view CONTRIBUTORS @ 39264:d750a6c9248d stable

scmutil: avoid quadratic membership testing (issue5969)

tr.changes['revs'] is an xrange, which has an O(n) __contains__
implementation. The `rev not in newrevs` lookup a few lines below
will therefore be O(n^2) if all incoming changesets are public.

This issue isn't present on @ because 45e05d39d9ce introduced
a custom type implementing an xrange primitive with O(1) contains
and switched tr.changes['revs'] to be an instance of that type.

We work around the problem on the stable branch by casting the
xrange to a set. This is a bit hacky because it requires allocating
memory to hold each integer in the range. But we are already
holding the full set of pulled revision numbers in memory
multiple times (such as in `tr.changes['phases']`). So this is
a relatively minor problem.

This issue has been present since the phases reporting code was
introduced in the 4.7 cycle by eb9835014d20.

This change should be reverted/ignored when stable is merged into
default.

On the mozilla-unified repository with 483492 changesets, `hg clone`
time improves substantially:

before: 1843.700s user; 29.810s sys
after:   461.170s user; 29.360s sys

[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>