[darcs-users] Is darcs optimize --compress still useful?

Trent W. Buck trentbuck at gmail.com
Tue Mar 17 23:24:48 UTC 2009

Petr Rockai <me at mornfall.net> writes:

> trentbuck at gmail.com (Trent W. Buck) writes:
>> AFAICT the only way uncompressed files would require less memory is if
>> Darcs kept both the compressed AND uncompressed copies of the file in
>> memory.  I seem to recall that this was a problem in older releases, but
>> was fixed around the 2.1 or 2.2 release.
>> That being the case, can we get rid of these options, and (eventually)
>> get rid of support for uncompressed patches altogether?

> Not really. The difference is that uncompressed patches can be mmaped,
> and are therefore more efficient than compressed (with saved space
> being on the edge of measurability, since quite many compressed
> patches take the same number of filesystem blocks as their
> uncompressed counterparts...).

So if I've understood correctly, we have *three* options (remove
compression, put it back again, and dither) in order to support
uncompressed patches -- a feature which

  - increases disk consumption considerably;
  - decreases RAM consumption negligibly; and
  - decreases CPU time negliglibly.

So I still don't see the need for this feature.  I advocate removing it
in a future release, unless someone wants to give concrete numbers where
uncompressed patches really *do* save a non-negligible amount of RAM
and/or CPU.

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