Author: david
Date: Mon Dec 6 16:20:52 2010
New Revision: 8874
Log:
MySQL primary key uniqueness is case-insensitive. Use only lower-case letters
in permalink hash.
Modified:
trunk/lib/model/QubitSlug.php
Modified: trunk/lib/model/QubitSlug.php
==============================================================================
--- trunk/lib/model/QubitSlug.php Mon Dec 6 00:02:21 2010 (r8873)
+++ trunk/lib/model/QubitSlug.php Mon Dec 6 16:20:52 2010 (r8874)
@@ -23,22 +23,20 @@
{
$slug = null;
- $alphabet =
'0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
+ $alphabet = '0123456789abcdefghijklmnopqrstuvwxyz';
- // Probability of collision is approximately the number of rows in slug
- // table over getrandmax(), so the probability increases with the number
- // of rows
+ // Probability of generating a collision can be found using this formula
+ //
http://en.wikipedia.org/wiki/Birthday_paradox#Cast_as_a_collision_problem
//
- // More accurately, probability is number of slugs containing only digits
- // and letters over getrandmax() - but this is most slugs
- //
- // For constant probability and increasing slug length, COUNT() the slug
- // table, but then it'd be better to use an SQL expression for the slug
+ // For getrandmax() = 2^31-1 (32-bit signed integer max) probability of
+ // collision is >50% when we reach approx. 50,000 records
$rand = rand();
- while (62 < $rand)
+
+ // Convert $rand to base36 hash
+ while (36 < $rand)
{
- $slug .= $alphabet[$rand % 62];
- $rand /= 62;
+ $slug .= $alphabet[$rand % 36];
+ $rand /= 36;
}
return $slug;
--
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