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Type:
Improvement
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Resolution: Duplicate
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Priority:
Unknown
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None
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Affects Version/s: None
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Component/s: None
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None
We encountered significant memory allocation and GC pressure while using the mongo-csharp-driver (v2.25.0). BSON binary serialization in the driver has become a memory allocation hotspot on our server. Below are the memory allocation metrics captured via dotTrace over 5 minutes:
| Type/Class | Memory Allocation | Percentage |
| MongoDB.Bson.IO.BsonBinaryWriterContext | 29,909 MB | 10.6% |
| Systernint32 | 20,838 MB | 7.4% |
| Aki.Define.EntityDbData | 15,622 MB | 5.5% |
| System.String | 11,642 MB | 4.1% |
| Enumerator[MongoDB.Bson.Serialization.BsonMemberMap] | 10,250 MB | 3.6% |
| System.Byte[] | 9,650 MB | 3.4% |
| Systernint32n | 8,805 MB | 3.1% |
| System.Boolean | 6,816 MB | 2.4% |
| Entry[System.String,Serilog.Events.LogEventPropertyValue[] | 5,561 MB | 2.0% |
| System.Char[] | 5,306 MB | 1.9% |
BsonBinaryWriterContext
BsonBinaryWriter.WriteStartDocument
https://github.com/mongodb/mongo-csharp-driver/blob/46eafc9d64a7f2147b49046f51e7fdd28c7e391f/src/MongoDB.Bson/IO/BsonBinaryWriter.cs#L638
BsonBinaryWriter.WriteStartArray
https://github.com/mongodb/mongo-csharp-driver/blob/46eafc9d64a7f2147b49046f51e7fdd28c7e391f/src/MongoDB.Bson/IO/BsonBinaryWriter.cs#L614
System.Int32
boxing allocations
https://github.com/mongodb/mongo-csharp-driver/blob/46eafc9d64a7f2147b49046f51e7fdd28c7e391f/src/MongoDB.Bson/Serialization/Serializers/BsonClassMapSerializer.cs#L629
Enumerator
Iterator boxing
https://github.com/mongodb/mongo-csharp-driver/blob/46eafc9d64a7f2147b49046f51e7fdd28c7e391f/src/MongoDB.Bson/Serialization/Serializers/BsonClassMapSerializer.cs#L573
https://github.com/mongodb/mongo-csharp-driver/blob/46eafc9d64a7f2147b49046f51e7fdd28c7e391f/src/MongoDB.Bson/Serialization/Serializers/BsonClassMapSerializer.cs#L339
System.Byte[]
86% of the System.Byte[] allocations are generated by the MongoDB C# driver
https://github.com/mongodb/mongo-csharp-driver/blob/46eafc9d64a7f2147b49046f51e7fdd28c7e391f/src/MongoDB.Bson/IO/ArrayElementNameAccelerator.cs#L71
System.Boolean
System.Boolean
Boxing allocations.
Same root cause as System.Int32.
Does the driver development team have an optimisation plan for memory allocation? 
- duplicates
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CSHARP-5575 Serialization performance improvements
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- Backlog
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