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# This program is copyright 2009-2011 Percona Inc.
# Feedback and improvements are welcome.
#
# THIS PROGRAM IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR IMPLIED
# WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
# MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
#
# This program is free software; you can redistribute it and/or modify it under
# the terms of the GNU General Public License as published by the Free Software
# Foundation, version 2; OR the Perl Artistic License. On UNIX and similar
# systems, you can issue `man perlgpl' or `man perlartistic' to read these
# licenses.
#
# You should have received a copy of the GNU General Public License along with
# this program; if not, write to the Free Software Foundation, Inc., 59 Temple
# Place, Suite 330, Boston, MA 02111-1307 USA.
# ###########################################################################
# ExecutionThrottler package
# ###########################################################################
{
# Package: ExecutionThrottler
# ExecutionThrottle slows program execution if a threshold is exceeded.
package ExecutionThrottler;
use strict;
use warnings FATAL => 'all';
use English qw(-no_match_vars);
use constant PTDEBUG => $ENV{PTDEBUG} || 0;
use List::Util qw(sum min max);
use Time::HiRes qw(time);
use Data::Dumper;
$Data::Dumper::Indent = 1;
$Data::Dumper::Sortkeys = 1;
$Data::Dumper::Quotekeys = 0;
# Arguments:
# * rate_max scalar: maximum allowable execution rate
# * get_rate subref: callback to get the current execution rate
# * check_int scalar: check interval in seconds for calling get_rate()
# * step scalar: incr/decr skip_prob in step increments
sub new {
my ( $class, %args ) = @_;
my @required_args = qw(rate_max get_rate check_int step);
foreach my $arg ( @required_args ) {
die "I need a $arg argument" unless defined $args{$arg};
}
my $self = {
step => 0.05, # default
%args,
rate_ok => undef,
last_check => undef,
stats => {
rate_avg => 0,
rate_samples => [],
},
int_rates => [],
skip_prob => 0.0,
};
return bless $self, $class;
}
sub throttle {
my ( $self, %args ) = @_;
my $time = $args{misc}->{time} || time;
if ( $self->_time_to_check($time) ) {
my $rate_avg = (sum(@{$self->{int_rates}}) || 0)
/ (scalar @{$self->{int_rates}} || 1);
my $running_avg = $self->_save_rate_avg($rate_avg);
PTDEBUG && _d('Average rate for last interval:', $rate_avg);
if ( $args{stats} ) {
$args{stats}->{throttle_checked_rate}++;
$args{stats}->{throttle_rate_avg} = sprintf '%.2f', $running_avg;
}
@{$self->{int_rates}} = ();
if ( $rate_avg > $self->{rate_max} ) {
# Rates is too high; increase the probability that the event
# will be skipped.
$self->{skip_prob} += $self->{step};
$self->{skip_prob} = 1.0 if $self->{skip_prob} > 1.0;
PTDEBUG && _d('Rate max exceeded');
$args{stats}->{throttle_rate_max_exceeded}++ if $args{stats};
}
else {
# The rate is ok; decrease the probability that the event
# will be skipped.
$self->{skip_prob} -= $self->{step};
$self->{skip_prob} = 0.0 if $self->{skip_prob} < 0.0;
$args{stats}->{throttle_rate_ok}++ if $args{stats};
}
PTDEBUG && _d('Skip probability:', $self->{skip_prob});
$self->{last_check} = $time;
}
else {
my $current_rate = $self->{get_rate}->();
push @{$self->{int_rates}}, $current_rate;
if ( $args{stats} ) {
$args{stats}->{throttle_rate_min} = min(
($args{stats}->{throttle_rate_min} || ()), $current_rate);
$args{stats}->{throttle_rate_max} = max(
($args{stats}->{throttle_rate_max} || ()), $current_rate);
}
PTDEBUG && _d('Current rate:', $current_rate);
}
# rand() returns a fractional value between [0,1). If skip_prob is
# 0 then, then no queries will be skipped. If its 1.0, then all queries
# will be skipped. skip_prop is adjusted above; it depends on the
# average rate.
if ( $args{event} ) {
$args{event}->{Skip_exec} = $self->{skip_prob} <= rand() ? 'No' : 'Yes';
}
return $args{event};
}
sub _time_to_check {
my ( $self, $time ) = @_;
if ( !$self->{last_check} ) {
$self->{last_check} = $time;
return 0;
}
return $time - $self->{last_check} >= $self->{check_int} ? 1 : 0;
}
sub rate_avg {
my ( $self ) = @_;
return $self->{stats}->{rate_avg} || 0;
}
sub skip_probability {
my ( $self ) = @_;
return $self->{skip_prob};
}
sub _save_rate_avg {
my ( $self, $rate ) = @_;
my $samples = $self->{stats}->{rate_samples};
push @$samples, $rate;
shift @$samples if @$samples > 1_000;
$self->{stats}->{rate_avg} = sum(@$samples) / (scalar @$samples);
return $self->{stats}->{rate_avg} || 0;
}
sub _d {
my ($package, undef, $line) = caller 0;
@_ = map { (my $temp = $_) =~ s/\n/\n# /g; $temp; }
map { defined $_ ? $_ : 'undef' }
@_;
print STDERR "# $package:$line $PID ", join(' ', @_), "\n";
}
1;
}
# ###########################################################################
# End ExecutionThrottler package
# ###########################################################################
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