System.OutOfMemoryException while merging not so big files

[xumix]

Describe the bug
System.OutOfMemoryException while merging not so big files, trying to eat 10+ Gb in build pipeline

To Reproduce
dotnet tool install --global dotnet-reportgenerator-globaltool - newest at the moment of writing (5.5.5)

$ reportgenerator "-reports:${CI_PROJECT_DIR}/artifacts/tests/coverage_*.xml" "-targetdir:${CI_PROJECT_DIR}/artifacts/tests/merged" -reporttypes:"Cobertura;HtmlSummary"
2026-04-20T15:32:58: Arguments
2026-04-20T15:32:58:  -reports:/builds/pp/pp3/artifacts/tests/coverage_*.xml
2026-04-20T15:32:58:  -targetdir:/builds/pp/pp3/artifacts/tests/merged
2026-04-20T15:32:58:  -reporttypes:Cobertura;HtmlSummary
2026-04-20T15:33:22: Error during reading report '/builds/pp/pp3/artifacts/tests/coverage_Pp3.Companies.Tests.xml' (Size: 50.7MB): Multiple errors
Exception of type 'System.OutOfMemoryException' was thrown.
Exception of type 'System.OutOfMemoryException' was thrown.
Exception of type 'System.OutOfMemoryException' was thrown.
Exception of type 'System.OutOfMemoryException' was thrown.
Exception of type 'System.OutOfMemoryException' was thrown.
Exception of type 'System.OutOfMemoryException' was thrown.
Exception of type 'System.OutOfMemoryException' was thrown.
Exception of type 'System.OutOfMemoryException' was thrown.
Exception of type 'System.OutOfMemoryException' was thrown.
Exception of type 'System.OutOfMemoryException' was thrown.
2026-04-20T15:33:32: Error during reading report '/builds/pp/pp3/artifacts/tests/coverage_Pp3.Mailer.Tests.xml' (Size: 52MB): Multiple errors
Exception of type 'System.OutOfMemoryException' was thrown.
Exception of type 'System.OutOfMemoryException' was thrown.
Exception of type 'System.OutOfMemoryException' was thrown.
Exception of type 'System.OutOfMemoryException' was thrown.
Exception of type 'System.OutOfMemoryException' was thrown.
2026-04-20T15:33:40: Error during reading report '/builds/pp/pp3/artifacts/tests/coverage_Pp3.Tests.xml' (Size: 61MB): Multiple errors
Exception of type 'System.OutOfMemoryException' was thrown.
Exception of type 'System.OutOfMemoryException' was thrown.
Exception of type 'System.OutOfMemoryException' was thrown.
Exception of type 'System.OutOfMemoryException' was thrown.
Exception of type 'System.OutOfMemoryException' was thrown.
Exception of type 'System.OutOfMemoryException' was thrown.
Exception of type 'System.OutOfMemoryException' was thrown.
Exception of type 'System.OutOfMemoryException' was thrown.

The files in charge: https://drive.google.com/drive/folders/1cz6Ff9E3aZTIrVffQxyeFCnyoZ5HwXnS?usp=drive_link

[danielpalme]

Thanks for the sample files.

The problem is not the size of the coverage files.

The root cause is the following:
Over 12.000 classes are defined in a single file (EisTypes.cs). This file is really long (145.229 lines).

When ReportGenerator iterates over the classes, it generates arrays with coverage information for each file a class is defined in.
12.000 times 145.229 consumes a lot of memory.

To work around the issue you could:

• Split the large file into a separate file for each class (I assume that the classes within this file are generated.)
• Exclude this file from the coverage report -filefilters:-*EisTypes.cs

[xumix]

@danielpalme Unfortunately I'll not be able to split the file, will try to exclude it. Thanks!
But anyway, the memory usage seems excessive even for 12k types file.

[danielpalme]

I was able to reduce the memory usage significantly for large files.
You could try the new release 5.5.7 without the filefilters.

[xumix]

I was able to reduce the memory usage significantly for large files. You could try the new release 5.5.7 without the filefilters.

Thank you!