatchSize.HasValue }
};
result.Should().Be(expectedResult);
}

[Theory]
[ParameterAttributeData]
public void CreateCommand_should_return_expected_result_when_Hint_is_set(
Expand Down Expand Up @@ -937,34 +912,6 @@ public void Filter_get_and_set_should_work(
result.Should().BeSameAs(value);
}

[Theory]
[ParameterAttributeData]
public void FirstBatchSize_get_and_set_should_work(
[Values(null, 0, 1, 2)]
int? value)
{
var subject = new FindOperation<BsonDocument>(_collectionNamespace, BsonDocumentSerializer.Instance, _messageEncoderSettings);

subject.FirstBatchSize = value;
var result = subject.FirstBatchSize;

result.Should().Be(value);
}

[Theory]
[ParameterAttributeData]
public void FirstBatchSize_set_should_throw_when_value_is_invalid(
[Values(-2, -1)]
int value)
{
var subject = new FindOperation<BsonDocument>(_collectionNamespace, BsonDocumentSerializer.Instance, _messageEncoderSettings);

var exception = Record.Exception(() => { subject.FirstBatchSize = value; });

var argumentOutOfRangeException = exception.Should().BeOfType<ArgumentOutOfRangeException>().Subject;
argumentOutOfRangeException.ParamName.Should().Be("value");
}

[Theory]
[ParameterAttributeData]
public void Hint_get_and_set_should_work(
Expand Down