Specific version requirements for xxhash vs. xxh64 library

[frispete]

Hi,

while the whole world is waiting for Borg 2.0 to appear, I'm trying to provide 1.1.6 for older openSUSE distributions, where I stumbled upon a question, that isn't covered as far as I was reading...

Given, the openSUSE distribution has xxhash 0.6.5 available, is it recommended to use this, attempt to update that to 0.8.0 or just prefer to use the builtin xxh64 0.8.0 for that case?

While at it, between xxhash 0.6.5 and 0.8.0, significant algorithmic changes were done. Does that has a chance to break any (existing) backups in any way?

[ThomasWaldmann]

This is from 1.1-maint branch, setup.py:

# True: use the shared libxxhash (>= 0.6.5 [>= 0.7.2 on ARM]) from the system, False: use the bundled xxhash code
prefer_system_libxxhash = True

So, IIRC, 0.6.5 should be fine IF you are not on ARM.

Otherwise you could set above to False and it would use the bundled xxhash code, which is currently 0.7.4.

[frispete]

Thanks, Thomas, much appreciated.

Do you remember the issue with ARM? We have ARM targets of course.

Would it pick up xxh64 automatically, if it cannot locate any xxhash libs?

[ThomasWaldmann]

iirc, on ARM there was a memory access alignment issue, so it crashed with a cpu exception before the xxh64 code was fixed.
just search the issue tracker here or there...

iirc you need to set the flag in setup.py to tell what you want.

[ThomasWaldmann]

borg uses XXH64 to compute file integrity checksum, e.g. for its indexes and caches.

So guess the worst thing that could happen IF the xxh64 algorithm would change, yielding different hash values for same content, is that you'ld need to drop and recreate the caches/indexes.

[frispete]

Thanks, Thomas, this information is very helpful..