How we did (and did not) improve performance and efficiency in Marten 2.0

Marten 2.0 was released yesterday, and one of the improvements is somewhat significantly runtime performance and far better memory utilization in applications that use Marten. For today’s blog post, here’s what we did and tried to get there:

• Avoiding Json strings whenever possible. Some time last year Ayende wrote a “review” of Marten on his blog before almost immediately retracting it. While I didn’t agree with most of his criticisms, he did call out Marten for being inefficient in its Json serialization by reading and writing the full Json strings instead of opting for more efficient mechanisms of reading or writing via byte arrays or Stream’s. The “write” side of this problem was largely solved in Marten 2.0, but after some related changes in the underlying Npgsql library, the “read” side of Marten uses TextReader’s as the input to Json serialization, therefore bypassing the need to create then immediately tear down string objects. These changes reduced the memory allocations in Marten almost by half, with maybe a 15-20% improvement in performance.
• StringBuilder for all SQL command build up. I know what you’re thinking, “duh, StringBuilder is way more efficient than string concatenation,” but Marten got off the ground by mostly using string interpolation and concatenation. For 2.0, I went back over all that code and switched to StringBuilder’s, which has the nice impact of reducing memory utilization quite a bit (it didn’t make that much difference in performance). I absolutely don’t regret starting with simpler, cruder mechanisms to get things working before pulling in this optimization.
• FastExpressionCompiler – Marten heavily uses dynamically generated Expression’s that are then compiled to Func or Action’s for document persistence and loading. The excellent FastExpressionCompiler library from Maksim Volkau replaces the built in Expression compilation with a new model that results both in delegates that are faster in runtime, and also reduces the compilation time of these expressions. Using FastExpressionCompiler makes Marten bootstrap faster, which made a huge improvement in Marten’s test suite execution. I measured about a 10% throughput performance in Marten’s benchmarks just by using this library
• Newtonsoft.Json 9 to 10 and back to 9 – Newtonsoft.Json 10 was measurably slower in the Marten benchmarks, so we reverted back to 9.0.1. Bummer. You can always opt for Jil or other alternatives for considerably faster json serialization, but we found too many cases where Jil errored out on document types that Newtonsoft.Json handled just fine, so we stuck with Newtonsoft as the default based on the idea that the code should at least work;)

What’s left to do for performance?

• I’m sure we could get better with our mechanics for byte[] or char[] pooling and probably some buffering in the ADO.Net manipulation during async methods
• We know there are some places where the Linq provider generates Sql that isn’t as efficient as it could be. We might try to tackle this tactically in use case by use case, but I’m hoping for the version of Postgresql after 10 to get their improved Json querying functionality based on JsonPath before we do anything big to the Linq support.