Since open/close is too slow, perhaps you might try a database, like sqlite?

I made a small test program and the output seems to indicate that it would be significantly faster:

C:\> perl trymany.pl
connecting to dbi:SQLite:db.sqlite3 ...
connected to dbi:SQLite:db.sqlite3
ready to begin
              Rate openclose    sqlite
openclose   2580/s        --      -98%
sqlite    121065/s     4593%        --
[download]

The code is:

#!/usr/bin/perl
# trymany - compare open/write/close with db access
#vim: syntax=perl

use v5.14;
use warnings;

use Benchmark qw( :all );
use File::Path qw( make_path );
use DBI;

sub make_file_name { #FUNCTION $top -> $name
        my ($top) = @_;
        my $f = $top . '/' . sprintf "%04d", rand(10000);
        return $f;
}
sub make_dir { #FUNCTION $dir -> $dir
        my ($dir) = @_;
        return $dir if (-d $dir);
        my $ok = make_path($dir) or die "cannot mkdir $dir: $!\n";
        return $dir;
}

my $db_file = "db.sqlite3";
my $dsn = "dbi:SQLite:$db_file";
my $table = "testtab";
my $column = "data";
my $insert_sql = "insert into $table ($column) values (?)";
my $create_sql = "create table $table ($column varchar)";
my $commit_every = 1000;
my $uncommitted = 0;
my $record = 'x' x 80;
my $create_table = (-f $db_file) ? 0 : 1;
my $top = "dirs";

make_dir($top) or die "cannot mkdir $top $!\n";
my $n = (shift @ARGV) || 100000;
my $seed = (shift @ARGV) || 12523477;
srand($seed);

warn "connecting to $dsn ...\n";
my $dbh = DBI->connect($dsn, '', '', {
        AutoCommit      => 0,
        PrintError      => 1,
        RaiseError      => 1,
}) or die "cannot connect to $dsn: $!\n";
warn "connected to $dsn\n";

if ($create_table) {
        $dbh->do($create_sql) or die "cannot create table $DBI::errstr
+\n";
        warn "created table\n";
}

my $sth = $dbh->prepare($insert_sql) or die "cannot prepare: $DBI::err
+str\n";
my $first_sqlite = 1;
warn "ready to begin\n";

cmpthese( $n, {
        openclose       => sub {
                state $dir = make_dir("$top/openclose");
                my $f = make_file_name($dir);
                open my $fh, ">>$f" or die "cannot open $f for append;
+ $!\n";
                defined(print $fh $record) or die "cannot write $f: $!
+\n";;
                close($fh) or die "cannot close $f: $!\n";
        },
        sqlite          => sub {
                $sth->execute($record) or die "cannot insert: $DBI::er
+rstr\n";
                ++$uncommitted;
                if ($uncommitted >= $commit_every) {
                        $dbh->commit or die "cannot commit $DBI::errst
+r\n";
                        $uncommitted = 0;
                }
        },
});
[download]