MongoDB .NET/C# Driver

In the context of the MongoDB C# Driver, it is important to distinguish between different networking and pooling concepts:

• Connection: Refers to the driver's internal Connection type. It is an abstraction that manages the lifecycle of a TCP connection to an endpoint. A Connection object is not identical to a TCP connection; it may exist without an active TCP connection at all times.
• Endpoint: Refers to either a mongod or mongos instance.
• Thread: In the context of the C# driver, this refers to a shared-address-space process (a thread).

If you use Guid as your _id and require values to be ascending (to ensure they are inserted at the right-hand side of the index), use the AscendingGuidGenerator.

Important: For the server to correctly recognize the Guids as ascending, you must store them using GuidRepresentation.Standard.

In vanilla medium trust environments, TCP communication is disallowed. To enable the driver to run, you must use a custom medium trust permission system that allows sockets. Copy your existing medium trust policy file and add the following configurations:

1. Add the SocketPermission security class.
2. Add an IPermission for the new SocketPermission class.

<SecurityClass Name="SocketPermission" Description="System.Net.SocketPermission, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"/>

<IPermission class="SocketPermission" version="1" Unrestricted="true"/>

Starting with version 1.7, the default WriteConcern has changed to Acknowledged. To use this new default, you must use the MongoClient class.

If you continue to use the deprecated MongoServer.Create method, the WriteConcern will remain Unacknowledged to maintain backward compatibility with existing code.

// The new way (defaults WriteConcern to Acknowledged)
var connectionString = "mongodb://localhost";
var client = new MongoClient(connectionString);
var server = client.GetServer();
var database = server.GetDatabase("test");

// The old way (deprecated, defaults WriteConcern to Unacknowledged)
var connectionString = "mongodb://localhost";
var server = MongoServer.Create(connectionString); // deprecated
var database = server.GetDatabase("test");

To facilitate automated analysis or comparison, you can export results in the Evergreen format.

Exporting Results

Use the --evergreen option. You can specify a custom output filename using --output or -o. The default filename is evergreen-results.json.

dotnet run -c Release -- --driverBenchmarks --evergreen --output "my-results.json"

All output files (logs, exported JSON, etc.) are stored in a BenchmarkDotNet.Artifacts folder created after execution.

Comparing Runs

Use the Python script located in /scripts/compare-results to compare different benchmark runs. This script requires JSON files generated with the --evergreen option.

To run the driver benchmarks, you must first download the required data and ensure a mongod instance is running on localhost. You can specify a custom connection string using the MONGODB_URI environment variable or the --envVars option.

Prerequisites

1. Download benchmark data: Run /scripts/download-data.sh from the benchmark root directory.
2. Ensure a MongoDB instance is running (default: localhost).

Execution

Run the following command to start the runner with an interactive prompt to select benchmarks:

dotnet run -c Release -- --driverBenchmarks

To specify a custom connection string via command line arguments:

dotnet run -c Release -- --driverBenchmarks --envVars MONGODB_URI:"ConnectionString"

The Save method was updated in version 1.8.3 to ensure correct _id serialization when using custom serializers. Because this new approach is slightly less efficient, you can achieve better performance by calling Insert or Update directly:

• Use Insert if you know the document is new.
• Use Update with an appropriate query and the Upsert flag if you are unsure whether the document exists.