[indygreg2]

It depends on the "window size" used by the compressor. According to https://github.com/facebook/zstd/blob/dev/doc/zstd_compressi..., the window size can be anywhere from 1KB to 1.875TB.

The table mapping compression levels to window sizes is at https://github.com/facebook/zstd/blob/15a7a99653c78a57d1ccbf.... The first element is the window size. I'm pretty sure you raise 2 to that power to get the window size. As you can see, level 1 is 2^18, which is 256KB - far larger than the minimum of 1KB. Lowering it will make compression faster at the expense of compression ratio.

For comparison, zlib's max window size is 32KB. That's one reason its compression ratio is so limited.