JSON serialization is a big factor in web applications, especially for applications that expose almost all their functionality over REST API as our Virto platform does, and the performance of object serialization or deserialization has a significant impact on overall application performance and responsiveness.
Starting with 2.x Virto platform versions and till to the newest 3.0-rc3 we have been using with Newtonsoft.Json .NET serializer for Web API and basically were happy with it until the last moment, on one of our projects we faced with big API response latency for big size response with 1Mb body size. The average response time was more than 10 seconds!!! and was completely unacceptable.
Digging into this problem and conduct a series of tests we end up on one suspect, it was a JSON serializer - we use Newtonsoft.Json .NET 12.0.3 that integrated into both ASP.NET versions.
Durinng investigations we found this excellent article The Battle of C# to JSON Serializers in .NET Core 3 that contains the benchmarks of six the most popular JSON serializer. But any of time charts from this article doesn’t show the big difference between Newtonsoft.Json and embedded into ASP.NET Core System.Text.Json serializers.
And to confirm our doubts we conducted our own benchmark. We created an empty pure ASP.NET Core Web API project from the templates proposed by Visual Studio 2019. Defined the one API endpoint that returned three responses with different sizes (1.6Mb, 16Mb, and 160Mb) respectively and measured response times for using Newtonsoft.Json and embedded into ASP.NET Core 3.0 System.Text.Json serializers.
Here is our benchmark
The benchmark shows that for serialization with using System.Text.Json is 10 times faster than Newtonsoft.Json library.
The answer to the question why the results of our tests for single requests are different from those described in this article, we found later in the same article.
The only surprise here is how poorly Newtonsoft.Json performed. This is probably due to the UTF-16 and UTF-8 issue. The HTTP protocol works with UTF-8 text. Newtonsoft converts this text into .NET
stringtypes, which are UTF-16. This overhead is not done in either Utf8Json or System.Text.Json , which work directly with UTF-8.
Does this mean we should all change to System.Text.Json or Utf8Json?
Answer - yes! The System.Text.Json is looking as better replacement due to this library is well supported and Microsoft will continue to invest resources and effort into System.Text.Json so we are going to get excellent support.
But before replacement, we need to ensure that migration to the new serializer won’t affect exists functionality and doesn’t introduce any breaking changes for existing logic.