[darcs-users] darcs changes --maxcount=1

[Gwern Branwen]

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So one of my earnest desires for improving Gitit performance on
test.darcs.net was to remove as many calls to darcs changes as
possible in Gitit & Filestore (finished in HEAD), and also for 'darcs
changes' to be much faster for the use-case of getting the last hash
affecting a given file.

The latter seems to've been done during the Darcs sprint, and the
- --max-count option is now available at the branch
http://code.haskell.org/darcs/sprint-2009-04/max-count

It offers a considerable speedup: example timings on my system include

AlexanderGrafov.page
real	0m0.150s
user	0m0.124s
sys	0m0.020s

AnttiJuhaniKaijanaho.page
real	0m0.150s
user	0m0.128s
sys	0m0.020s

Backups.page
real	0m0.120s
user	0m0.092s
sys	0m0.020s

A comparable command, dropping the max-count, is noticeably slower:

AlexanderGrafov.page
real	0m3.320s
user	0m1.188s
sys	0m0.220s

AnttiJuhaniKaijanaho.page
real	0m1.011s
user	0m0.892s
sys	0m0.120s

Backups.page
real	0m9.653s
user	0m1.380s
sys	0m0.236s

enWheeler.page
real	0m1.272s
user	0m1.032s
sys	0m0.212s

BestPractices.page
real	0m1.947s
user	0m1.652s
sys	0m0.264s

Binaries.page
real	0m2.102s
user	0m1.480s
sys	0m0.228s

And even on my speedy personal system the speedup in a gitit instance
is perceptible; so I think with all these optimizations put together,
test.darcs.net may be usable again. Attached are patches that make
filestore use --max-count=1 (due to versioning you may need to
override the darcs dependency).

- --
gwern
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