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ConcurrentDictionary Count is slow #100853

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fredwangwang opened this issue Apr 10, 2024 · 3 comments
Closed

ConcurrentDictionary Count is slow #100853

fredwangwang opened this issue Apr 10, 2024 · 3 comments
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area-System.Collections tenet-performance Performance related issue

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@fredwangwang
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Description

During one of the performance testing, found out that calling to ConcurrentDictionary.Count is contributing significant time to a hot path.

Configuration

win x64 .net8.0

Regression?

Dont think this is a regression.

Analysis

Looking into the implementation for Count, found out that each time Count is called, it is locking the entire dictionary and iterate through all buckets to get a sum.

It seems that the performance would be much better to keep an atomic counter so that get Count is instant.

https://source.dot.net/#System.Collections.Concurrent/System/Collections/Concurrent/ConcurrentDictionary.cs,1116

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@fredwangwang fredwangwang added the tenet-performance Performance related issue label Apr 10, 2024
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Tagging subscribers to this area: @dotnet/area-system-collections
See info in area-owners.md if you want to be subscribed.

@dotnet-policy-service dotnet-policy-service bot added the untriaged New issue has not been triaged by the area owner label Apr 10, 2024
@EgorBo
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EgorBo commented Apr 10, 2024

See #15249 (comment)

@eiriktsarpalis
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Duplicate of #15249

@eiriktsarpalis eiriktsarpalis marked this as a duplicate of #15249 Apr 10, 2024
@dotnet-policy-service dotnet-policy-service bot removed the untriaged New issue has not been triaged by the area owner label Apr 10, 2024
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@EgorBo @eiriktsarpalis @fredwangwang