view CONTRIBUTORS @ 23097:30124c40d11f stable

util.fspath: use a dict rather than a linear scan for lookups

Previously, we'd scan through the entire directory listing looking for a
normalized match.  This is O(N) in the number of files in the directory. If we
decide to call util.fspath on each file in it, the overall complexity works out
to O(N^2). This becomes a problem with directories a few thousand files or
larger.

Switch to using a dictionary instead. There is a slightly higher upfront cost
to pay, but for cases like the above this is amortized O(1). Plus there is a
lower constant factor because generator comprehensions are faster than for
loops, so overall it works out to be a very small loss in performance for 1
file, and a huge gain when there's more.

For a large repo with around 200k files in it on a case-insensitive file
system, for a large directory with over 30,000 files in it, the following
command was tested:

ls | shuf -n $COUNT | xargs hg status

This command leads to util.fspath being called on $COUNT files in the
directory.

COUNT  before  after
    1   0.77s  0.78s
  100   1.42s  0.80s
 1000    6.3s  0.96s

I also tested with COUNT=10000, but before took too long so I gave up.

[This file is here for historical purposes, all recent contributors
should appear in the changelog directly]

Andrea Arcangeli <andrea at suse.de>
Thomas Arendsen Hein <thomas at intevation.de>
Goffredo Baroncelli <kreijack at libero.it>
Muli Ben-Yehuda <mulix at mulix.org>
Mikael Berthe <mikael at lilotux.net>
Benoit Boissinot <bboissin at gmail.com>
Brendan Cully <brendan at kublai.com>
Vincent Danjean <vdanjean.ml at free.fr>
Jake Edge <jake at edge2.net>
Michael Fetterman <michael.fetterman at intel.com>
Edouard Gomez <ed.gomez at free.fr>
Eric Hopper <hopper at omnifarious.org>
Alecs King <alecsk at gmail.com>
Volker Kleinfeld <Volker.Kleinfeld at gmx.de>
Vadim Lebedev <vadim at mbdsys.com>
Christopher Li <hg at chrisli.org>
Chris Mason <mason at suse.com>
Colin McMillen <mcmillen at cs.cmu.edu>
Wojciech Milkowski <wmilkowski at interia.pl>
Chad Netzer <chad.netzer at gmail.com>
Bryan O'Sullivan <bos at serpentine.com>
Vicent Seguí Pascual <vseguip at gmail.com>
Sean Perry <shaleh at speakeasy.net>
Nguyen Anh Quynh <aquynh at gmail.com>
Ollivier Robert <roberto at keltia.freenix.fr>
Alexander Schremmer <alex at alexanderweb.de>
Arun Sharma <arun at sharma-home.net>
Josef "Jeff" Sipek <jeffpc at optonline.net>
Kevin Smith <yarcs at qualitycode.com>
TK Soh <teekaysoh at yahoo.com>
Radoslaw Szkodzinski <astralstorm at gorzow.mm.pl>
Samuel Tardieu <sam at rfc1149.net>
K Thananchayan <thananck at yahoo.com>
Andrew Thompson <andrewkt at aktzero.com>
Michael S. Tsirkin <mst at mellanox.co.il>
Rafael Villar Burke <pachi at mmn-arquitectos.com>
Tristan Wibberley <tristan at wibberley.org>
Mark Williamson <mark.williamson at cl.cam.ac.uk>