view CONTRIBUTORS @ 25647:46a96dd4d976

revset: improves time complexity of 'roots(xxx)'

The canonical way of doing 'roots(X)' is 'X - children(X)'. This is what the
implementation used to be. However, computing children is expensive because it
is unbounded. Any changesets in the repository may be a children of '0' so you
have to look at all changesets in the repository to compute children(0).
Moreover the current revsets implementation for children is not lazy, leading to
bad performance when fetching the first result.


There is a more restricted algorithm to compute roots:

    roots(X) = [r for r in X if not parents(r) & X]

This achieve the same result while only looking for parent/children relation in
the X set itself, making the algorithm 'O(len(X))' membership operation.
Another advantages is that it turns the check into a simple filter, preserving
all laziness property of the underlying revsets.

The speed is very significant and some laziness is restored.

-) revset without 'roots(...)' to compare to base line
0) before this change
1) after this change

revset #0: roots((tip~100::) - (tip~100::tip))
   plain         min           last
-) 0.001082      0.000993      0.000790
0) 0.001366      0.001385      0.001339
1) 0.001257  92% 0.001028  74% 0.000821  61%

revset #1: roots((0::) - (0::tip))
   plain         min           last
-) 0.134551      0.144682      0.068453
0) 0.161822      0.171786      0.157683
1) 0.137583  85% 0.146204  85% 0.070012  44%

revset #2: roots(tip~100:)
   plain         min           first         last
-) 0.000219      0.000225      0.000231      0.000229
0) 0.000513      0.000529      0.000507      0.000539
1) 0.000463  90% 0.000269  50% 0.000267  52% 0.000463  85%

revset #3: roots(:42)
   plain         min           first         last
-) 0.000119      0.000146      0.000146      0.000146
0) 0.000231      0.000254      0.000253      0.000260
1) 0.000216  93% 0.000186  73% 0.000184  72% 0.000244  93%

revset #4: roots(not public())
   plain         min           first
-) 0.000478      0.000502      0.000504
0) 0.000611      0.000639      0.000634
1) 0.000604      0.000560  87% 0.000558

revset #5: roots((0:tip)::)
   plain         min           max           first         last
-) 0.057795      0.004905      0.058260      0.004908      0.038812
0) 0.132845      0.118931      0.130306      0.114280      0.127742
1) 0.111659  84% 0.005023   4% 0.111658  85% 0.005022   4% 0.092490  72%

revset #6: roots(0::tip)
   plain         min           max           first         last
-) 0.032971      0.033947      0.033460      0.032350      0.033125
0) 0.083671      0.081953      0.084074      0.080364      0.086069
1) 0.074720  89% 0.035547  43% 0.077025  91% 0.033729  41% 0.083197

revset #7: 42:68 and roots(42:tip)
   plain         min           max           first         last
-) 0.006827      0.000251      0.006830      0.000254      0.006771
0) 0.000337      0.000353      0.000366      0.000350      0.000366
1) 0.000318  94% 0.000297  84% 0.000353      0.000293  83% 0.000351

revset #8: roots(0:tip)
   plain         min           max           first         last
-) 0.002119      0.000145      0.000147      0.000147      0.000147
0) 0.047441      0.040660      0.045662      0.040284      0.043435
1) 0.038057  80% 0.000187   0% 0.034919  76% 0.000186   0% 0.035097  80%

revset #0: roots(:42 + tip~42:)
   plain         min           max           first         last          sort
-) 0.000321      0.000317      0.000319      0.000308      0.000369      0.000343
0) 0.000772      0.000751      0.000811      0.000750      0.000802      0.000783
1) 0.000632  81% 0.000369  49% 0.000617  76% 0.000358  47% 0.000601  74% 0.000642  81%

[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>