From: Jeff Garzik <jgarzik@pobox.com>
To: Git Mailing List <git@vger.kernel.org>,
Linus Torvalds <torvalds@osdl.org>
Subject: Hash collision count
Date: Sat, 23 Apr 2005 16:27:47 -0400 [thread overview]
Message-ID: <426AAFC3.800@pobox.com> (raw)
Ideally a hash + collision-count pair would make the best key, rather
than just hash alone.
A collision -will- occur eventually, and it is trivial to avoid this
problem:
$n = 0
attempt to store as $hash-$n
if $hash-$n exists (unlikely)
$n++
goto restart
key = $hash-$n
Tangent-as-the-reason-I-bring-this-up:
One of my long-term projects is an archive service, somewhat like
Plan9's venti: a multi-server key-value database, with sha1 hash as the
key.
However, as the database grows into the terabyte (possibly petabyte)
range, the likelihood of a collision transitions rapidly from unlikely
-> possible -> likely.
Since it is -so- simple to guarantee that you avoid collisions, I'm
hoping git will do so before the key structure is too ingrained.
Jeff
next reply other threads:[~2005-04-23 20:23 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-04-23 20:27 Jeff Garzik [this message]
2005-04-23 20:33 ` Hash collision count Jeff Garzik
2005-04-23 23:00 ` Ray Heasman
2005-04-23 23:20 ` Jeff Garzik
2005-04-23 23:46 ` Petr Baudis
2005-04-24 0:35 ` Jeff Garzik
2005-04-24 0:40 ` Petr Baudis
2005-04-24 0:43 ` Jeff Garzik
2005-04-24 21:24 ` Imre Simon
2005-04-24 22:25 ` Whales falling on houses - was: " Jon Seymour
2005-04-25 23:50 ` Tom Lord
2005-04-26 0:00 ` Petr Baudis
2005-04-24 1:01 ` Ray Heasman
2005-04-24 7:56 ` David Lang
-- strict thread matches above, loose matches on Subject: below --
2005-04-24 23:16 linux
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