# How to debug a non-deterministic StackOverflowError?

**URL:** <https://discourse.julialang.org/t/how-to-debug-a-non-deterministic-stackoverflowerror/24718>\
**Category:** General Usage\
**Created:** [May 29, 2019, 8:19am UTC](https://discourse.julialang.org/t/how-to-debug-a-non-deterministic-stackoverflowerror/24718 "2019-05-29T08:19:20Z")\
**Posts on this page:** 1\
**Showing post:** 9

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**Author:** ![Tamas\_Papp](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/tamas_papp/32/25949_2.png) [@Tamas\_Papp](https://discourse.julialang.org/u/Tamas_Papp)\
**Post date:** [May 29, 2019, 11:08am UTC](https://discourse.julialang.org/t/how-to-debug-a-non-deterministic-stackoverflowerror/24718/9 "2019-05-29T11:08:56Z")

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> [@jules](#):
>
> how can the error appear only sometimes if I have exactly the same testset every time? Many times it runs fine

> [@Understanding Dict](https://discourse.julialang.org/t/understanding-dict/5602/):
>
> Hi everyone. I am coming from python background. In python, dictionary keys cannot be mutable because it is based on hash table. However, keys in Dict in julia do not need to be immutable. I wonder how this is achieved?

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