You could simplify your data structures by using separate hashes for per-iteration and accumulated data. Then you would write

    $vips{$2}++;
    ...
    push @{$vipstack{$k}}, $vips{$k};
    shift @{$vipstack{$k}} if @{$vipstack{$k}} > 50;
    ...
    my $temp = $vipstack{$k};
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#5. You aren't using strict.

#!/usr/bin/perl

use strict; 
use simplegraph;

$iteration = 0;

$servers={'64.210.209.50' => { domain => 'www.zwire.com',
                               scale => 3500,
                               vips => [],
                              },
          '64.210.209.51' => {},
         };
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splice (@{$vips{$k}{'stack'}},0,$#{$vips{$k}{'stack'}}-50) if ($#{$vip
+s{$k}{'stack'}}>50);
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Well cooked!  Oddly enough, all you need is:    splice @{$vips{$k}{'stack'}}, 0, -50; It will leave the array untouched if it is not greater than 50.

$ perldoc -f splice
   . . .
   If LENGTH is negative, leaves that many elements off the end of the
+ array.
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(I guess they mean "off the deleted array" -- at all events, that's how it works (and also what makes sense).  It's explained clearly here!)

  p

Update: As dws points out below, I completly missed the hash growth problem. I added a line below to deal with that (and corrected my obligatory typo also pointed out to me by dws Thanks!)

I didn't think that there was too much wrong with your data structures. You could squash the 3 hashes into 1 but they seem okay as they are. Actually I didn't see to much wrong at all with your code, though I do use warning and strict religously, they aren't obligatory. You really should be checking the return codes from your backtick commands, I left this as comments as I don't know what values would be correct for those two programs. You could probably recode the ... unless $? == 0 to be ... if $?; but you'll need to check the docs for the right values.

Given your code as a starting point there are a few things that I would do differently but most of them are a matter of taste rather than any real benefit.

I offer my lightly reworked version of your code which you may or may not find useful.

#!/usr/bin/perl -w
use strict;
#use simplegraph;

my %vips = ();
# Set the graph max scale per server
my %scale = (
    '64.210.209.50' => 3500,
    '64.210.209.51' => 2000,
    '64.210.209.54' => 3500,
    '64.210.209.56' => 100,
    '64.210.209.61' => 3000,
    '64.210.209.132' => 500
);

# Set VIPs -> names mapping
my %name = (
    '64.210.209.50' => 'www.zwire.com',
    '64.210.209.51' => 'www.adquest3d.com',
    '64.210.209.54' => 'bannerads.zwire.com',
    '64.210.209.56' => 'sitemanager.zwire.com',
    '64.210.209.61' => 'imagesource.zwire.com',
    '64.210.209.132' => 'www.carcast.com',
);

my $re_ip = qr/(\d+\.\d+\.\d+\.\d+):\d+/;
my $re_line = qr/ ^ \s* $re_ip \s* -> \s* $re_ip \s* -> \s* $re_ip /x;

my $iteration = 0;

# Loop forever
do {
    $iteration++;
    # Reset data
    my @connections = `bigpipe conn dump`;

    # You'll have to check docs for bigpipe to decide what constitutes
+ a failure code
#    warn "bigpipe failed with rc:$?\n" and next unless $? >> 8 == 0; 
+# or whatever

    foreach my $line (@connections) {
        $vips{$2}{$iteration}++ if ($line =~ /$re_line/);
    }
    # Push our new data onto the stack, but remove from the queue if w
+e have more than 50
    foreach my $k (keys %vips) {
        push  @{$vips{$k}{'stack'}}, $vips{$k}{$iteration};
        shift @{$vips{$k}{'stack'}} if $#{$vips{$k}{'stack'}} > 50;
            ## THIS LINE SHOULD BE ADDED!! See [dws]'s post below.
        delete $vips{$k}{$iteration}; 
    }
    # Make a graph for each VIP
    foreach my $k (keys %vips) {
        # Skip VIPs that aren't in %name, we don't care about them
        next unless $name{$k};

        my $image = SimpleGraph->new(
            width             => 230,
            height             => 120,
            yscale             => $scale{$k},
            marginwidth     => 5,
            borderright     => 5,
            borderleft         => 30,
            gridlabels         => 'yes',
            gridlines         => ($scale{$k} / 4),
            label             => $name{$k}." connections",
        );

        $image->PlotSeries( color => "0,0,255", data  => $vips{$k}{'st
+ack'} );

        $image->Draw(       file  => "/usr/local/www/local/connections
+$k.tmp" );

        `mv -f /usr/local/www/local/connections$k.tmp /usr/local/www/l
+ocal/connections$k.gif`;
#        warn "mv failed with rc:$?\n" unless $? >> 8 == 0; # or whate
+ver?
    }
} while(sleep 10);
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I didn't think that there was too much wrong with your data structures.

Then how does $vips{$k}{$iteration} ever get deleted when $iteration moves on to $iteration++ ? Looks like out-of-control HoH growth to me.