RRDs(3) User Contributed Perl Documentation RRDs(3)

NAME

RRDs - Access RRDtool as a shared module

SYNOPSIS

use RRDs;
RRDs::error
RRDs::last ...
RRDs::info ...
RRDs::create ...
RRDs::update ...
RRDs::updatev ...
RRDs::graph ...
RRDs::fetch ...
RRDs::tune ...
RRDs::times(start, end)
RRDs::dump ...
RRDs::restore ...
RRDs::flushcached ...
RRDs::register_fetch_cb ...
$RRDs::VERSION

DESCRIPTION

Calling Sequence

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 command line 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.

Error Handling

The RRD functions will not abort your program even when they cannot
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;

Return Values

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 ARRAY containing the x-size and y-size of the
created image and a pointer to an array with the results of the PRINT
arguments.

($result_arr,$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::graphv takes the same parameters as RRDs::graph but it returns
a pointer to hash. The hash returned contains meta information about
the graph. Like its size as well as the position of the graph area on
the image. When calling with '-' as the filename then the contents
of the graph will be returned in the hash as well (key 'image').

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 an 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";
for my $line (@$data) {
print " ", scalar localtime($start), " ($start) ";
$start += $step;
for my $val (@$line) {
printf "%12.1f ", $val;
}
print "\n";
}

RRDs::xport exposes the rrdxport functionality and returns data with
the following structure:

my ($start,$end,$step,$cols,$names,$data) = RRDs::xport ...

# $start : timestamp
# $end : timestamp
# $step : seconds
# $cols : number of returned columns
# $names : arrayref with the names of the columns
# $data : arrayref of arrayrefs with the data (first index is time, second is column)

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.

Fetch Callback Function

Normally when using graph, xport or fetch the data you see will come
from an actual rrd file. Some people who like the look of rrd
charts, therefore export their data from a database and then load it
into an rrd file just to be able to call rrdgraph on it. Using a
custom callback, you can supply your own code for handling the data
requests from graph, xport and fetch.

To do this, you have to first write a fetch function in perl, and
then register this function using "RRDs::fetch_register_callback".

Finally you can use the pseudo path name cb//[filename] to tell
rrdtool to use your callback routine instead of the normal rrdtool
fetch function to organize the data required.

The callback function must look like this:

sub fetch_callback {
my $args_hash = shift;
# {
# filename => 'cb//somefilename',
# cd => 'AVERAGE',
# start => 1401295291,
# end => 1401295591,
# step => 300 }

# do some clever thing to get that data ready

return {
start => $unix_timestamp,
step => $step_width,
data => {
dsName1 => [ value1, value2, ... ],
dsName2 => [ value1, value2, ... ],
dsName3 => [ value1, value2, ... ],
}
};
}

NOTE

If you are manipulating the TZ variable you should also call the
POSIX function tzset(3) to initialize all internal states of the
library for properly operating in the timezone of your choice.

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

AUTHOR

Tobias Oetiker <tobi@oetiker.ch>

perl v5.34.0 2022-03-14 RRDs(3)