[PATCH] pop3: speed up STAT slightly (~1%)

[Eric Wong <e@80x24.org>]

We can calculate the total size of the mailbox while generating
the cache, which allows us to iterate the cache again to
calculate the size of the mailbox slice.  While we're in the
area, simplify the loop and avoid needlessly updating the `$beg'
variable.

This adds a small amount of constant time overhead to DELE,
however that is amortized across multiple requests for fairness.
---
 lib/PublicInbox/POP3.pm | 25 +++++++++++++------------
 1 file changed, 13 insertions(+), 12 deletions(-)

diff --git a/lib/PublicInbox/POP3.pm b/lib/PublicInbox/POP3.pm
index 19fcc434..5f992e14 100644
--- a/lib/PublicInbox/POP3.pm
+++ b/lib/PublicInbox/POP3.pm
@@ -149,32 +149,32 @@ SELECT num,ddd FROM over WHERE num >= ? AND num <= ?
 ORDER BY num ASC
 
 	$sth->execute($beg, $end);
-	do {
-		$m = $sth->fetchall_arrayref({}, 1000);
+	my $tot = 0;
+	while (defined($m = $sth->fetchall_arrayref({}, 1000))) {
 		for my $x (@$m) {
 			PublicInbox::Over::load_from_row($x);
 			push(@cache, $x->{num}, $x->{bytes} + 0, $x->{blob});
 			undef $x; # saves ~1.5M memory w/ 50k messages
+			$tot += $cache[-2];
 		}
-	} while (scalar(@$m) && ($beg = $cache[-3] + 1));
-	\@cache;
+	}
+	$self->{total_bytes} = $tot;
+	$self->{cache} = \@cache;
 }
 
 sub cmd_stat {
 	my ($self) = @_;
 	my $err; $err = need_txn($self) and return $err;
-	my $cache = $self->{cache} //= _stat_cache($self);
-	my $tot = 0;
-	for (my $i = 1; $i < scalar(@$cache); $i += 3) { $tot += $cache->[$i] }
+	my $cache = $self->{cache} // _stat_cache($self);
 	my $nr = @$cache / 3 - ($self->{nr_dele} // 0);
-	"+OK $nr $tot\r\n";
+	"+OK $nr $self->{total_bytes}\r\n";
 }
 
 # for LIST and UIDL
 sub _list {
 	my ($desc, $idx, $self, $msn) = @_;
 	my $err; $err = need_txn($self) and return $err;
-	my $cache = $self->{cache} //= _stat_cache($self);
+	my $cache = $self->{cache} // _stat_cache($self);
 	if (defined $msn) {
 		my $base_off = ($msn - 1) * 3;
 		my $val = $cache->[$base_off + $idx] //
@@ -204,8 +204,9 @@ sub mark_dele ($$) {
 	my $old = $self->{txn_max_uid} //= $uid;
 	$self->{txn_max_uid} = $uid if $uid > $old;
 
+	$self->{total_bytes} -= $cache->[$base_off + 1];
 	$cache->[$base_off] = undef; # clobber UID
-	$cache->[$base_off + 1] = 0; # zero bytes (simplifies cmd_stat)
+	$cache->[$base_off + 1] = undef; # clobber bytes
 	$cache->[$base_off + 2] = undef; # clobber oidhex
 	++$self->{nr_dele};
 }
@@ -247,7 +248,7 @@ sub cmd_retr {
 	return \"-ERR lines must be a non-negative number\r\n" if
 			(defined($top_nr) && $top_nr !~ /\A[0-9]+\z/);
 	my $err; $err = need_txn($self) and return $err;
-	my $cache = $self->{cache} //= _stat_cache($self);
+	my $cache = $self->{cache} // _stat_cache($self);
 	my $off = $msn - 1;
 	my $hex = $cache->[$off * 3 + 2] // return \"-ERR no such message\r\n";
 	${ibx_async_cat($self->{ibx}, $hex, \&retr_cb,
@@ -267,7 +268,7 @@ sub cmd_rset {
 sub cmd_dele {
 	my ($self, $msn) = @_;
 	my $err; $err = need_txn($self) and return $err;
-	$self->{cache} //= _stat_cache($self);
+	$self->{cache} // _stat_cache($self);
 	$msn =~ /\A[1-9][0-9]*\z/ or return \"-ERR no such message\r\n";
 	mark_dele($self, $msn - 1) ? \"+OK\r\n" : \"-ERR no such message\r\n";
 }