Performance

Parse text without allocating with Span<T>

Splitting a line with string.Split creates a new string for every field. For large files, ReadOnlySpan<char> lets you parse the same data with almost no allocations.

MongoDB indexes from C#, and how to know you need one

A query that's fast with a thousand documents can scan millions in production. Here's how to create indexes from the C# driver, order their fields, and check that queries actually use them.

Faster JSON with System.Text.Json source generation

By default, System.Text.Json uses reflection to work out how to serialize your types. A source generator can do that work at compile time instead, for faster startup and trimming support.

ValueTask: when to use it and when not to

ValueTask<T> can save an allocation on hot paths. It also comes with rules that Task doesn't have, and breaking them causes bugs that are hard to trace.