Ok, since there wasnt any replies to this post, I will try to answer your question as completly as possible, giving a few options and ideas for you to toy around with.

To make a long story short, DBI::Proxyserver is a module that allows you to become a proxy server for databases. IE your database requests are sent not to your real database, but to an intermediary machine with this module (along with socket code etc..).

As with a any other proxy server, all it does is take requests, interpret them, and redirect as rules specify. The keyword here is rules. With DBI::Proxyserver there is a "configuration" section, which entails the 'accept' paremeter.
if accept param here was set to a maximum of 10 connections that can be queued, anything above that will be thrown out.

Still, in order to utilize the DBI::Proxyserver, you will have to use the DBI::Proxy module, which understands how the DBI::Proxyserver interprets requests.

Another, and in my eyes, a more suitable and cheaper solution to your problem is to use fork() to "hold back" connections that your program might make..For example:

#!/usr/local/bin/perl

# How many conncurrent connections do we want to make?
$MAXCHILD = 10;

@pids;
$npids = 0;
for ($i = 0; $i<$MAXCHILD;$i++) {
 my $pid;
 $pid=fork();
 if($pid>0){
  $npids++;
   if($npids>=$MAXCHILD){
    for(1..($MAXCHILD)){
     $wait_ret=wait();
     if($wait_ret>0){
      $npids--;
     }
    }
   }
   next;
  }  
  elsif(undef $pid) {
   exit(0);
  }
  else {
   CALL_YOUR_DBI_ROUTINE_HERE();
   exit(0);
  } 
  exit(0);
 } 
 for(1..$npids){
  $wt=wait();
  if($wt==-1){
   redo;
 }
}
[download]

Erm...I think thats right. (I have a directory with snippets of useful code Ive used in other programs, and I tailored this one a little just for this example without testing heheh =P)

A third and final thing you could do that I can think of is fine tune your acctuall database options. I know there are maxconnection options in mysql,msql,oracle, but I dont know the exact syntax off hand, but I do know they are pretty well bluntly stated in the documentation. I hope I helped in some little way.

-cleen