RRDs - Access RRDtool as a shared module

  use RRDs;
  RRDs::error
  RRDs::last ...
  RRDs::info ...
  RRDs::create ...
  RRDs::update ...
  RRDs::updatev ...
  RRDs::graph ...
  RRDs::fetch ...
  RRDs::tune ...
  RRDs::times(start, end)

This module accesses RRDtool functionality directly from within perl. The arguments to the functions listed in the SYNOPSIS are explained in the regular RRDtool documentation. The commandline call

 rrdtool update mydemo.rrd --template in:out N:12:13

gets turned into

 RRDs::update ("mydemo.rrd", "--template", "in:out", "N:12:13");

Note that

 --template=in:out

is also valid.

The RRDs::times function takes two parameters: a start and end time. These should be specified in the AT-STYLE TIME SPECIFICATION format used by RRDtool. See the rrdfetch documentation for a detailed explanation on how to specify time.

The RRD functions will not abort your program even when they can not make sense out of the arguments you fed them.

The function RRDs::error should be called to get the error status after each function call. If RRDs::error does not return anything then the previous function has completed its task successfully.

 use RRDs;
 RRDs::update ("mydemo.rrd","N:12:13");
 my $ERR=RRDs::error;
 die "ERROR while updating mydemo.rrd: $ERR\n" if $ERR;

The functions RRDs::last, RRDs::graph, RRDs::info, RRDs::fetch and RRDs::times return their findings.

RRDs::last returns a single INTEGER representing the last update time.

 $lastupdate = RRDs::last ...

RRDs::graph returns an pointer to an ARRAY containing the x-size and y-size of the created image and results of the PRINT arguments.

 ($averages,$xsize,$ysize) = RRDs::graph ...
 print "Imagesize: ${xsize}x${ysize}\n";
 print "Averages: ", (join ", ", @$averages);

RRDs::info returns a pointer to a hash. The keys of the hash represent the property names of the RRD and the values of the hash are the values of the properties.

 $hash = RRDs::info "example.rrd";
 foreach my $key (keys %$hash){
   print "$key = $$hash{$key}\n";
 }

RRDs::updatev also returns a pointer to hash. The keys of the hash are concatenated strings of a timestamp, RRA index, and data source name for each consolidated data point (CDP) written to disk as a result of the current update call. The hash values are CDP values.

RRDs::fetch is the most complex of the pack regarding return values. There are 4 values. Two normal integers, a pointer to an array and a pointer to a array of pointers.

  my ($start,$step,$names,$data) = RRDs::fetch ... 
  print "Start:       ", scalar localtime($start), " ($start)\n";
  print "Step size:   $step seconds\n";
  print "DS names:    ", join (", ", @$names)."\n";
  print "Data points: ", $#$data + 1, "\n";
  print "Data:\n";
  foreach my $line (@$data) {
    print "  ", scalar localtime($start), " ($start) ";
    $start += $step;
    foreach my $val (@$line) {
      printf "%12.1f ", $val;
    }
    print "\n";
  }

RRDs::times returns two integers which are the number of seconds since epoch (1970-01-01) for the supplied start and end arguments, respectively.

See the examples directory for more ways to use this extension.

If you are manipulating the TZ variable you should also call the posixs function tzset to initialize all internal state of the library for properly operating in the timezone of your choice.

 use POSIX qw(tzset);
 $ENV{TZ} = 'CET';   
 POSIX::tzset();

Tobias Oetiker <oetiker@ee.ethz.ch>