[darcs-users] no more checkpoints, but hashed repos for GHC in Darcs 2.4?

Petr Rockai me at mornfall.net
Thu Sep 17 16:40:11 UTC 2009


Eric Kow <kowey at darcs.net> writes:

>>   - http://bugs.darcs.net/issue1589 (7-second overhead for pulling
>>     or unpulling one patch)
>
> This one still needs attention.
>
> We've pretty much verified that this is slow with hashed repositories
> and fast with old-fashioned repositories.  OK one second comes from the
> deliberate delay and maybe the extra 6 comes from needless inventory
> optimisation?
I'll look at it. It may as well be that we are calling clean_hashdir, which is
very slow, especially with large cache (and although I made it a lot faster in
darcs-hs, it'll still take much longer than the equivalent operation in
old-fashioned, which is nil).

>>   - timestamps getting out of sync by hard-linking the hashed pristine files.
>>     I presume this is fixed by darcs-hs anyway.
>
> I believe that for projects with branches, fixing this is where the
> biggest positive impact from hashed-storage will be (Rah!).
>
>>   - dividing the cache into subdirectories to avoid bad filesystem
>>     performance with large directories.
>
> That's http://bugs.darcs.net/issue1536 :-)
>
> Petr: how do you feel about this?  Do you rate this as being easier
> than packs?  Is it realistic to want this in Darcs 2.4?  I am also
> concerned about backward compatibility.  How do we handle this?  Format
> change?
For cache, this should be quite simple. For repos, this would be incompatible
change and we probably can't afford to do it just yet.

Yours,
   Petr.


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