#!/usr/bin/perl -w
# Plugin for monitor postgres database cache hit miss ratio.
#
# Copyright Dalibo <cedric.villemain@dalibo.com> 2007
# Based on a plugin (postgres_block_read_) from Bjrn Ruberg <bjorn@linpro.no>
#
# Licenced under GPL v3.
#
# Usage:
#
#       Symlink into /etc/munin/plugins/ and add the monitored
#       database to the filename. e.g.:
#
#       ln -s /usr/share/munin/plugins/pg__database__blks \
#         /etc/munin/plugins/pg_databasename>_database_hitratio
#       This should, however, be given through autoconf and suggest.
#
#       If required, give username, password and/or Postgresql server
#       host through environment variables.
#
#       You must also activate Postgresql statistics. See
#       http://www.postgresql.org/docs/7.4/interactive/monitoring-stats.html
#       for how to enable this. Specifically, the following lines must
#       exist in your postgresql.conf:
#
#           stats_start_collector = true
#           stats_block_level = true
#
#
# Parameters:
#
#       config   (required)
#
# Config variables:
#
#       dbhost     - Which database server to use. Defaults to
#                    'localhost'.
#       dbname     - Which database to use. Defaults to template1
#       dbuser     - A Postgresql user account with read permission to
#                    the given database. Defaults to
#                    'postgres'. Anyway, Munin must be told which user
#                    this plugin should be run as.
#       dbpass     - The corresponding password, if
#                    applicable. Default to undef. Remember that
#                    pg_hba.conf must be configured accordingly.
#
# The config variables need to be write like this :
# [pg_foobase*]
# user foouser
# env.dbname foobase
#
# Magic markers
#%# family=auto
#%# capabilities=autoconf

use strict;
use DBI;
use vars qw ( $debug $configure  );

my $dbhost = $ENV{'dbhost'} || '';
my $dbname = $ENV{'dbname'} || 'template1';
my $dbuser = $ENV{'dbuser'} || 'postgres';
my $dbport = $ENV{'dbport'} || '5432';
my $dbpass = $ENV{'dbpass'} || '';
my $statscope = $ENV{'statscope'} || 'user';

my $dsn = "DBI:Pg:dbname=$dbname";
$dsn   .=";host=$dbhost;port=$dbport" if $dbhost;

if (exists $ARGV[0]) {
  if ($ARGV[0] eq 'autoconf') {
    # Check for DBD::Pg
    if (! eval "require DBD::Pg;") {
      print "no (DBD::Pg not found)";
      exit 1;
    }
    my $dbh = DBI->connect ($dsn,
                            $dbuser,
                            $dbpass,
                            {RaiseError =>1});
    if ($dbh) {
      print "yes\n";
      exit 0;
    } else {
      print "no Unable to access Database $dbname on host $dbhost as user $dbuser.\nError returned was: ". $DBI::errstr;
      exit 1;
    }
  } elsif ($ARGV[0] eq 'debug') {
    # Set debug flag
    $debug = 1;
  } elsif ($ARGV[0] eq 'config') {
    # Set config flag
    $configure = 1;
  }
}

if ($configure) {
	print "graph_title PostgreSQL database read hitratio from $dbname\n";
	print "graph_args --upper-limit 110 -l 0\n";
	print "graph_vlabel %\n";
	print "graph_category Postgresql\n";
	print "graph_info This graph shows the percentage of blocks read from the cache\n";
	print "read_hitratio.label Cache hitratio\n";
	print "read_hitratio.type GAUGE\n";
	print "read_hitratio.draw LINE2\n";
} else {
  print "# $dsn\n" if $debug;
  my $dbh = DBI->connect ($dsn,
                          $dbuser,
                          $dbpass,
                          {RaiseError =>1});
  unless($dbh) {
    die ("no Unable to access Database $dbname on host $dbhost as user $dbuser.\nError returned was: ". $DBI::errstr."\n");
  }
  my $sql = "select blks_read,blks_hit from pg_stat_database where datname=?;";
  print "# $sql\n" if $debug;
  my $sth = $dbh->prepare($sql);
  $sth->execute($dbname);
  printf ("# Rows: %d\n",  $sth->rows) if $debug;
  if ($sth->rows > 0) {
    my ($blks_read,$blks_hit) = $sth->fetchrow_array();
    my $read_hitratio =  ($blks_hit/($blks_read+$blks_hit))*100;
    print "read_hitratio.value $read_hitratio\n";
  }
}
exit 0;
