JVM profiler indicates checksums as implemented are a significant bottleneck.
impl.RawOutput wraps the provided OutputStream with a CheckedOutputStream. Every time a rawInt is written, CheckedOutputStream calls on its checksum to update itself.
Adler32's update method happens to be native, which may not be germane to the problem.
The read side of data.fressian already exposes a knob for checksums to be ignored in RawInput. No such knob exists on the write side.
Checksums are used in the footer methods. They may be extremely useful for data at rest, but may be redundant with other out-of-band mechanisms.
Buffering so that checksums don't recalculate frequently.
Exposing a knob to control whether write checksums are enabled. This would potentially involve changes with the footer.