DBI/mysql gathering all rows on execute

sgifford has asked for the wisdom of the Perl Monks concerning the following question:

I'm doing a query that returns many rows, using DBI and DBD::mysql. I expect the $sth->execute to get the query started and return almost immediately, and then one of the fetchrow methods to actually get the results. Instead, execute seems to gather all of the results before returning, taking a long time to finish and using up over 1GB of memory.

Is there a way to work around this?

Here's my code. It gets to "Executing..." and then sits there for a very long time taking up memory; based on other tests it will eventually return, and after that the fetchrows will work.

#!/usr/bin/perl -w

BEGIN {
  $ENV{MYSQL_UNIX_PORT}='/clair8/corpora/aledb/run/socket';
};

use strict;
use DBI;

my $sql = "SELECT url1.urlid AS from_id, url1.url AS from_url, link1.l
+ink_text AS link1_text, link1.linkid AS link1_id, url2.urlid AS to_id
+, url2.url AS to_url
FROM  DOTGOV_links AS link1, DOTGOV_urls AS url1, DOTGOV_urls AS url2
        WHERE (link1.link_from = url1.urlid) 
          AND (link1.link_to = url2.urlid)";


warn "Connecting...\n";
my $dbh = DBI->connect('DBI:mysql:database=clair', 'root','', {AutoCom
+mit => 1})
    or die "Error creating dbh.\n";
warn "Connected!\n";

warn "Preparing...\n";
my $sth = $dbh->prepare($sql)
    or die "Error preparing sth.\n";
warn "Prepared!\n";

warn "Executing...\n";
$sth->execute
    or die "Error executing sth.\n";
warn "Executed!\n";

warn "Finishing...\n";
$sth->finish
    or die "Error finishing sth.\n";
warn "Finished!\n";
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