A story of fixing a memory leak in MiniDumper

MiniDumper is a diagnostic tool for collecting memory dumps of .NET applications. Dumps created by MiniDumper are significantly smaller than full-memory dumps collected by, for example, procdump. However, they contain enough information to diagnose most of the issues in the managed applications. MiniDumper was initially developed by Sasha Goldstein, and I made few contributions to its code base. You may learn more about this tool from Sasha’s or my blog posts.

Recently, one of MiniDumper users reported a memory leak in the application. The numbers looked scary as there was a 20MB leak on each memory dump. The issue stayed opened a few weeks before I finally found a moment to look at it. As it was quite a compelling case, I decided to share with you the diagnostics steps in the hope it proves useful in your investigations.

Minidumper – A Better Way to Create Managed Memory Dumps

This is a repost of my article, originally published on CodeProject on 24 May 2016.

The Story of a Memory Dump

Memory dumps are a common way to diagnose various problems with our applications (such as memory leaks or application hangs). You may think of them as photos which allow you to have a look at the past and notice all the details you might have missed. There are different types of memory dumps which we may compare to different types of photos we take:

• minimal – focus is on one element (such as an exception) and the whole background is blurry, they take very little space on the hardrive (eg. 2MB)
• minidumps with thread and process data/heaps/stacks/exception data, etc. – depending on how many options we choose, they might be very detailed high-resolution pictures or very blurry ones, the range of space they take can vary from tens of MBs to several GBs
• full memory dumps – those can be compared to high-resolution pictures, they are as big as the whole process committed virtual memory

New features coming to minidumper

Some time ago Sasha Goldstein wrote on his blog a post about a new open-source tool he created: minidumper. The idea is great and allows you to create more compact memory dumps for .NET processes. I completely agree with Sasha that most of the time when you are working with .NET processes memory dumps you are focused on .NET memory heap. All native elements are usually not necessary and take a lot of space in dumps. Having said that, I need to admit that there were times when those native parts were invaluable in my diagnosis, such as diagnosing native memory leaks (when using pinvoke) or handle leaks. But those are quite rare and in such situations we have no choice but to use the full memory dumps. For all other .NET problems you are welcome to use minidumper. If you are interested in minidumper internals there is another post on Sasha’s blog which explains them very well.