I'm working on a JS progam using MongoDB. Our integration tests use the npm library `mongo-memory-server` to download/run a mongod server with ephemeral_for_tests engine.

Each test cleans its test collections by issuing `collection.deleteMany({})` on every modified collection during the test. All these deleteMany are executed in parallel.

When executing many tests, it happens that the mongod server crashes with a segfault.

Workarounds

• If I switch the deletions to be executed 1 by 1 (no parallelism), the crash doesn't occur anymore.
• The crash occurs with mongod 5.0.14 and 6.0.4. If I downgrade to 4.4.18, the crash doesn't occur anymore. 

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I was able to generate 2 core dumps (in attachment) with mongod 6.0.4:

• One sees the segfault in ephemeral_for_test::RadixStore<...>::merge3
• The other in  mongo::ephemeral_for_test::CursorBase::setEndPosition