Performance considerations for logging

Filtering happens after construction

emit creates a complete Event before checking whether any filtering would discard it. Events are reasonably cheap to construct, because all capturing borrows from locals, but applications may want to use their own compile-time filtering if emission becomes expensive.

Static runtimes avoid dynamic dispatch

emit uses an ambient, dynamically typed runtime by default. You can generally improve performance by using an explicitly specified static runtime instead. See Configuring a static runtime for details.