From: Johannes Schindelin <Johannes.Schindelin@gmx.de>
To: Tony Finch <dot@dotat.at>
Cc: Linus Torvalds <torvalds@linux-foundation.org>, git@vger.kernel.org
Subject: Re: Newton-Raphson, was Re: Performance issue of 'git branch'
Date: Fri, 24 Jul 2009 01:24:21 +0200 (CEST) [thread overview]
Message-ID: <alpine.DEB.1.00.0907240114410.8306@pacific.mpi-cbg.de> (raw)
In-Reply-To: <alpine.LSU.2.00.0907232310220.22113@hermes-2.csi.cam.ac.uk>
Hi,
On Thu, 23 Jul 2009, Tony Finch wrote:
> I think Newton-Raphson is a brilliant but misleading idea. (As Junio
> said, "egg of Columbus" - it certainly blew my mind!) However, Newton's
> method works with smooth curves, but a pack index is a straight line
> plus stochastic deviations. If you try to apply Newton's method then the
> more you zoom in the more the random variations will send you away from
> the place you want to be.
No.
Think about it, absent any further information than "it is a hash, i.e.
distributed pretty equally in _any_ byte", even subsets of a sorted list
will me more or less linear. And assuming that they are linear is _still_
your best bet.
Assuming that subsets of said sorted list will _still_ minimize the
average number of steps to take until you find the correct entry.
Unless you have more information about the nature of the hashes, of
course.
> This should give you O(1) seeks in the index per object lookup.
There is no way to achieve that, best thing you can hope for is _expected_
O(1) (e.g. with a hashmap, with exponential worst case).
Ciao,
Dscho
next prev parent reply other threads:[~2009-07-23 23:24 UTC|newest]
Thread overview: 73+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-07-22 23:59 Performance issue of 'git branch' Carlos R. Mafra
2009-07-23 0:21 ` Linus Torvalds
2009-07-23 0:51 ` Linus Torvalds
2009-07-23 0:55 ` Linus Torvalds
2009-07-23 2:02 ` Carlos R. Mafra
2009-07-23 2:28 ` Linus Torvalds
2009-07-23 12:42 ` Jakub Narebski
2009-07-23 14:45 ` Carlos R. Mafra
2009-07-23 16:25 ` Linus Torvalds
2009-07-23 1:22 ` Carlos R. Mafra
2009-07-23 2:20 ` Linus Torvalds
2009-07-23 2:23 ` Linus Torvalds
2009-07-23 3:08 ` Linus Torvalds
2009-07-23 3:21 ` Linus Torvalds
2009-07-23 17:47 ` Tony Finch
2009-07-23 18:57 ` Linus Torvalds
2009-07-23 22:48 ` Newton-Raphson, was " Tony Finch
2009-07-23 23:24 ` Johannes Schindelin [this message]
2009-07-23 23:50 ` Tony Finch
2009-07-24 0:43 ` Johannes Schindelin
2009-07-23 3:18 ` Carlos R. Mafra
2009-07-23 3:27 ` Carlos R. Mafra
2009-07-23 3:40 ` Carlos R. Mafra
2009-07-23 3:47 ` Linus Torvalds
2009-07-23 4:10 ` Linus Torvalds
2009-07-23 5:13 ` Junio C Hamano
2009-07-23 5:17 ` Carlos R. Mafra
2009-07-23 4:40 ` Junio C Hamano
2009-07-23 5:36 ` Linus Torvalds
2009-07-23 5:52 ` Junio C Hamano
2009-07-23 6:04 ` Junio C Hamano
2009-07-23 17:19 ` Linus Torvalds
2009-07-23 16:07 ` Carlos R. Mafra
2009-07-23 16:19 ` Linus Torvalds
2009-07-23 16:53 ` Carlos R. Mafra
2009-07-23 19:05 ` Linus Torvalds
2009-07-23 19:13 ` Linus Torvalds
2009-07-23 19:55 ` Carlos R. Mafra
2009-07-24 20:36 ` Linus Torvalds
2009-07-24 20:47 ` Linus Torvalds
2009-07-24 21:21 ` Linus Torvalds
2009-07-24 22:13 ` Linus Torvalds
2009-07-24 22:18 ` david
2009-07-24 22:42 ` Linus Torvalds
2009-07-24 22:46 ` david
2009-07-25 2:39 ` Linus Torvalds
2009-07-25 2:53 ` Daniel Barkalow
2009-08-07 4:21 ` Jeff King
2009-07-24 22:54 ` Theodore Tso
2009-07-24 22:59 ` Shawn O. Pearce
2009-07-24 23:28 ` Junio C Hamano
2009-07-26 17:07 ` Avi Kivity
2009-07-26 17:16 ` Johannes Schindelin
2009-07-24 23:46 ` Carlos R. Mafra
2009-07-25 0:41 ` Carlos R. Mafra
2009-07-25 18:04 ` Linus Torvalds
2009-07-25 18:57 ` Timo Hirvonen
2009-07-25 19:06 ` Reece Dunn
2009-07-25 20:31 ` Mike Hommey
2009-07-25 21:02 ` Linus Torvalds
2009-07-25 21:13 ` Linus Torvalds
2009-07-25 23:23 ` Johannes Schindelin
2009-07-26 4:49 ` Linus Torvalds
2009-07-26 16:29 ` Theodore Tso
2009-07-26 7:54 ` Mike Hommey
2009-07-26 10:16 ` Johannes Schindelin
2009-07-26 10:23 ` demerphq
2009-07-26 10:27 ` demerphq
2009-07-25 21:04 ` Carlos R. Mafra
2009-07-23 16:48 ` Anders Kaseorg
2009-07-23 19:03 ` Carlos R. Mafra
2009-07-23 0:23 ` SZEDER Gábor
2009-07-23 2:25 ` Carlos R. Mafra
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