# Nested loops are consuming a lot of memory

**URL:** <https://discourse.julialang.org/t/nested-loops-are-consuming-a-lot-of-memory/6010>\
**Category:** General Usage\
**Tags:** memory, memory-allocation\
**Created:** [September 20, 2017, 8:38pm UTC](https://discourse.julialang.org/t/nested-loops-are-consuming-a-lot-of-memory/6010 "2017-09-20T20:38:19Z")\
**Posts on this page:** 7\
**Page:** 1

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**Author:** ![tryingtosolve](https://avatars.discourse-cdn.com/v4/letter/t/bbe5ce/32.png) [@tryingtosolve](https://discourse.julialang.org/u/tryingtosolve)\
**Post date:** [September 20, 2017, 8:38pm UTC](https://discourse.julialang.org/t/nested-loops-are-consuming-a-lot-of-memory/6010/1 "2017-09-20T20:38:19Z")

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I have a nested loop iteration scheme that’s taking up a lot of memory. I do understand that I should not have globals but even after I included everything in a function, the memory situation didn’t improve. It just accumulates after each iteration as if there is no garbage collection.

Here is a workable example that’s similar to my code.

I have two files. First, **functions.jl** :

```julia
##functions.jl
module functions

function getMatrix(A)
    L = rand(A,A);
    return L;
end

function loopOne(A, B)
    res = 0;
    for i = 1:B
        res = inv(getMatrix(A));
    end
    return(res);
end

end

```

Second file **main.j** l:

```julia
##main.jl
include("functions.jl")
function main(C)
    A = 50;
    B = 30;
    res = 0;
    for i =1:C
        mat = functions.loopOne(A,B);
        res = mat .+ 1;
    end
    return res;
end
main(100)

```

When I execute ` julia main.jl`, the memory increases as I extend the loop in `main(C)` (sometimes to more than millions of allocations and 10GiBs if I increase `C` to 10,000).

**Issue** : I want to reduce the memory consumption. Since I’m not creating any new arrays throughout the loop, the consumption of memory should be pretty much close to constant regardless of how much I increase `C`. However, that’s not the case here. The variables that I have are just `L, A, B, res, mat`. My code just updates them throughout. I don’t understand why it’s creating new arrays.

**What I want** : I’m assigning new values to variables with the same names, as the previously assigned values are useless when the loop enters into a new iteration. Therefore, I want the memory usage to stay constant.

I know that the example looks useless but it resembles the structure that I have. Can someone please help? Thank you.

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**Author:** ![tkoolen](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/tkoolen/32/1603_2.png) [@tkoolen](https://discourse.julialang.org/u/tkoolen)\
**Post date:** [September 20, 2017, 8:47pm UTC](https://discourse.julialang.org/t/nested-loops-are-consuming-a-lot-of-memory/6010/2 "2017-09-20T20:47:23Z")

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Could you update your example so that it actually runs? Right now, `functions.getMatrix` and `functions.loopOne` are undefined, and the `res` that you’re trying to return in `loopOne` isn’t in scope.

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**Author:** ![favba](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/favba/32/2735_2.png) [@favba](https://discourse.julialang.org/u/favba)\
**Post date:** [September 20, 2017, 8:51pm UTC](https://discourse.julialang.org/t/nested-loops-are-consuming-a-lot-of-memory/6010/3 "2017-09-20T20:51:03Z")

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I’d suggest posting your actual code. That way people could see which new array allocation is needed or not.  
But I don’t know if get your problem right. Are you worried about unnecessary allocation or garbage collection not being triggered?

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**Author:** ![tryingtosolve](https://avatars.discourse-cdn.com/v4/letter/t/bbe5ce/32.png) [@tryingtosolve](https://discourse.julialang.org/u/tryingtosolve)\
**Post date:** [September 20, 2017, 10:53pm UTC](https://discourse.julialang.org/t/nested-loops-are-consuming-a-lot-of-memory/6010/4 "2017-09-20T22:53:10Z")

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@favba @tkoolen

I updated the code so this should work. The issue is that as I increase `C` in `main(C)`, the memory consumption increases. How can I prevent this from happening? I’m not creating any new arrays throughout the loop so intuitively this shouldn’t happen. I don’t have any globals either.

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**Author:** ![fredrikekre](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/fredrikekre/32/1688_2.png) [@fredrikekre](https://discourse.julialang.org/u/fredrikekre)\
**Post date:** [September 20, 2017, 10:57pm UTC](https://discourse.julialang.org/t/nested-loops-are-consuming-a-lot-of-memory/6010/5 "2017-09-20T22:57:38Z")

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I’m confused; you create a lot of new arrays so naturally the number of allocations become larger with each loop? Also, what version are you on? Your example still does not run on 0.6.

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**Author:** ![tryingtosolve](https://avatars.discourse-cdn.com/v4/letter/t/bbe5ce/32.png) [@tryingtosolve](https://discourse.julialang.org/u/tryingtosolve)\
**Post date:** [September 20, 2017, 11:01pm UTC](https://discourse.julialang.org/t/nested-loops-are-consuming-a-lot-of-memory/6010/6 "2017-09-20T23:01:32Z")

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@fredrikekre

Fixed the code again. This time it should work.

I’m using 0.6. Why are there new arrays? The variables that I have are just `L, A, B, res, mat `? My code just updates them throughout.

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**Author:** ![mbauman](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mbauman/32/31082_2.png) [@mbauman](https://discourse.julialang.org/u/mbauman)\
**Post date:** [September 20, 2017, 11:03pm UTC](https://discourse.julialang.org/t/nested-loops-are-consuming-a-lot-of-memory/6010/7 "2017-09-20T23:03:10Z")

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You’ve also posted this over at StackOverflow, where it has attracted a nice answer. Please don’t simultaneously post the same question in multiple places — it splits the discussion and duplicates the efforts of many helpful volunteers.

> <https://stackoverflow.com/questions/46330121/julia-nested-loops-are-consuming-a-lot-of-memory>