Re: Sinister variable caching problem with rand()

Thank you everyone for helping me, I am surprised by the support our there
for mod_perl.

Cosimo sent me a quick fix to add to the startup.pl file, I have tested and
verified it. The code below works with no problems after adding:

 my $srv = Apache2::ServerUtil->server;
 $srv->push_handlers(
PerlChildInitHandler => sub { srand(time ^ $$) } );

This fix not only corrected the rand() example I posted, but fixed my root
issue that rand() represented in my test script. My actual script uses:

my $id = new String::Random;
my $num = $id->randregex('[A-Za-z0-9]{30}');

This code is in a sub in another library. For the sake of keeping it simple
I removed the use of it for my example. Luckily, String::Random must have
suffered from the same rand() problem : )

And I HIGHLY appreciate Michael Peters tip (UUID() function in mysql), I
will most likely start using that in place of my own random keys to reduce
my overhead and worries.

The reason I am not using auto_increment is because the databases exist on a
mysql cluster. The auto_increment counts would have to be maintained very
carefully with multiple servers running the same database so I opted to not
worry about it and generate completely unique keys. When a line is added in
one database it is advertised to all others, the linking between lines in
diff tables is easier this way too.

Thanks a ton gentlemen, you have saved me a great deal of time.

Anthony Esposito

On Sat, May 15, 2010 at 1:03 PM, Anthony Esposito <[email protected]
> wrote:

> In one of my programs I started to receive database errors for not having a
> unique id. I generate unique ids for each of the mysql lines that I add to
> the database. I realized that the perl variable $idNum was keeping the same
> random string for multiple executions.
>
> I created a test program to demonstrate the principle of what is happening.
>
> I have shown that the $count variable will function properly, I understand
> why and expect $idNum to work the same way. However, when $idNum =
> rand(99999999999) is used it misbehaves and starts to show the same numbers
> after enough refreshes.
>
> The code stores the random numbers in a file so I can detect them over
> multiple sessions. Within the same session a random key has never been
> generated twice.
>
> Please help, I have been working on this for 2 days and it is killing my
> progress at work.
>
> -------------------------------------------------------------------------
>
> use strict;
>
> my $idNum=0;
> my $count=0;
> for(1..10){
> my %hash;
> open(data,"<keys.txt");
> while(<data>){
> chomp;
> $hash{$_}=$_;
> }
> close(data);
>
> $idNum = rand(9999999999999);
> $count++;
> open(data2,">>keys.txt");
> print data2 "$idNum\n";
> close(data2);
>
> if ($hash{$idNum}){ print "DUPLICATE - $idNum<br>\n";}else{ print "UNIQUE
> $idNum<br>\n"; }
>
> }
>
> print "$count";
>
>