This article uses benchmarkdotnet To test the performance of a dictionary, two different ways of writing can be used when using a dictionary to obtain a possible value, so this paper analyses the performance of the two ways of writing.

The following two different methods can be used to determine the existence of a value and obtain it if it exists

One way is to use TryGetValue. See the following code

            if (Dictionary.TryGetValue(xx, out var foo))
            {
            }

Another way is to determine if there is one and then retrieve it. See the following code

if(Dictionary.ContainsKey(xx))
{
	var foo = Dictionary[xx];
}

So this article uses benchmarkdotnet Testing the performance of two methods

The following is the data for testing, and the code for testing is at the end of this article. The TryGetExist method here is to try to get a value that exists. ContainGetExist, on the other hand, first determines whether a value exists, and if it exists, attempts to obtain it.

BenchmarkDotNet=v0.10.14, OS=Windows 10.0.17134
Intel Core i7-6700 CPU 3.40GHz (Skylake), 1 CPU, 8 logical and 4 physical cores
Frequency=3328130 Hz, Resolution=300.4690 ns, Timer=TSC
  [Host]     : .NET Framework 4.7 (CLR 4.0.30319.42000), 64bit RyuJIT-v4.7.3132.0  [AttachedDebugger]
  DefaultJob : .NET Framework 4.7 (CLR 4.0.30319.42000), 64bit RyuJIT-v4.7.3132.0

Method	Mean	Error	StdDev	Median
TryGetExist	30.26 ns	0.6057 ns	0.5949 ns	30.11 ns
ContainGetExist	46.36 ns	1.0883 ns	3.1919 ns	44.90 ns
TryGetNoExist	20.23 ns	0.4661 ns	0.7658 ns	19.93 ns
ContainGetNoExist	18.68 ns	0.2569 ns	0.2403 ns	18.66 ns

Comparing the performance of Concurrent Dictionary thread-safe classes, that is, replacing the dictionary of the Foo test class above with that of Concurrent Dictionary without any modification. Here is the test data. You can see that the performance of using TryGetValue is still better.

BenchmarkDotNet=v0.10.14, OS=Windows 10.0.17134
Intel Core i7-6700 CPU 3.40GHz (Skylake), 1 CPU, 8 logical and 4 physical cores
Frequency=3328130 Hz, Resolution=300.4690 ns, Timer=TSC
  [Host]     : .NET Framework 4.7 (CLR 4.0.30319.42000), 64bit RyuJIT-v4.7.3132.0  [AttachedDebugger]
  DefaultJob : .NET Framework 4.7 (CLR 4.0.30319.42000), 64bit RyuJIT-v4.7.3132.0

Method	Mean	Error	StdDev	Median
TryGetExist	31.20 ns	0.4644 ns	0.3625 ns	31.17 ns
ContainGetExist	66.80 ns	2.4692 ns	7.2806 ns	63.84 ns
TryGetNoExist	20.07 ns	0.1254 ns	0.1112 ns	20.04 ns
ContainGetNoExist	27.63 ns	0.4230 ns	0.3956 ns	27.65 ns

All code

    public class Foo
    {
        /// <inheritdoc />
        public Foo()
        {
            var ran = new Random();
            bool set = false;
            for (int i = 0; i < 100000; i++)
            {
                LazyDictionary[ran.Next().ToString() + "-" + i.ToString()] = ran.Next().ToString();
                if (!set)
                {
                    if (ran.Next() < i)
                    {
                        set = true;
                        LazyDictionary["lindexi"] = "Teasing ratio";
                    }
                }
            }
        }

        [Benchmark]
        public void TryGetExist()
        {
            if (LazyDictionary.TryGetValue("lindexi", out var foo))
            {
                _foo = foo;
            }
        }

        [Benchmark]
        public void ContainGetExist()
        {
            if (LazyDictionary.ContainsKey("lindexi"))
            {
                _foo = LazyDictionary["lindexi"];
            }
        }


        [Benchmark]
        public void TryGetNoExist()
        {
            if (LazyDictionary.TryGetValue("lindexi123", out var foo))
            {
                _foo = foo;
            }
        }

        [Benchmark]
        public void ContainGetNoExist()
        {
            if (LazyDictionary.ContainsKey("lindexi123"))
            {
                _foo = LazyDictionary["lindexi123"];
            }
        }

        private object _foo;

        private Dictionary<string, object> LazyDictionary { get; } = new Dictionary<string, object>();

    }

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