Allow warnings from the settings service to expire

* Setting service warning expiration

* use a hash to reduces writes in the state file

* Add documentation

* Change the code to appease t/01-settings.t

Author: blogh

check_pgactivity

@@ -7670,23 +7670,33 @@ again with the argument C<--save>.
 
 No perfdata.
 
-Critical and Warning thresholds are ignored.
+The Critical thresholds is ignored.
 
-A Critical is raised if at least one parameter changed.
+Warning is raised when the time since configuration change is less than the
+warning threshold. Obviously these alerts will disappear from themselves
+once enough time has passed. This doesn't apply for configuration changes with
+pending restart warnings.
 
 Required privileges: unprivileged role.
 
 =cut
 
 sub check_settings {
     my $me  = 'POSTGRES_SETTINGS';
+    my $this_msg;
+    my $now = gettimeofday();
+    my $expected_result = 0; # Ok
     my @long_msg;
     my @hosts;
     my @rs;
     my %settings;
+    my %settings_laste;
+    my $settings_lastemsg;
+    my $settings_lastedate;
     my %new_settings;
     my $pending_count = 0;
     my %args  = %{ $_[0] };
+    my $w_limit;
     my %queries = (
         $PG_VERSION_90 => q{
         SELECT coalesce(r.rolname, '*'), coalesce(d.datname, '*'),
@@ -7713,12 +7723,14 @@ sub check_settings {
     );
 
     @hosts = @{ parse_hosts %args };
+    $w_limit = get_time $args{'warning'}  if (defined $args{'warning'});
 
     is_compat $hosts[0], 'settings', $PG_VERSION_90 or exit 1;
 
     @rs = @{ query_ver( $hosts[0], %queries ) };
 
     %settings = %{ load( $hosts[0], 'settings', $args{'status-file'} ) || {} };
+    %settings_laste = %{ load( $hosts[0], 'settings_laste', $args{'status-file'} ) || {} };
 
     # Save settings on the very first call
     $args{'save'} = 1 unless %settings;
@@ -7756,16 +7768,37 @@ PARAM_LOOP: foreach my $row (@rs) {
         }
     }
 
+    $expected_result = 2 if scalar @long_msg;   # Regular warning
+    $expected_result = 1 if $pending_count > 0; # Pending restart
+    $this_msg = join('\0', @long_msg);
+    $settings_lastemsg = $settings_laste{'msg'} // "";
+    $settings_lastedate = $settings_laste{'date'} // $now;
+
+    if ( $this_msg ne $settings_lastemsg ) {
+        $settings_laste{'msg'} = $this_msg;
+        $settings_laste{'date'} = $now;
+        save $hosts[0], 'settings_laste', \%settings_laste, $args{'status-file'};
+    } else {
+        my $duration = $now - $settings_lastedate;
+
+        if ( defined $w_limit && $expected_result eq 2 && $duration >= $w_limit ) {
+            # Should have been a warning but the warning treshold has expired.
+            # Pending restart changes are not subject to this expiration.
+            $expected_result = 0;
+            $args{'save'} = 1;
+        }
+    }
+
     if ( $args{'save'} ) {
         save $hosts[0], 'settings', \%new_settings, $args{'status-file'};
         return status_ok( $me, [ "Setting saved" ] )
     }
 
     return status_warning( $me, [ 'Setting changed and pending restart!' ], undef, \@long_msg )
-        if $pending_count > 0;
+        if $expected_result == 1;
 
     return status_warning( $me, [ 'Setting changed!' ], undef, \@long_msg )
-        if scalar @long_msg;
+        if $expected_result == 2;
 
     return status_ok( $me, [ "Setting OK" ] );
 }
@@ -9763,7 +9796,7 @@ pod2usage(
 pod2usage(
     -message => 'FATAL: you must provide both warning and critical thresholds.',
     -exitval => 127
-) if $args{'service'} !~ m/^(pga_version|minor_version|uptime)$/ and (
+) if $args{'service'} !~ m/^(pga_version|minor_version|uptime|settings)$/ and (
     ( defined $args{'critical'} and not defined $args{'warning'} )
     or ( not defined $args{'critical'} and defined $args{'warning'} ));