I need some kind of minimal testing script that will reproduce the
problem to be able to do anything with this bug, or a reference to an
upstream perl bug.

here is a sample code that will produce this leak:
#!/usr/bin/perl

use strict;

use DBI;
use Net::SMTP;
my $debug = 0;

while (1) {
    my ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) =
localtime(time);
    $year += 1900;
    $mon++;
    my $logfilename =  "whois." . sprintf("%04d%02d%02d", $year, $mon,
$mday) . ".log";


    my $mdp = 'xxx';
    my $usager = 'xxx';
    my $DBI = "dbi:Oracle:$nom_bd";

    my $dbo = DBI -> connect ($DBI,$usager,$mdp, {  RaiseError => 1,
AutoCommit => 1  } );
    unless ($dbo) {
        sleep(10);
        next;
    }

    my $sto = $dbo->prepare( " select load_seq,operation,rgpc_no from
load_discrep order by LOAD_SEQ " );
    $sto->execute();
    my %done;
    my %pulld;
    my %allhash;
    my $in;
    my $inn;
    while (my ($load_seq, $ope, $dom_no) = $sto->fetchrow_array ) {
        $done{$load_seq} = $dom_no;
        my $compo = $dom_no . ":" . $ope;
        $allhash{$compo} = $load_seq;
        $pulld{$dom_no} = $ope;
        $in .= $load_seq . ":" . $dom_no . "-" . $ope . "\n";
        undef $load_seq;
        undef $dom_no;
        undef $ope;
        undef $compo;
    }
    my %reve;
    foreach (keys %allhash) {
        $reve{$allhash{$_}} = $_;
    }
    my @doms = keys %pulld;
    my @tot = keys %done;
    $sto->finish;

    $dbo->disconnect; $dbo=0;     # Close handler for oracle
    undef $dbo;
    sleep(1);
    undef %done;
    undef %pulld;
    undef %pulld;
    undef %allhash;
    undef $in;
    undef $inn;
    undef %reve;
    undef @doms;
    undef @tot;

    next;
}

------
this is the environment:
[root@tbr01 sb]# perl -V
Summary of my perl5 (revision 5.0 version 8 subversion 0) configuration:
  Platform:
    osname=linux, osvers=2.4.21-1.1931.2.393.entsmp,
archname=i386-linux-thread-multi
    uname='linux por'
    config_args='-des -Doptimize=-O2 -g -pipe -march=i386 -mcpu=i686
-Dmyhostname=localhost -Dperladmin=root@localhost -Dcc=gcc -Dcf_by=Red
Hat, Inc. -Dinstallprefix=/usr -Dprefix=/usr -Darchname=i386-linux
-Dvendorprefix=/usr -Dsiteprefix=/usr
-Dotherlibdirs=/usr/lib/perl5/5.8.0 -Duseshrplib -Dusethreads
-Duseithreads -Duselargefiles -Dd_dosuid -Dd_semctl_semun -Di_db
-Ui_ndbm -Di_gdbm -Di_shadow -Di_syslog -Dman3ext=3pm -Duseperlio
-Dinstallusrbinperl -Ubincompat5005 -Uversiononly
-Dpager=/usr/bin/less -isr'
    hint=recommended, useposix=true, d_sigaction=define
    usethreads=define use5005threads=undef'
 useithreads=define usemultiplicity=
    useperlio= d_sfio=undef uselargefiles=define usesocks=undef
    use64bitint=undef use64bitall=un uselongdouble=
    usemymalloc=, bincompat5005=undef
  Compiler:
    cc='gcc', ccflags ='-D_REENTRANT -D_GNU_SOURCE -DTHREADS_HAVE_PIDS
-DDEBUGGING -fno-strict-aliasing -I/usr/local/include
-D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -I/usr/include/gdbm',
    optimize='',
    cppflags='-D_REENTRANT -D_GNU_SOURCE -DTHREADS_HAVE_PIDS
-DDEBUGGING -fno-strict-aliasing -I/usr/local/include -I/usr/include/gdbm'
    ccversion='', gccversion='3.2.3 20030502 (Red Hat Linux
3.2.3-19)', gccosandvers=''
gccversion='3.2.3 200305'
    intsize=o, longsize=s, ptrsize=l, doublesize=8, byteorder=1234
    d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=12
    ivtype='long'
k', ivsize=4'
ivtype, nvtype='double'
o_no', nvsize=, Off_t='', lseeksize=8
    alignbytes=4, prototype=define
  Linker and Libraries:
    ld='gcc'
l', ldflags =' -L/usr/local/lib'
ldflags_use'
    libpth=/usr/local/lib /lib /usr/lib
    libs=-lnsl -lgdbm -ldb -ldl -lm -lpthread -lc -lcrypt -lutil
    perllibs=
    libc=/lib/libc-2.3.2.so, so=so, useshrplib=true, libperl=libper
    gnulibc_version='2.3.2'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so', d_dlsymun=undef,
ccdlflags='-rdynamic
-Wl,-rpath,/usr/lib/perl5/5.8.0/i386-linux-thread-multi/CORE'
    cccdlflags='-fPIC'
ccdlflags='-rdynamic -Wl,-rpath,/usr/lib/perl5', lddlflags='s
Unicode/Normalize XS/A'


Characteristics of this binary (from libperl):
  Compile-time options: DEBUGGING MULTIPLICITY USE_ITHREADS
USE_LARGE_FILES PERL_IMPLICIT_CONTEXT
  Locally applied patches:
        MAINT18379
  Built under linux
  Compiled at Sep 15 2003 10:03:52
  @INC:
    /usr/lib/perl5/5.8.0/i386-linux-thread-multi
    /usr/lib/perl5/5.8.0
    /usr/lib/perl5/site_perl/5.8.0/i386-linux-thread-multi
    /usr/lib/perl5/site_perl/5.8.0
    /usr/lib/perl5/site_perl
    /usr/lib/perl5/vendor_perl/5.8.0/i386-linux-thread-multi
    /usr/lib/perl5/vendor_perl/5.8.0
    /usr/lib/perl5/vendor_perl
    /usr/lib/perl5/5.8.0/i386-linux-thread-multi
    /usr/lib/perl5/5.8.0
    .

This problem should be fixed with the current perl-5.8.0-89.10 release in 
RHEL-3-U6, as it backported code from perl-5.8.3+. Closing as CURRENTRELEASE.
If this bug is still a problem for you on RHEL-3-U6, please re-open this bug.