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List:       php-db
Subject:    RE: [PHP-DB] generating unique id's
From:       "Vicky Atkinson" <vicky.atkinson () clearink ! com>
Date:       2000-06-30 15:55:45
[Download RAW message or body]

If you're really paranoid about possible duplicate values, you can use your
database to store one seed value.  Then each time you need to get a unique
identifier, you lock the table with the seed, pull it out, use it to
generate a new random number, then put that number back in as the seed and
unlock the table.  You can use the random number to generate your unique
identifier (string or number).  That way even if you're running a site on
multiple Web servers and people request IDs at the same instant, they won't
get the same IDs.  Of course this is a hit to the database, and you lock up
a table, but that may be worth it to you if it's important to have truly
unique ID values.

Vicky

-----Original Message-----
From: Edward Wong [mailto:wyuanzheng@21cn.com]
Sent: Tuesday, June 29, 1999 7:14 PM
To: Cody Caughlan; php-db@lists.php.net
Subject: Re: [PHP-DB] generating unique id's


Hi:

I use the following code:

<?
for ($i = 0; $i < 5; $i++) {
 mt_srand((double)microtime()*1000000);
 $randval[$i] = mt_rand();
}

for ($i = 0; $i < 5; $i++) {
 echo $randval[$i],"<BR>";
}
?>

or

<?
// Method 2
mt_srand((double)microtime()*1000000);
ECHO "<FONT COLOR=RED>";
for ($i = 0; $i < 5; $i++) {
 $randval[$i] = mt_rand();
}

for ($i = 0; $i < 5; $i++) {
 echo $randval[$i],"<BR>";
}
ECHO "</FONT>";
?>


and the result is:

122653537
849966493
749620674
706811529
86123690

2074739843
1867927643
1706046782
1795463355
1221802180

Any one can meet your needs, you see.
If you can't, maybe your computer is too good. :-)


-------------------------------------
#       Edward Wong                 #
#                                   #
# E-Mail:wyuanzheng@21cn.com        #
# Phone: 86-21-63615261 * 207       #
#                                   #
# iSpaceBank Group, Shanghai, China #
#                                   #
-------------------------------------
----- Original Message -----
From: "Cody Caughlan" <codyc@cisco.com>
To: <php-db@lists.php.net>
Sent: Thursday, June 29, 2000 6:10 AM
Subject: [PHP-DB] generating unique id's


> Hello,
>
> I need to generate a unique id. The problem I am running into is this:
> I have a for loop that generates a bunch of id's using the time()
> function, the problem is that since the for loop only takes less than a
> microsecond, and the precision of the time() function is a microsecond,
> all the id's are the same. I looked into using uniqid(), which according
> to the PHP manual generates an INT. However, I tested it out, and in a
> microsecond it DOES generate a series of different, random STRINGS, mix of
> ints and characters, NOT an INT, which like I said is what the PHP manual
> uses. MySQL requires that the primary key be an INT, so I can use uniqid()
> function to generate this id, because its a string.
>
> What can I do?
>
> In summary, generate a whole list of unique INTEGER id's in under a
> microsecond...
>
> Thanks
> /Cody Caughlan
>
>
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