sub set_column_widths {
    my $h         = shift; # reference to hash table of speeds, keyed by datetime, then by database
    my $databases = shift; # reference to hash of database names, where we will set the width values
    my $names     = shift; # ref to array of database names
                           #     (so we don't need to call keys on $databases repeatedly)
    for my $key (keys %$h){
        for my $db (@$names){
            my $l = length $h->{$key}{$db};  # get length of this item in the hash table
                                             # set column width to the widest length
            $databases->{$db} = $databases->{$db} > $l ? $databases->{$db} : $l;  
        }
    }
    for my $db (@$names){  # check the width of the database names themselves too
        my $l = length $db;
        $databases->{$db} = $databases->{$db} > $l ? $databases->{$db} : $l;  
    }
}

##</code><code>##

set_column_widths(\%h, \%db, \@db);

##</code><code>##

printf "%11s", $_ for (@db);

# replace 11 with $db{$_}, the saved width for this column, and 
# stick a space between columns

printf " %$db{$_}s", $_ for (@db);

##</code><code>##

#!/usr/bin/env perl
use 5.010; use strict; use warnings;

my %h; my %m; my %db; # per-hour hash, per-minute hash, database names

sub set_column_widths {
    my $h         = shift; # reference to hash table of speeds, keyed by datetime, then by database
    my $databases = shift; # reference to hash of database names, where we will set the width values
    my $names     = shift; # ref to array of database names
                           #     (so we don't need to call keys on $databases repeatedly)
    for my $key (keys %$h){
        for my $db (@$names){
            my $l = length $h->{$key}{$db};  # get length of this item in the hash table
                                             # set column width to the wider length
            $databases->{$db} = $databases->{$db} > $l ? $databases->{$db} : $l;  
        }
    }
    for my $db (@$names){  # check the width of the database names themselves too
        my $l = length $db;
        $databases->{$db} = $databases->{$db} > $l ? $databases->{$db} : $l;  
    }
}

while(<DATA>){
    next unless /\w/;                                # skip blank lines
    my($datetime,$database,$speed) = (split)[1,2,3];
    my $ddhhmm = substr $datetime,0,16;              # substr works well here since the lengths are static
    my $ddhh   = substr $datetime,0,13;              # this one doesn't include the minutes
    $h{$ddhh  }{$database} += $speed;                # add the speed to this hour & database
    $m{$ddhhmm}{$database} += $speed;                # add the speed to this minute & database
    $db{$database} = 1;                              # save the database name
}

my @db = sort keys %db; # sort and save database names as array since we'll be looping through them many times

# HOUR SECTION START
# calculate column widths
set_column_widths(\%h, \%db, \@db);
# print out the per-hour stats
# starting with a header line
print "Frequency Hour:\ncollectionTime";
printf " %$db{$_}s", $_ for (@db);   # print each database name as a header with dynamic width
print "\n";                          # end of line

for my $key (sort keys %h){
    print "$key ";                                # print the date/hour key
    printf " %$db{$_}s", $h{$key}{$_} for (@db);  # print the value for each database that goes with this key
    print "\n";
}
# HOUR SECTION END

# MINUTE SECTION START (using %m instead of %h)
# calculate column widths
set_column_widths(\%m, \%db, \@db);
# print out the per-minute stats
# starting with a header line
print "\nFrequency Minute:\n  collectionTime";
printf " %$db{$_}s", $_ for (@db);   # print each database name as a header with dynamic width
print "\n";                          # end of line

for my $key (sort keys %m){
    print $key;                                   # print the date/hour/minute key
    printf " %$db{$_}s", $m{$key}{$_} for (@db);  # print the value for each database that goes with this key
    print "\n";
}
# MINUTE SECTION END

__DATA__
server01: 2015-06-01T12:40:03-04:00  DB101                  10 MB/sec
server01: 2015-06-01T12:40:03-04:00  DB202                   5 MB/sec
server01: 2015-06-01T12:40:03-04:00  ASM                     2 MB/sec
server01: 2015-06-01T12:40:03-04:00  MYDB101                 2 MB/sec
server01: 2015-06-01T12:40:03-04:00  MYDB202                 5 MB/sec
server01: 2015-06-01T12:40:03-04:00  _OTHER_DB_             30 MB/sec
server01: 2015-06-01T12:41:03-04:00  DB101                   3 MB/sec
server01: 2015-06-01T12:41:03-04:00  DB202                   4 MB/sec
server01: 2015-06-01T12:41:03-04:00  ASM                     2 MB/sec
server01: 2015-06-01T12:41:03-04:00  MYDB101                 9 MB/sec
server01: 2015-06-01T12:41:03-04:00  MYDB202                 7 MB/sec
server01: 2015-06-01T12:41:03-04:00  _OTHER_DB_             50 MB/sec
server02: 2015-06-01T12:40:03-04:00  DB101                  90 MB/sec
server02: 2015-06-01T12:40:03-04:00  DB202                   9 MB/sec
server02: 2015-06-01T12:40:03-04:00  ASM                     2 MB/sec
server02: 2015-06-01T12:40:03-04:00  MYDB101                 3 MB/sec
server02: 2015-06-01T12:40:03-04:00  MYDB202                 1 MB/sec
server02: 2015-06-01T12:40:03-04:00  _OTHER_DB_             90 MB/sec
server02: 2015-06-01T12:41:03-04:00  DB101                   1 MB/sec
server02: 2015-06-01T12:41:03-04:00  DB202                   4 MB/sec
server02: 2015-06-01T12:41:03-04:00  ASM                     2 MB/sec
server02: 2015-06-01T12:41:03-04:00  MYDB101                 7 MB/sec
server02: 2015-06-01T12:41:03-04:00  MYDB202                 7 MB/sec
server02: 2015-06-01T12:41:03-04:00  _OTHER_DB_             55 MB/sec