Comment 144 for bug 1842320

The terrible thing with compression is how we know of no universal rule. I'm sure you can even find non-pathological cases where lz4 compresses better than zpaq (and does so 1000000 times faster). And that's without taking I/O into account (or filters).

An important thing to keep in mind here is that zstd currently uses its -1 preset while xz uses its default of -6. That means that these two tools which are often in the same ballpark are configured at vastly different compression/speed setting. What's important is that you get something that works for your setup and as I said above: we don't have a rule for optimal settings (and it's probably impossible to find one).

One last note: xz decompression speed depends on the compressed size, not uncompressed size. This means that a more-compressed file decompresses faster. This might be the same with zstd since they're related compressors but I'm not 100% sure.