Marten Memory Issues

I was talking to a colleague this week and he was sharing a story about some memory issues they had with Marten, the DocumentDB and EventStore on top of PostgreSQL.

As I was partially involved during the investigation of the memory issue, I was eager to learn what the root cause was and how they fixed it. Let me share their findings…

Marten extensively uses runtime code generation through Roslyn. Although this is really powerful it comes with a cost in terms of memory usage and cold start issues.

Luckily this is something you can fix by generating the necessary types upfront and include the generated code in your application assemblies.

The documentation describes the required steps quite well:

1. Use the Marten command line extensions for your application
2. Register all document types, compiled query types, and event store projections upfront in your DocumentStore configuration
3. In your deployment process, you'll need to generate the Marten code with dotnet run -- codegen write before actually compiling the build products that will be deployed to production

This will build all the dynamic code and write it to the /Internal/Generated/ folder of your project. The code will be in just two files, Events.cs for the event store support and DocumentStorage.cs.

Now when you compile your application, the newly generated code will be embedded into your application’s entry assembly.

And gone are the memory and cold start issues…

More information:

• https://jeremydmiller.com/2022/03/30/improving-the-development-and-production-time-experience-with-marten-v5/
• https://martendb.io/configuration/prebuilding.html#generating-all-types-upfront