Performance issue: comparing to String.Format

Question

A while back a post by Jon Skeet planted the idea in my head of building a CompiledFormatter class, for using in a loop instead of String.Format().

Answer 1

Here's the final result:

I changed the format string in a benchmark trial to something that should favor my code a little more:

The quick brown {0} jumped over the lazy {1}.

As I expected, this fares much better compared to the original; 2 million iterations in 5.3 seconds for this code vs 6.1 seconds for String.Format. This is an undeniable improvement. You might even be tempted to start using this as a no-brainer replacement for many String.Format situations. After all, you'll do no worse and you might even get a small performance boost: as much 14%, and that's nothing to sneeze at.

Except that it is. Keep in mind, we're still talking less than half a second difference for 2 million attempts, under a situation specifically designed to favor this code. Not even busy ASP.Net pages are likely to create that much load, unless you're lucky enough to work on a top 100 web site.

Most of all, this omits one important alternative: you can create a new StringBuilder each time and manually handle your own formatting using raw Append() calls. With that technique my benchmark finished in only 3.9 seconds. That's a much greater improvement.

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In summary, if performance doesn't matter as much, you should stick with the clarity and simplicity of the built-in option. But when in a situation where profiling shows this really is driving your performance, there is a better alternative available via StringBuilder.Append().