Simplify ReplicaLagLimiter::update().

lib/ReplicaLagLimiter.pm

@@ -23,11 +23,9 @@
 # There are two sides to this problem: operations on the master and
 # slave lag.  Master ops that replicate can affect slave lag, so they
 # should be adjusted to prevent overloading slaves.  <update()> returns
-# and adjustment (-1=down/decrease, 0=none, 1=up/increase) based on
-# an weighted decaying average of how long operations are taking on the
-# master.  The desired master op time range is specified by target_time.
-# By default, the running avg is weight is 0.75; or, new times weight
-# only 0.25 so temporary variations won't cause volatility.
+# an adjusted "n" value (number of whatever the master is doing) based
+# on a weighted decaying average of "t", how long operations are taking.
+# The desired master op time range is specified by target_t.
 #
 # Regardless of all that, slaves may still lag, so <wait()> waits for them
 # to catch up based on the spec passed to <new()>.
@@ -46,17 +44,18 @@ use Time::HiRes qw(sleep time);
 #   spec      - --replicat-lag spec (arrayref of option=value pairs)
 #   slaves    - Arrayref of slave cxn, like [{dsn=>{...}, dbh=>...},...]
 #   get_lag   - Callback passed slave dbh and returns slave's lag
-#   target_time - Target time for master ops
+#   initial_n - Initial n value for <update()>
+#   initial_t - Initial t value for <update()>
+#   target_t  - Target time for t in <update()>
 #
 # Optional Arguments:
-#   sample_size - Number of master op samples to use for moving avg (default 5)
-#   weight      - Weight of previous average (default 0.75).
+#   weight - Weight of previous n/t values (default 0.75).
 #
 # Returns:
 #   ReplicaLagLimiter object 
 sub new {
    my ( $class, %args ) = @_;
-   my @required_args = qw(spec slaves get_lag target_time);
+   my @required_args = qw(spec slaves get_lag initial_n initial_t target_t);
    foreach my $arg ( @required_args ) {
       die "I need a $arg argument" unless $args{$arg};
    }
@@ -74,12 +73,11 @@ sub new {
       check     => 1,     # sleep time between checking slave lag
       continue  => 'no',  # return true even if timeout
       %specs,             # slave wait specs from caller
-      samples     => [],    # master op times
-      moving_avg  => 0,     # moving avgerge of samples
       slaves    => $args{slaves},
       get_lag   => $args{get_lag},
-      target_time => $args{target_time},
-      sample_size => $args{sample_size} || 5,
+      avg_n     => $args{initial_n},
+      avg_t     => $args{initial_t},
+      target_t  => $args{target_t},
       weight    => $args{weight} || 0.75,
    };
 
@@ -123,44 +121,22 @@ sub validate_spec {
 #
 # Parameters:
 #   n - Number of operations (rows, etc.)
-#   s - Amount of time in seconds that n took
+#   t - Amount of time in seconds that n took
 #
 # Returns:
-#   -1 master op is too slow, it should be reduced
-#    0 master op is within target time range, no adjustment
-#    1 master is too fast; it can be increased 
+#   n adjust to meet target_t based on weighted decaying avg rate
 sub update {
-   my ($self, $n, $s) = @_;
-   MKDEBUG && _d('Master op time:', $n, 'n /', $s, 's');
-   my $adjust = 0;
-   if ( $self->{avg_rate} ) { 
-      # Calculated new weighted averages.
-      $self->{avg_n}    = ($self->{avg_n} * (    $self->{weight}))
-                        + ($n             * (1 - $self->{weight}));
-      $self->{avg_s}    = ($self->{avg_s} * (    $self->{weight}))
-                        + ($s             * (1 - $self->{weight}));
-      $self->{avg_rate} = int($self->{avg_n} / $self->{avg_s});
-      MKDEBUG && _d('Weighted avg n:', $self->{avg_n}, 's:', $self->{avg_s},
-         'rate:', $self->{avg_rate}, 'n/s');
+   my ($self, $n, $t) = @_;
+   MKDEBUG && _d('Master op time:', $n, 'n /', $t, 's');
 
-      $adjust = $self->{avg_s} < $self->{target_time} ?  1
-              : $self->{avg_s} > $self->{target_time} ? -1
-              :                                          0;
-   }
-   else {
-      MKDEBUG && _d('Saved values; initializing averages');
-      $self->{n_vals}++;
-      $self->{total_n} += $n;
-      $self->{total_s} += $s;
-      if ( $self->{n_vals} == $self->{sample_size} ) {
-         $self->{avg_n}    = $self->{total_n} / $self->{n_vals};
-         $self->{avg_s}    = $self->{total_s} / $self->{n_vals};
-         $self->{avg_rate} = int($self->{avg_n}   / $self->{avg_s});
-         MKDEBUG && _d('Initial avg n:', $self->{avg_n}, 's:', $self->{avg_s},
-            'rate:', $self->{avg_rate}, 'n/s');
-      }
-   }
-   return $adjust;
+   $self->{avg_n}    = ($self->{avg_n} * $self->{weight}) + $n;
+   $self->{avg_t}    = ($self->{avg_t} * $self->{weight}) + $t;
+   $self->{avg_rate} = $self->{avg_n}  / $self->{avg_t};
+   MKDEBUG && _d('Weighted avg rate:', $self->{avg_rate}, 'n/s');
+
+   my $new_n = int($self->{avg_rate} * $self->{target_t});
+   MKDEBUG && _d('Adjust n to', $new_n);
+   return $new_n;
 }
 
 # Sub: wait_for_slave

t/lib/ReplicaLagLimiter.t

@@ -9,7 +9,7 @@ BEGIN {
 use strict;
 use warnings FATAL => 'all';
 use English qw(-no_match_vars);
-use Test::More tests => 16;
+use Test::More tests => 17;
 
 use ReplicaLagLimiter;
 use PerconaTest;
@@ -21,7 +21,9 @@ my $rll = new ReplicaLagLimiter(
       { dsn=>{n=>'slave2'}, dbh=>2 },
    ],
    get_lag     => \&get_lag,
-   target_time => 1,
+   initial_n   => 1000,
+   initial_t   => 1,
+   target_t    => 1,
 );
 
 # ############################################################################
@@ -68,41 +70,53 @@ throws_ok(
 # ############################################################################
 # Update master op, see if we get correct adjustment result.
 # ############################################################################
-for (1..4) {
+
+# stay the same
+for (1..5) {
    $rll->update(1000, 1);
 }
 is(
    $rll->update(1000, 1),
-   0,
-   "5 time samples, no adjustmenet"
+   1000,
+   "Same rate, same n"
 );
 
-for (1..4) {
-   $rll->update(1000, 1);
+# slow down
+for (1..5) {
+   $rll->update(1000, 2);
 }
-is(
-   $rll->update(1000, 1),
-   0,
-   "Avg hasn't changed"
-);
-
-# Results in: Weighted avg n: 1000 s: 1.683593 rate: 593 n/s
-$rll->update(1000, 2);
-$rll->update(1000, 2);
-$rll->update(1000, 2);
 is(
    $rll->update(1000, 2),
-   -1,
-   "Adjust down"
+   542,
+   "Decrease rate, decrease n"
 );
 
-# Results in: Weighted avg n: 1000 s: 0.768078 rate: 1301 n/s
-$rll->update(1000, 0.1);
-$rll->update(1000, 0.1);
+for (1..15) {
+   $rll->update(1000, 2);
+}
 is(
-   $rll->update(1000, 0.1),
-   1,
-   "Adjust up"
+   $rll->update(1000, 2),
+   500,
+   "limit n=500 decreasing"
+);
+
+# speed up
+for (1..5) {
+   $rll->update(1000, 1);
+}
+is(
+   $rll->update(1000, 1),
+   849,
+   "Increase rate, increase n"
+);
+
+for (1..20) {
+   $rll->update(1000, 1);
+}
+is(
+   $rll->update(1000, 1),
+   999,
+   "limit n=1000 increasing"
 );
 
 # ############################################################################
@@ -153,7 +167,9 @@ $rll = new ReplicaLagLimiter(
       { dsn=>{n=>'slave2'}, dbh=>2 },
    ],
    get_lag     => \&get_lag,
-   target_time => [0.9,1.1],
+   initial_n   => 1000,
+   initial_t   => 1,
+   target_t    => 1,
 );
 
 @waited = ();
@@ -172,7 +188,9 @@ $rll = new ReplicaLagLimiter(
       { dsn=>{n=>'slave2'}, dbh=>2 },
    ],
    get_lag     => \&get_lag,
-   target_time => [0.9,1.1],
+   initial_n   => 1000,
+   initial_t   => 1,
+   target_t    => 1,
 );
 
 @waited = ();