FUNCTIONS

my $rrd = RRDTool::OO->new( file => $file )

The constructor hooks up with an existing RRD database file $file, but doesn't create a new one if none exists. That's what the "create()" methode is for. Returns a "RRDTool::OO" object, which can be used to get access to the following methods.

$rrd->create( ... )

Creates a new round robin database (RRD). A RRD consists of one or more data sources and one or more archives:

    $rrd->create(
         step        => 60,
         data_source => { name      => "mydatasource",
                          type      => "GAUGE" },
         archive     => { rows      => 5 });
    

This defines a RRD database with a step rate of 60 seconds in between primary data points. Additionally, the RRD start time can be specified by specifying a "start" parameter.

It also sets up one data source named "my_data_source" of type "GAUGE", telling rrdtool to use values of data samples as-is, without additional trickery.

And it creates a single archive with a 1:1 mapping between primary data points and archive points, with a capacity to hold five data points.

The RRD's "step" parameter is optional, and will be set to 300 seconds by rrdtool by default.

In addition to the mandatory settings for "name" and "type", "data_source" parameter takes the following optional parameters: "min" (minimum input, defaults to "U"), "max" (maximum input, defaults to "U"), "heartbeat" (defaults to twice the RRD's step rate).

Archives expect at least one parameter, "rows" indicating the number of data points the archive is configured to hold. If nothing else is set, rrdtool will store primary data points 1:1 in the archive.

If you want to combine several primary data points into one archive point, specify values for "cpoints" (the number of points to combine) and "cfunc" (the consolidation function) explicitly:

    $rrd->create(
         step        => 60,
         data_source => { name      => "mydatasource",
                          type      => "GAUGE" },
         archive     => { rows      => 5,
                          cpoints   => 10,
                          cfunc     => 'AVERAGE',
                        });
    

This will collect 10 data points to form one archive point, using the calculated average, as indicated by the parameter "cfunc" (Consolidation Function, CF). Other options for "cfunc" are "MIN", "MAX", and "LAST".

If you're defining multiple data sources or multiple archives, just provide them in this manner:

       # Define the RRD
    my $rc = $rrd->create(
        step        => 60,
        data_source => { name      => 'load1',
                         type      => 'GAUGE',
                       },
        data_source => { name      => 'load2',
                         type      => 'GAUGE',
                       },
        archive     => { rows      => 5,
                         cpoints   => 10,
                         cfunc     => 'AVERAGE',
                        },
        archive     => { rows      => 5,
                         cpoints   => 10,
                         cfunc     => 'MAX',
                        },
    );
    

$rrd->update( ... )

Update the round robin database with a new data sample, consisting of a value and an optional time stamp. If called with a single parameter, like in

    $rrd->update($value);
    

then the current timestamp and the defined $value will be used. If "update" is called with a named parameter list like in

    $rrd->update(time => $time, value => $value);
    

then the given timestamp $time is used along with the given value $value.

When updating multiple data sources, use the "values" parameter (instead of "value") and pass an arrayref:

    $rrd->update(time => $time, values => [$val1, $val2, ...]);
    

This way, rrdtool expects you to pass in the data values in exactly the same order as the data sources were defined in the "create" method. If that's not the case, then the "values" parameter also accepts a hashref, mapping data source names to values:

    $rrd->update(time => $time, 
                 values => { $dsname1 => $val1, 
                             $dsname2 => $val2, ...});
    

"RRDTool::OO" will transform this automagically into "RRDTool's" template syntax.

$rrd->updatev( ... )

This is identical to "update", but uses rrdtool's updatev function internally. The only difference is when using the "print_results" method described below, which then contains additional information.

$rrd->fetch_start( ... )

Initializes the iterator to fetch data from the RRD. This works nicely without any parameters if your archives are using a single consolidation function (e.g. "MAX"). If there's several archives in the RRD using different consolidation functions, you have to specify which one you want:

    $rrd->fetch_start(cfunc => "MAX");
    

Other options for "cfunc" are "MIN", "AVERAGE", and "LAST".

"fetch_start" features a number of optional parameters: "start", "end" and "resolution".

If the "start" time parameter is omitted, the fetch starts 24 hours before the end of the archive. Also, an "end" time can be specified:

    $rrd->fetch_start(start => time()-10*60,
                      end   => time());
    

The third optional parameter, "resolution" defaults to the highest resolution available and can be set to a value in seconds, specifying the time interval between the data samples extracted from the RRD. See the "rrdtool fetch" manual page for details.

Development note: The current implementation fetches all values from the RRA in one swoop and caches them in memory. This might change in the future, to cache only the last timestamp and keep fetching from the RRD with every "fetch_next()" call.

$rrd->fetch_skip_undef()

rrdtool doesn't remember the time the first data sample went into the archive. So if you run a rrdtool fetch with a start time of 24 hours ago and you've only submitted a couple of samples to the archive, you'll see many "undef" values.

Starting from the current iterator position (or at the specified "start" time immediately after a "fetch_start()"), "fetch_skip_undef()" will skip all "undef" values in the RRA and positions the iterator right before the first defined value. If all values in the RRA are undefined, the a following "$rrd->fetch_next()" will return "undef".

($time, $value, ...) = $rrd->fetch_next()

Gets the next row from the RRD iterator, initialized by a previous call to "$rrd->fetch_start()". Returns the time of the archive point along with all values as a list.

Note that there might be more than one value coming back from "fetch_next" if the RRA defines more than one datasource):

    I<($time, @values_of_all_ds) = $rrd-E<gt>fetch_next()>
    

It is not possible to fetch only a specific datasource, as rrdtool doesn't provide this.

($time, $value, ...) = $rrd->fetch_next()

$rrd->graph( ... )

If there's only one data source in the RRD, drawing a nice graph in an image file on disk is as easy as

    $rrd->graph(
      image          => $image_file_name,
      vertical_label => 'My Salary',
      draw           => { thickness => 2,
                          color     => 'FF0000',
                          legend    => 'Salary over Time',
                        },
    );
    

This will assume a start time of 24 hours before now and an end time of now. Specify "start" and "end" explicitly to be clear:

    $rrd->graph(
      image          => $image_file_name,
      vertical_label => 'My Salary',
      start          => time() - 24*3600,
      end            => time(),
      draw           => { thickness => 2,
                          color     => 'FF0000',
                          legend    => 'Salary over Time',
                        },
    );
    

As always, "RRDTool::OO" will pick reasonable defaults for parameters not specified. The values for data source and consolidation function default to the first values it finds in the RRD. If there are multiple datasources in the RRD or multiple archives with different values for "cfunc", just specify explicitly which one to draw:

    $rrd->graph(
      image          => $image_file_name,
      vertical_label => 'My Salary',
      draw           => {
        thickness => 2,
        color     => 'FF0000',
        dsname    => "load",
        cfunc     => 'MAX'},
    );
    

If "draw" doesn't define a "type", it defaults to "line". If you don't want to define a type (because the graph shouldn't be drawn), use "type => "hidden"". Other values are "area" for solid colored areas. The "stack" type (for graphical values stacked on top of each other) has been deprecated sind rrdtool-1.2, but RRDTool::OO still supports it by transforming it into an 'area' type with a 'stack' option.

And you can certainly have more than one graph in the picture:

    $rrd->graph(
      image          => $image_file_name,
      vertical_label => 'My Salary',
      draw           => {
        type      => 'area',
        color     => 'FF0000', # red area
        dsname    => "load",
        cfunc     => 'MAX'},
      draw        => {
        type      => 'area',
        stack     => 1,
        color     => '00FF00', # a green area stacked on top of the red one 
        dsname    => "load",
        cfunc     => 'AVERAGE'},
    );
    

Graphs may assemble data from different RRD files. Just specify which file you want to draw the data from, using "draw":

    $rrd->graph(
      image          => $image_file_name,
      vertical_label => 'Network Traffic',
      draw           => {
        file      => "file1.rrd",
        legend    => "First Source",
      },
      draw        => {
        file      => "file2.rrd",
        type      => 'area',
        stack     => 1,
        color     => '00FF00', # a green area stacked on top of the red one 
        dsname    => "load",
        legend    => "Second Source",
        cfunc     => 'AVERAGE'
      },
    );
    

If a "file" parameter is specified per "draw", the defaults for "dsname" and "cfunc" are fetched from this file, not from the file that's attached to the "RRDTool::OO" object $rrd used.

Graphs may also consist of algebraic calculations of previously defined graphs. In this case, graphs derived from real data sources need to be named, so that subsequent "cdef" definitions can refer to them and calculate new graphs, based on the previously defined graph:

    $rrd->graph(
      image          => $image_file_name,
      vertical_label => 'Network Traffic',
      draw           => {
        type      => 'line',
        color     => 'FF0000', # red line
        dsname    => 'load',
        name      => 'firstgraph',
        legend    => 'Unmodified Load',
      },
      draw        => {
        type      => 'line',
        color     => '00FF00', # green line
        cdef      => "firstgraph,2,*",
        legend    => 'Load Doubled Up',
      },
    );
    

Note that the second "draw" doesn't refer to a datasource "dsname" (nor does it fall back to the default data source), but defines a "cdef", performing calculations on a previously defined draw named "firstgraph". The calculation is specified using RRDTool's reverse polish notation, where instructions are separated by commas ("firstgraph,2,*" simply multiplies "firstgraph"'s values by 2).

On a global level, in addition to the "vertical_label" parameter shown in the examples above, "graph" offers a plethora of parameters:

"vertical_label", "title", "start", "end", "x_grid", "y_grid", "alt_y_grid", "no_minor", "alt_y_mrtg", "alt_autoscale", "alt_autoscale_max", "base", "units_exponent", "units_length", "width", "height", "interlaced", "imginfo", "imgformat", "overlay", "unit", "lazy", "rigid", "lower_limit", "upper_limit", "logarithmic", "color", "no_legend", "only_graph", "force_rules_legend", "title", "step".

Some options (e.g. "alt_y_grid") don't expect values, they need to be specified like

    alt_y_grid => undef
    

in order to be passed properly to RRDTool.

The "color" option expects a reference to a hash with various settings for the different graph areas: "back" (background), "canvas", "shadea" (left/top border), "shadeb" (right/bottom border), "grid", "mgrid" major grid, "font", "frame" and "arrow":

    $rrd->graph(
      ...
      color          => { back   => '#0e0e0e',
                          arrow  => '#ff0000',
                          canvas => '#eebbbb',
                        },
      ...
    );
    

Fonts for various graph elements may be specified in "font" blocks, which must either name a TrueType font file or a PDF/Postscript font name. You may optionally specify a size and element name (defaults to DEFAULT, which to RRD means "use this font for everything). Example:

    font  => {
        name => "/usr/openwin/lib/X11/fonts/TrueType/GillSans.ttf",
        size => 16,
        element => "title"
    }
    

Please check the RRDTool documentation for a detailed description on what each option is used for:

    http://people.ee.ethz.ch/~oetiker/webtools/rrdtool/manual/rrdgraph.html
    

Sometimes it's useful to print max, min or average values of a given graph at the bottom of the chart or to STDOUT. That's what "gprint" and "print" options are for. They are printing variables which are defined as "vdef"s somewhere else:

    $rrd->graph(
      image          => $image_file_name,
          # Real graph
      draw           => {
        name      => "first_draw",
        dsname    => "load",
        cfunc     => 'MAX'
      },

        # vdef for calculating average of real graph
      draw           => {
        type      => "hidden",
        name      => "average_of_first_draw",
        vdef      => "first_draw,AVERAGE"
      },

      gprint         => {
        draw      => 'average_of_first_draw',
        format    => 'Average=%lf',
      },
    );
    

The "vdef" performs a calculation, specified in RPN notation, on a real graph, which it refers to. It uses a hidden graph for this.

The "gprint" option then refers to the "vdef" virtual graph and prints "Average=x.xx" at the bottom of the graph, showing what the average value of graph "first_draw" is.

To write comments to the graph (like gprints, but with no associated RRD data source) use "comment", like this:

    $rrd->graph(
      image          => $image_file_name,
      draw           => {
        name      => "first_draw",
        dsname    => "load",
        cfunc     => 'MAX'},
      comment        => "Remember, 83% of all statistics are made up",
    );
    

Multiple comment lines can be specified in a single comment specification like this:

     comment => [ "All the king's horses and all the king's men\\n",
                  "couldn't put Humpty together again.\\n",
                ],
    

Vertical rules (lines) may be placed into the graph by using a "vrule" block like so:

       vrule => { time => time()-3600, }
    

These can be useful for indicating when the most recent day on the graph started, for example.

vrules can have a color specification (they default to black) and also an optional legend string specified:

      vrule => { time => $first_thing_today,
                 color => "#0000ff",
                 legend => "When we crossed midnight"
               },
    

hrules can have a color specification (they default to black) and also an optional legend string specified:

      hrule => { value => $numeric_value,
                 color => "#0000ff",
                 legend => "a static line at your value"
               },
    

Horizontal rules can be added by using a "line" block like in

    line => { 
        value   => "fixed num value or draw name",
        color   => "#0000ff",
        legend  => "a blue horizontal line",
        width   => 120,
        stack   => 1,
    }
    

If instead of a horizontal line, a rectangular area is supposed to be added to the graph, use an "area" block:

    area => { 
        value   => "fixed num value or draw name",
        color   => "#0000ff",
        legend  => "a blue horizontal line",
        stack   => 1,
    }
    

The "graph" method can also generate tickmarks (vertical lines) for every defined value, using the "tick" option:

    tick => {
        draw    => "drawname",
        color   => "#0000ff",
        legend  => "a blue horizontal line",
        stack   => 1,
    }
    

The graph may be shifted relative to the time axis:

    shift => {
        draw    => "drawname",
        offset  => $offset,
    }
    

$rrd->graphv( ... )

This is identical to "graph", but uses rrdtool's graphv function internally. The only difference is when using the "print_results" method described below, which then contains additional information. Be aware that rrdtool 1.3 is required for "graphv" to work.

$rrd->dump()

Available as of rrdtool 1.0.49.

Dumps the RRD in XML format to STDOUT. If you want to dump it into a file instead, do this:

    my $pid;

    unless ($pid = open DUMP, "-|") {
      die "Can't fork: $!" unless defined $pid;
      $rrd->dump();
      exit 0;
    }

    waitpid($pid, 0);

    open OUT, ">out";
    print OUT $_ for <DUMP>;
    close OUT;
    

my $hashref = $rrd->xport(...)

Feed a perl structure with RRA data (Cf. rrdxport man page).

    my $results = $rrd->xport(
        start => $start_time,
        end => $end_time ,
        step => $step,
        def => [{
            vname => "load1_vname",
            file => "foo",
            dsname => "load1",
            cfunc => "MAX",
        },
        {
            vname => "load2_vname",
            file => "foo",
            dsname => "load2",
            cfunc => "MIN",
        }],

        cdef => [{
            vname => "load2_vname_multiply",
            rpn => "load2_vname,2,*",
        }],

        xport => [{
            vname => "load1_vname",
            legend => "it_s_gonna_be_legend_",
        },
        {
            vname => "load2_vname",
            legend => "wait_for_it",
        },
        {
            vname => "load2_vname_multiply",
            legend => "___dary",
        }],
    );

    my $data = $results->{data};
    my $metadata = $results->{meta};

    print "### METADATA ###\n";
    print "StartTime: $metadata->{start}\n";
    print "EndTime: $metadata->{end}\n";
    print "Step: $metadata->{step}\n";
    print "Number of data columns: $metadata->{columns}\n";
    print "Number of data rows: $metadata->{rows}\n";
    print "Legend: ", join(", ", @{$metadata->{legend}}), "\n";

    print "\n### DATA ###\n";
    foreach my $entry (@$data) {
        my $entry_timestamp = shift(@$entry);
        print "[$entry_timestamp] ", join(" ", @$entry), "\n";
    }
    

my $hashref = $rrd->info()

Grabs the RRD's meta data and returns it as a hashref, holding a map of parameter names and their values.

my $time = $rrd->first()

Return the RRD's first update time.

my $time = $rrd->last()

Return the RRD's last update time.

$rrd->restore(xml => "file.xml")

Available as of rrdtool 1.0.49.

Restore a RRD from a "dump". The "xml" parameter specifies the name of the XML file containing the dump. If the optional flag "range_check" is set to a true value, "restore" will make sure the values in the RRAs do not exceed the limits defined for the different datasources:

    $rrd->restore(xml => "file.xml", range_check => 1);
    

$rrd->tune( ... )

Alter a RRD's data source configuration values:

        # Set the heartbeat of the RRD's only datasource to 100
    $rrd->tune(heartbeat => 100);

        # Set the minimum of DS 'load' to 1
    $rrd->tune(dsname => 'load', minimum => 1);

        # Set the maximum of DS 'load' to 10
    $rrd->tune(dsname => 'load', maximum => 10);

        # Set the type of DS 'load' to AVERAGE
    $rrd->tune(dsname => 'load', type => 'AVERAGE');

        # Set the name of DS 'load' to 'load2'
    $rrd->tune(dsname => 'load', name => 'load2');
    

$rrd->error_message()

Return the message of the last error that occurred while interacting with "RRDTool::OO".

Aberrant behavior detection

Using a fairly elaborate algorithm not only allows it to find out if a data source produces a value that exceeds a certain fixed threshold. The algorithm constantly adapts its parameters to the input data and acts dynamically on slowly changing values.

The "alpha" parameter specifies the baseline and lies between 0 and 1. Values close to 1 specify that most recent values have the most weight on the prediction, whereas values close to 0 indicate that past values carry higher weight.

On top of that, ABD can deal with data input that displays continuously rising values (slope). The "beta" parameters, again between 0 and 1, specifies whether past values or more recent values carry the most weight.

And, furthermore, it deals with seasonal cycles, so it won't freak out if there's a daily peak at noon. The "gamma" parameter indicates this, if you don't specify it, it defaults to the value of "alpha".

In the easiest case, an RRA with aberrant behavior detection can be created like

        # Create a round-robin database
    $rrd->create(
         step        => 1,  # one-second intervals
         data_source => { name      => "mydatasource",
                          type      => "GAUGE" },
         hwpredict   => { rows => 3600,
                        },
    );

where "alpha" and "beta" default to 0.5, and the "seasonal_period" defaults to 1/5 of the rows number.

"rows" is the number of primary data points that are stored in the RRA before a wrap-around happens. Note that with ABD enabled, RRDTool won't consolidate the data from a data source before stuffing it into the HWPREDICT RRAs, as the whole point of ABD is to smooth unfiltered data and predict future values.

A violation happens if a new measured value falls outside of the prediction. If "threshold" or more violations happen within "window_length", an error is reported to the FAILURES RRA. "threshold" defaults to 7, "window_length" to 9.

A more elaborate RRD could be defined as

        # Create a round-robin database
    $rrd->create(
         step        => 1,  # one-second intervals
         data_source => { name      => "mydatasource",
                          type      => "GAUGE" },
         hwpredict   => { rows          => 3600,
                          alpha         => 0.1,
                          beta          => 0.1,
                          gamma         => 0.1,
                          threshold     => 7,
                          window_length => 9,
                        },
    );

If you want to peek under the hood (not that you need to, just for your entertainment), with the specification above, RRDTool::OO will create the following five RRAs according to the RRDtool specification and fill in these values:

    * RRA:HWPREDICT:rows:alpha:beta:seasonal_period:rra-num
    * RRA:SEASONAL:seasonal period:gamma:rra-num
    * RRA:DEVSEASONAL:seasonal period:gamma:rra-num
    * RRA:DEVPREDICT:rows:rra-num
    * RRA:FAILURES:rows:threshold:window_length:rra-num

The "rra-num" argument is an internal index referencing other RRAs (for example, HWPREDICT references SEASONAL), but this will be taken care of automatically by RRDTool::OO with no user interaction required whatsoever.

Development Status

"rrdresize", "xport", "rrdcgi".

Print Output

    $rrd->graph(
      image          => "mygraph.png",
      start          => $start_time,

      # ...

      draw           => {
          type      => "hidden",
          name      => "in95precent",
          vdef      => "firstdraw,95,PERCENT"
      },

      print         => {
          draw      => 'in95percent',
          format    => "95 Percent Result = %3.2lf",
        },

      # ...

captures the print data internally. To get access to a reference to the array containing the different pieces of data written in this way, call

    my $array_ref = $rrd->print_results();

If no print output is available, the array referenced by $array_ref is empty.

If the "graphv" function is used instead of "graph", the return value of print_results is a hashref containing the same information in the "print" keys, along with additional keys containing detailed information on the graph. See "rrdtool" documentation for more detail. Here is an example:

    use Data::Dumper;

    $rrd -> graphv (
      image          => "-",
      start          => $start_time,

      # ...

    my $hash_ref = $rrd->print_results();

    print Dumper $hash_ref;
    $VAR1 = {
          'print[2]' => '1600.00',
          'value_min' => '200',
          'image_height' => 64,
          'graph_height' => 10,
          'print[1]' => '3010.18',
          'graph_end' => 1249391462,
          'print[3]' => '1600.00',
          'graph_left' => 51,
          'print[4]' => '2337.29',
          'print[0]' => '305.13',
          'value_max' => '10000',
          'graph_width' => 10,
          'image_width' => 91,
          'graph_top' => 22,
          'image' => '#PNG
                     [...lots of binary rubbish your terminal won't like...]
                     ',
          'graph_start' => 1217855462
        };

In this case, the option (image => "-") has been used to create the hash key with the same name, the value of which actually contains the BLOB of the image itself. This is useful when image needs to be passed to other modules (e.g. Image::Magick), instead of writing it to disk. Be aware that rrdtool 1.3 is required for "graphv" to work.

Error Handling

This behaviour can be overridden by calling the constructor with the "raise_error" flag set to false:

    my $rrd = RRDTool::OO->new(
        file        => "myrrdfile.rrd",
        raise_error => 0,
    );

In this mode, RRDTool's methods will just pass back values returned from the underlying "RRDs" functions if an error happens (usually 1 if successful and "undef" if an error occurs).

Debugging

    use Log::Log4perl qw(:easy);

    Log::Log4perl->easy_init({
        level    => $DEBUG
    });

If you're interested particularly in rrdtool commands issued by "RRDTool::OO" while you're operating it, just enable the category "rrdtool":

    Log::Log4perl->easy_init({
        level    => $INFO, 
        category => 'rrdtool',
        layout   => '%m%n',
    });

This will display all "rrdtool" commands that "RRDTool::OO" submits to the shared library. Let's turn it on for the code snippet in the SYNOPSIS section of this manual page and watch the output:

    rrdtool create myrrdfile.rrd --step 1 \
            DS:mydatasource:GAUGE:2:U:U RRA:MAX:0.5:1:5
    rrdtool update myrrdfile.rrd N:1
    rrdtool update myrrdfile.rrd N:2
    rrdtool update myrrdfile.rrd N:3
    rrdtool fetch myrrdfile.rrd MAX

Often handy for cut-and-paste.

Allow New rrdtool Parameters

This might lead to problems, since default, "RRDTool::OO" has its "strict" mode enabled, rejecting all unknown options. This mode is usually helpful, because it catches typos (like "verical_label"), but if you want to use a new rrdtool option, it's in the way.

To work around this problem until a new version of "RRDTool::OO" supports the new parameter, you can use

    $rrd->option_add("graph", "frobnication_level");

to add it to the optional parameter list of the "graph" (or whatever) rrd function. Note that some functions in "RRDTool::OO" have sub-methods, which you can specify with the dash notation. The "graph" method with its various "graph/draw", "graph/color", "graph/font" are notable examples.

And, as a band-aid, you can disable strict mode in these situation by setting the "strict" parameter to 0 in "RRDTool::OO"'s constructor call:

    my $rrd = RRDTool::OO->new(
        strict => 0,
        file   => "myrrdfile.rrd",
    );

Note that "RRDTool::OO" follows the convention that parameters names do not contain dashes, but underscores instead. So, you need to say "vertical_label", not "vertical-label". The underlying rrdtool layer, however, expects dashes, not underscores, which is why "RRDTool::OO" converts them automatically, e.g. transforming "vertical_label" to "--vertical-label" before the underlying rrdtool call happens.

Dry Run Mode

    my $rrd = RRDTool::OO->new(
        file => "myrrdfile.rrd",
        dry_run => 1
    );

With dry_run set to a true value, you can run commands like

    $rrd->create(
          step        => 60,
          data_source => { name      => "mydatasource",
                           type      => "GAUGE" },
          archive     => { rows      => 5 });

but since dry_mode is on, they won't be handed through to the rrdtool layer anymore. Instead, RRDTool::OO allows you to retrieve a reference to the RRDs function it was about to call including its arguments:

    my ($subref, $args) = $rrd->get_exec_env();

You can now examine or modify the subroutine reference $subref or the arguments in the array reference $args. Later, simply call

    $subref->(@$args);

to execute the RRDs function with the modified argument list later. In this case, @$args would contain the following items:

    ("myrrdfile.rrd", "--step", "60", 
     "DS:mydatasource:GAUGE:120:U:U", "RRA:MAX:0.5:1:5")

If you're interested in the RRD function name to be executed, retrieve the third parameter of "get_exec_env":

    my ($subref, $args, $funcname) = $rrd->get_exec_env();