Add to GitwebCache::SimpleFileCache support for adaptive lifetime
(cache expiration) control. Cache lifetime can be increased or
decreased by any factor, e.g. load average, through the definition
of the 'check_load' callback.
Note that using ->set_expires_in, or unsetting 'check_load' via
->set_check_load(undef) turns off adaptive caching.
Make gitweb automatically adjust cache lifetime by load, using
get_loadavg() function. Define and describe default parameters for
dynamic (adaptive) cache expiration time control.
There are some very basic tests of dynamic expiration time in t9503,
namely checking if dynamic expire time is within given upper and lower
bounds.
Inspired-by-code-by: John 'Warthog9' Hawley <warthog9@xxxxxxxxxx>
Signed-off-by: Jakub Narebski <jnareb@xxxxxxxxx>
---
Differences from relevant parts of J.H. patch:
* 'increase_factor' is configurable rather than hardcoded 60.
* 'check_load' is passed via conctructor parameter; gitweb by default
sets it to \&get_loadavg. This means that the caching engine is not
entangled with gitweb (and for example can be tested separately).
gitweb/gitweb.perl | 25 ++++++++-
gitweb/lib/GitwebCache/SimpleFileCache.pm | 79 +++++++++++++++++++++++++++--
t/t9503/test_cache_interface.pl | 33 ++++++++++++
3 files changed, 130 insertions(+), 7 deletions(-)
diff --git a/gitweb/gitweb.perl b/gitweb/gitweb.perl
index 4322b28..12e04a1 100755
--- a/gitweb/gitweb.perl
+++ b/gitweb/gitweb.perl
@@ -304,8 +304,29 @@ our %cache_options = (
# (00-ff). Must be larger than 0.
'cache_depth' => 1,
- # The (global) expiration time for objects placed in the cache, in seconds.
- 'expires_in' => 20,
+ # The (global) minimum expiration time for objects placed in the cache,
+ # in seconds. If the dynamic adaptive cache exporation time is lower
+ # than this number, we set cache timeout to this minimum.
+ 'expires_min' => 20, # 20 seconds
+
+ # The (global) maximum expiration time for dynamic (adaptive) caching
+ # algorithm, in seconds. If the adaptive cache lifetime exceeds this
+ # number, we set cache timeout to this maximum.
+ # (If 'expires_min' >= 'expires_max', there is no adaptive cache timeout,
+ # and 'expires_min' is used as expiration time for objects in cache.)
+ 'expires_max' => 1200, # 20 minutes
+
+ # Cache lifetime will be increased by applying this factor to the result
+ # from 'check_load' callback (see below).
+ 'expires_factor' => 60, # expire time in seconds for 1.0 (100% CPU) load
+
+ # User supplied callback for deciding the cache policy, usually system
+ # load. Multiplied by 'expires_factor' gives adaptive expiration time,
+ # in seconds, subject to the limits imposed by 'expires_min' and
+ # 'expires_max' bounds. Set to undef (or delete) to turn off dynamic
+ # lifetime control.
+ # (Compatibile with Cache::Adaptive.)
+ 'check_load' => \&get_loadavg,
);
# Set to _initialized_ instance of GitwebCache::Capture compatibile capturing
# engine, i.e. one implementing ->new() constructor, and ->capture($code)
diff --git a/gitweb/lib/GitwebCache/SimpleFileCache.pm b/gitweb/lib/GitwebCache/SimpleFileCache.pm
index bf74f7c..581a574 100644
--- a/gitweb/lib/GitwebCache/SimpleFileCache.pm
+++ b/gitweb/lib/GitwebCache/SimpleFileCache.pm
@@ -61,6 +61,22 @@ our $DEFAULT_NAMESPACE = '';
# 'expires_in' (CHI compatibile) [seconds]
# The expiration time for objects place in the cache.
# Defaults to -1 (never expire) if not explicitly set.
+# Sets 'expires_min' to given value.
+# * 'expires_min' [seconds]
+# The minimum expiration time for objects in cache (e.g. with 0% CPU load).
+# Used as lower bound in adaptive cache lifetime / expiration.
+# Defaults to 20 seconds; 'expires_in' sets it also.
+# * 'expires_max' [seconds]
+# The maximum expiration time for objects in cache.
+# Used as upper bound in adaptive cache lifetime / expiration.
+# Defaults to 1200 seconds, if not set;
+# defaults to 'expires_min' if 'expires_in' is used.
+# * 'check_load'
+# Subroutine (code) used for adaptive cache lifetime / expiration.
+# If unset, adaptive caching is turned off; defaults to unset.
+# * 'increase_factor' [seconds / 100% CPU load]
+# Factor multiplying 'check_load' result when calculating cache lietime.
+# Defaults to 60 seconds for 100% SPU load ('check_load' returning 1.0).
sub new {
my $class = shift;
my %opts = ref $_[0] ? %{ $_[0] } : @_;
@@ -68,7 +84,8 @@ sub new {
my $self = {};
$self = bless($self, $class);
- my ($root, $depth, $ns, $expires_in);
+ my ($root, $depth, $ns);
+ my ($expires_min, $expires_max, $increase_factor, $check_load);
if (%opts) {
$root =
$opts{'cache_root'} ||
@@ -77,19 +94,31 @@ sub new {
$opts{'cache_depth'} ||
$opts{'depth'};
$ns = $opts{'namespace'};
- $expires_in =
+ $expires_min =
+ $opts{'expires_min'} ||
$opts{'default_expires_in'} ||
$opts{'expires_in'};
+ $expires_max =
+ $opts{'expires_max'};
+ $increase_factor = $opts{'expires_factor'};
+ $check_load = $opts{'check_load'};
}
$root = $DEFAULT_CACHE_ROOT unless defined($root);
$depth = $DEFAULT_CACHE_DEPTH unless defined($depth);
$ns = $DEFAULT_NAMESPACE unless defined($ns);
- $expires_in = -1 unless defined($expires_in); # <0 means never
+ $expires_min = -1 unless defined($expires_min);
+ $expires_max = $expires_min
+ if (!defined($expires_max) && exists $opts{'expires_in'});
+ $expires_max = -1 unless (defined($expires_max));
+ $increase_factor = 60 unless defined($increase_factor);
$self->set_root($root);
$self->set_depth($depth);
$self->set_namespace($ns);
- $self->set_expires_in($expires_in);
+ $self->set_expires_min($expires_min);
+ $self->set_expires_max($expires_max);
+ $self->set_increase_factor($increase_factor);
+ $self->set_check_load($check_load);
return $self;
}
@@ -101,7 +130,8 @@ sub new {
# http://perldesignpatterns.com/perldesignpatterns.html#AccessorPattern
# creates get_depth() and set_depth($depth) etc. methods
-foreach my $i (qw(depth root namespace expires_in)) {
+foreach my $i (qw(depth root namespace
+ expires_min expires_max increase_factor check_load)) {
my $field = $i;
no strict 'refs';
*{"get_$field"} = sub {
@@ -114,6 +144,45 @@ foreach my $i (qw(depth root namespace expires_in)) {
};
}
+# ......................................................................
+# pseudo-accessors
+
+# returns adaptive lifetime of cache entry for given $key [seconds]
+sub get_expires_in {
+ my ($self) = @_;
+
+ # short-circuit
+ if (!defined $self->{'check_load'} ||
+ $self->{'expires_max'} <= $self->{'expires_min'}) {
+ return $self->{'expires_min'};
+ }
+
+ my $expires_in =
+ #$self->{'expires_min'} +
+ $self->{'increase_factor'} * $self->check_load();
+
+ if ($expires_in < $self->{'expires_min'}) {
+ return $self->{'expires_min'};
+ } elsif ($expires_in > $self->{'expires_max'}) {
+ return $self->{'expires_max'};
+ }
+
+ return $expires_in;
+}
+
+# sets expiration time to $duration, turns off adaptive cache lifetime
+sub set_expires_in {
+ my ($self, $duration) = @_;
+
+ $self->{'expires_min'} = $self->{'expires_max'} = $duration;
+}
+
+# runs 'check_load' subroutine, for adaptive cache lifetime.
+# Note: check in caller that 'check_load' exists.
+sub check_load {
+ my $self = shift;
+ return $self->{'check_load'}->();
+}
# ----------------------------------------------------------------------
# utility functions and methods
diff --git a/t/t9503/test_cache_interface.pl b/t/t9503/test_cache_interface.pl
index 1517fb6..9513043 100755
--- a/t/t9503/test_cache_interface.pl
+++ b/t/t9503/test_cache_interface.pl
@@ -101,4 +101,37 @@ subtest 'cache expiration' => sub {
done_testing();
};
+# Test assertions for adaptive cache expiration
+#
+my $load = 0.0;
+sub load { return $load; }
+my $expires_min = 10;
+my $expires_max = 30;
+$cache->set_expires_in(-1);
+$cache->set_expires_min($expires_min);
+$cache->set_expires_max($expires_max);
+$cache->set_check_load(\&load);
+subtest 'adaptive cache expiration' => sub {
+ cmp_ok($cache->get_expires_min(), '==', $expires_min,
+ '"expires min" set correctly');
+ cmp_ok($cache->get_expires_max(), '==', $expires_max,
+ '"expires max" set correctly');
+
+ $load = 0.0;
+ cmp_ok($cache->get_expires_in(), '>=', $expires_min,
+ '"expires in" bound from down for load=0');
+ cmp_ok($cache->get_expires_in(), '<=', $expires_max,
+ '"expires in" bound from up for load=0');
+
+ $load = 1_000;
+ cmp_ok($cache->get_expires_in(), '>=', $expires_min,
+ '"expires in" bound from down for heavy load');
+ cmp_ok($cache->get_expires_in(), '<=', $expires_max,
+ '"expires in" bound from up for heavy load');
+
+ done_testing();
+};
+
+$cache->set_expires_in(-1);
+
done_testing();
--
1.7.3
--
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