We no longer assume a normal distribution of latencies but instead use

percentiles when calculating a life probability of an outstanding ping.  Also
we do not show the mean of latency but the median as this seems to be 'more
correct'.
This also means we no longer need the normal distribution libraries from lib/

1 files changed, 52 insertions, 37 deletions

diff --git a/Echolot/Stats.pm b/Echolot/Stats.pm
index 905f210..c7255c7 100644
--- a/Echolot/Stats.pm
+++ b/Echolot/Stats.pm
@@ -1,7 +1,7 @@
 package Echolot::Stats;
 
 # (c) 2002 Peter Palfrader <peter@palfrader.org>
-# $Id: Stats.pm,v 1.56 2003/06/06 09:32:37 weasel Exp $
+# $Id: Stats.pm,v 1.57 2003/06/06 11:27:59 weasel Exp $
 #
 
 =pod
@@ -21,12 +21,6 @@ use strict;
 use English;
 use Echolot::Log;
 
-use Statistics::Distrib::Normal qw{};
-
-my $NORMAL = new Statistics::Distrib::Normal;
-$NORMAL->mu(0);
-$NORMAL->sigma(1);
-
 my $STATS_DAYS;
 my $SECONDS_PER_DAY;
 
@@ -190,11 +184,36 @@ sub build_list2_capsstr($) {
 	return $str;
 }
 
+sub median($) {
+	my ($arr) = @_;
+	my $cnt = scalar @$arr;
+	if ($cnt == 0) {
+		return undef;
+	} elsif ($cnt % 2 == 0) {
+		return ($arr->[ int(($cnt - 1 ) / 2) ] + $arr->[ int($cnt / 2) ] ) / 2;
+	} else {
+		return $arr->[ int(($cnt - 1 ) / 2) ];
+	};
+};
+
+sub percentile($$) {
+	my ($lat, $lats) = @_;
+
+	my $num = scalar @$lats;
+	my $i;
+	for (my $i=0; $i < $num; $i++) {
+		last if $lat < $lats->[$i];
+	}
+	return ($num - $i) / $num;
+}
 
 sub calculate($$) {
 	my ($addr, $types) = @_;
 	my $now = time();
 
+	my $SKEW_ABS = 15*60;
+	my $SKEW_PERCENT = 0.80;
+
 	my @out;
 	my @done;
 	
@@ -207,51 +226,47 @@ sub calculate($$) {
 		};
 	};
 
-	my $latency = 0;
-	my $received = 0;
-	my $sent = 0;
-	my @latency;
-	my @received;
-	my @sent;
+	my @latency_total = map { $_->[1] } @done;
+	my @latency_day;
+	my $sent_total;
+	my $received_total;
+	my @sent_day;
+	my @received_day;
 	for my $done (@done) {
-		$latency += $done->[1];   $latency [int(($now - $done->[0]) / $SECONDS_PER_DAY)] += $done->[1];
-		$sent ++;                 $sent    [int(($now - $done->[0]) / $SECONDS_PER_DAY)] ++;
-		$received ++;             $received[int(($now - $done->[0]) / $SECONDS_PER_DAY)] ++;
-	};
-	$latency /= (scalar @done) if (scalar @done);
-	$latency = undef unless (scalar @done);
-	for ( 0 .. $STATS_DAYS - 1 ) {
-		$latency[$_] /= $received[$_] if ($received[$_]);
+		push @{ $latency_day [int(($now - $done->[0]) / $SECONDS_PER_DAY)] }, $done->[1];
+		$sent_total ++;     $sent_day    [int(($now - $done->[0]) / $SECONDS_PER_DAY)] ++;
+		$received_total ++; $received_day[int(($now - $done->[0]) / $SECONDS_PER_DAY)] ++;
 	};
 
-	my $variance = 0;
-	$variance += ($latency - $_->[1]) ** 2 for (@done);
-	$variance /= (scalar @done) if (scalar @done);
-
-	my $deviation = sqrt($variance);
+	@latency_total = sort { $a <=> $b } @latency_total;
+	my $latency_median = median (\@latency_total);
+	my @latency_median_day;
+	for ( 0 .. $STATS_DAYS - 1 ) {
+		@{$latency_day[$_]} = sort { $a <=> $b } $latency_day[$_];
+		$latency_median_day[$_] = median ( $latency_day[$_] );
+	}
 
 	if (scalar @out) {
-		my @p = 
-			($deviation != 0) ?
-				$NORMAL->utp( map { ($now - $_ - $latency) / $deviation } @out ) :
+		my @p = ( scalar @latency_total ) ?
+				map { percentile( ($now - $_ - $SKEW_ABS)/$SKEW_PERCENT , \@latency_total ) } @out :
 				map { 0 } @out;
 		for (my $i=0; $i < scalar @out; $i++) {
-			$sent ++;            $sent    [int(($now - $out[$i]) / $SECONDS_PER_DAY)] ++;
-			$received += $p[$i]; $received[int(($now - $out[$i]) / $SECONDS_PER_DAY)] += $p[$i];
+			$sent_total ++;            $sent_day    [int(($now - $out[$i]) / $SECONDS_PER_DAY)] ++;
+			$received_total += $p[$i]; $received_day[int(($now - $out[$i]) / $SECONDS_PER_DAY)] += $p[$i];
 		};
 	};
-	$received /= $sent if ($sent);
+	$received_total /= $sent_total if ($sent_total);
 	for ( 0 .. $STATS_DAYS - 1 ) {
-		$received[$_] /= $sent[$_] if ($sent[$_]);
+		$received_day[$_] /= $sent_day[$_] if ($sent_day[$_]);
 	};
 
 
 
 	return {
-		avr_latency     => $latency,
-		avr_reliability => $received,
-		latency_day     => \@latency,
-		reliability_day => \@received
+		avr_latency     => $latency_median,
+		avr_reliability => $received_total,
+		latency_day     => \@latency_day,
+		reliability_day => \@received_day
 	};
 };