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This article describes performance insights for ConcurrentDictionary<TKey,TValue>.ToArray.
Cause
System.Collections.Concurrent.ConcurrentDictionary.ToArray is resulting in a slow lookup.
Performance insight description
Some ConcurrentDictionary methods, such as ConcurrentDictionary.ToArray, are not concurrent and actually lock the entire collection.
If you need to use lots of ConcurrentDictionary.ToArray method calls, for example, one per request, do not use the default constructor, and instead use a constructor that allows you to specify the concurrency value. The default constructor uses concurrency level equal to the number of cores on the box. Use a smaller number as the concurrency level instead, and then check the overall memory usage.
If you don't need to consider thread-safety, ConcurrentDictionary can be more costly than Dictionary. So check whether you need to use ConcurrentDictionary.
How to investigate a warning
In the CPU Usage tool, click View source code to go to the call tree and source line highlighting view, which shows where the most amount of time is spent in ConcurrentDictionary.ToArray. From this point, trace back to where the method is used and check whether you can check whether you can use another method instead.