========
Features
========
PyRRD lets you use RRDTool from Python code that takes advantage of standard
object-oriented patterns. The makes the programmatic usage of RRDTool much
easier and reusable.
A quick review of features is available at the project wiki [#]_ . Example
code with graph image output is also available on the wiki [#]_ .
============
Introduction
============
PyRRD is an object-oriented wrapper for the command line graphing and
round-robin database utility, rrdtool [#]_ . PyRRD originally had two design
goals:
1. provide an interface to rrdtool that Python programmers would love, and
2. not depend upon the Python bindings for rrdtool.
The reasons for the former are obvious. The motivation for the latter were the
many people who had difficulty compiling the rrdtool bindings on their
operating system of choice.
Even though PyRRD's original purpose was to help those without the bingins, the
project now offers support for those with the bindings installed. As such,
users may enjoy both the speed benefits from the bindings as well as the API
usability from PyRRD.
For docs, see the docstrings at the beginning of each class (and many of the
functions). They not only contain many of the standard RRDTool docs, but they
contain doctests which give you a hands-on, how-it-works understanding of
actual usage.
For those curious about the motivation for creating PyRRD, perhaps some
background would be in order. Originally, there were only two ways to use
RRDTool from Python:
1. using the Python bindings which were difficult to compile and use, or
2. making system calls to the "rrdtool" executable from Python, passing
it all the parameters it needed.
Option #1 was often difficult or impossible for many folks to get running on
their preferred operating system. But even if one was able to compile it and
run it, usage was very cumbersome and designed to work like the command line
tool and the C interface, not like most people typically use Python.
Now, with PyRRD, there are two additional ways to use RRDTool from Python:
3. an object-oriented interface that wraps system calls (Popen) to the
rrdtool binary, and
4. the same object-oriented interface that wraps the cumbersome rrdtool
Python bindings.
============
Dependencies
============
Some parts of PyRRD make use of ElementTree for XML processing. If you have
Python 2.5 or greater, PyRRD will use xml.etree. If your Python version is less
than 2.5 and you want to use features that depend on XML processing (such as
dump function and the fetch/info methods), you will need to install
the ElementTree library [#]_ .
============
Installation
============
PyRRD is installed in the usual way::
python setup.py install
You may also use PyRRD without installing it as long as you have ./ in your
PYTHONPATH and you are in the top-level directory (which has the pyrrd child
directory).
=====
Usage
=====
Create an RRD file programmatically::
>>> from pyrrd.rrd import DataSource, RRA, RRD
>>> filename = '/tmp/test.rrd'
>>> dataSources = []
>>> roundRobinArchives = []
>>> dataSource = DataSource(
... dsName='speed', dsType='COUNTER', heartbeat=600)
>>> dataSources.append(dataSource)
>>> roundRobinArchives.append(RRA(cf='AVERAGE', xff=0.5, steps=1, rows=24))
>>> roundRobinArchives.append(RRA(cf='AVERAGE', xff=0.5, steps=6, rows=10))
>>> myRRD = RRD(
... filename, ds=dataSources, rra=roundRobinArchives, start=920804400)
>>> myRRD.create()
Let's check to see that the file exists::
>>> import os
>>> os.path.isfile(filename)
True
Let's see how big it is (depending upon RRDTool version, the byte count can
change, so we'll just get a general sense)::
>>> bytes = len(open(filename).read())
>>> 800 < bytes < 1200
True
In order to save writes to disk, PyRRD buffers values and then writes the
values to the RRD file at one go::
>>> myRRD.bufferValue('920805600', '12363')
>>> myRRD.bufferValue('920805900', '12363')
>>> myRRD.bufferValue('920806200', '12373')
>>> myRRD.bufferValue('920806500', '12383')
>>> myRRD.update()
Let's add some more data::
>>> myRRD.bufferValue('920806800', '12393')
>>> myRRD.bufferValue('920807100', '12399')
>>> myRRD.bufferValue('920807400', '12405')
>>> myRRD.bufferValue('920807700', '12411')
>>> myRRD.bufferValue('920808000', '12415')
>>> myRRD.bufferValue('920808300', '12420')
>>> myRRD.bufferValue('920808600', '12422')
>>> myRRD.bufferValue('920808900', '12423')
>>> myRRD.update()
If you're curious, you can take a look at your rrd file with the following::
myRRD.info()
The output of that isn't printed here, 'cause it take up too much space.
However, it is very similar to the output of the similarly named rrdtool
command.
In order to create a graph, we'll need some data definitions. We'll also
throw in some calculated definitions and variable definitions for good
measure::
>>> from pyrrd.graph import DEF, CDEF, VDEF, LINE, AREA, GPRINT
>>> def1 = DEF(rrdfile=myRRD.filename, vname='myspeed',
... dsName=dataSource.name)
>>> cdef1 = CDEF(vname='kmh', rpn='%s,3600,*' % def1.vname)
>>> cdef2 = CDEF(vname='fast', rpn='kmh,100,GT,kmh,0,IF')
>>> cdef3 = CDEF(vname='good', rpn='kmh,100,GT,0,kmh,IF')
>>> vdef1 = VDEF(vname='mymax', rpn='%s,MAXIMUM' % def1.vname)
>>> vdef2 = VDEF(vname='myavg', rpn='%s,AVERAGE' % def1.vname)
>>> line1 = LINE(value=100, color='#990000', legend='Maximum Allowed')
>>> area1 = AREA(defObj=cdef3, color='#006600', legend='Good Speed')
>>> area2 = AREA(defObj=cdef2, color='#CC6633', legend='Too Fast')
>>> line2 = LINE(defObj=vdef2, color='#000099', legend='My Average',
... stack=True)
>>> gprint1 = GPRINT(vdef2, '%6.2lf kph')
Color is the spice of life. Let's spice it up a little::
>>> from pyrrd.graph import ColorAttributes
>>> ca = ColorAttributes()
>>> ca.back = '#333333'
>>> ca.canvas = '#333333'
>>> ca.shadea = '#000000'
>>> ca.shadeb = '#111111'
>>> ca.mgrid = '#CCCCCC'
>>> ca.axis = '#FFFFFF'
>>> ca.frame = '#AAAAAA'
>>> ca.font = '#FFFFFF'
>>> ca.arrow = '#FFFFFF'
Now we can create a graph for the data in our RRD file::
>>> from pyrrd.graph import Graph
>>> graphfile = "/tmp/rrdgraph.png"
>>> g = Graph(graphfile, start=920805000, end=920810000,
... vertical_label='km/h', color=ca)
>>> g.data.extend([def1, cdef1, cdef2, cdef3, vdef1, vdef2, line1, area1,
... area2, line2, gprint1])
>>> g.write()
Let's make sure it's there::
>>> os.path.isfile(graphfile)
True
Let's get a sense of the byte size::
>>> bytes = len(open(graphfile).read())
>>> bytes != 0
True
>>> 8000 < bytes < 10400
True
Open that up in your favorite image browser and confirm that the appropriate
RRD graph is generated.
Let's clean up the files we've put in the temp directory::
>>> os.unlink(filename)
>>> os.unlink(graphfile)
===============
Python Bindings
===============
In addition to the command line tool, PyRRD also supports using the Python
bindings, if you have them installed. Let's set some stuff up like we did in
the previous example::
>>> filename = '/tmp/test.rrd'
>>> dataSources = []
>>> roundRobinArchives = []
>>> dataSource = DataSource(
... dsName='speed', dsType='COUNTER', heartbeat=600)
>>> dataSources.append(dataSource)
>>> roundRobinArchives.append(RRA(cf='AVERAGE', xff=0.5, steps=1, rows=24))
>>> roundRobinArchives.append(RRA(cf='AVERAGE', xff=0.5, steps=6, rows=10))
Usage is identical to the standard PyRRD usage, with the exception of object
construction::
>>> from pyrrd.backend import bindings
>>> myRRD = RRD(filename, ds=dataSources, rra=roundRobinArchives,
... backend=bindings)
>>> myRRD.create()
Note that since the Graph module is its own beast, you will need to indicate
whether you want to use the bindings or the external backend when you graph as
well::
>>> from pyrrd.graph import Graph
>>> graphfile = "/tmp/rrdgraph.png"
>>> g = Graph(graphfile, start=920805000, end=920810000,
... vertical_label='km/h', color=ca, backend=bindings)
>>> g.data.extend([def1, cdef1, cdef2, cdef3, vdef1, vdef2, line1, area1,
... area2, line2, gprint1])
>>> g.write()
Everything else is the same. Let's check to see that the file exists, and then
we'll cleanup::
>>> import os
>>> os.path.isfile(filename)
True
>>> os.unlink(filename)