C# String Interpolation Performance

Time for a follow up to my String.Concat vs String.Format Performance post from back in 2014!

I recently found out that string interpolation is not nearly as efficient as I would have thought. I also suspected that it was just doing a string concatenation, but it is actually doing a string format. This leads to a pretty significant performance degradation; the following test runs one million iterations of each.

Number of Args	Interpolation Milliseconds	String.Format Milliseconds	String.Concat Milliseconds	String Add Milliseconds	StringBuilder Milliseconds
2	262	260	19	18	34
3	367	367	25	24	35
4	500	513	31	32	41
5	646	635	67	66	44
6	740	723	79	76	49
7	802	819	86	85	52
8	938	936	97	98	58

So, what's the lesson? Don't use string interpolation in high performance areas (such as your logger)!

Enjoy,
Tom

String.Concat vs StringBuilder Performance

Time for yet another micro-optimization!

Everyone knows that Strings are immutable in .NET, thus the StringBuilder class is very important for saving memory when dealing with manipulating large strings.

...but what about performance?

Interestingly, StringBuilder is just an all around better way to combine strings! It is more memory efficient, and less processor intensive; but not by much. Below is a comparison of performance between different ways of combine strings.

String.Concat vs String.Format Performance

Time for another micro-optimization!

When building strings it is almost always easiest to write and maintain a typical format statement. However, what is the cost of that over just concatenating strings? When building strings for cache keys (which I know are going to get called a lot) I try to use String.Concat instead of String.Format. Let's look at why!

Below is a table showing a comparison the performance difference between String.Concat and String.Format. The Y axis is the number of arguments being concatenated. The X axis is the number of milliseconds it takes to complete 100,000 runs.

Number of Args	String.Concat Milliseconds	String.Format Milliseconds	Concat Percent Faster
2	4ms	10ms	150%
3	3ms	13ms	333%
4	4ms	16ms	300%
5	12ms	21ms	75%
6	14ms	24ms	71%
7	16ms	28ms	75%
8	18ms	31ms	72%