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<p>
<p>This manual is an attempt to assist beginners in understanding the concepts
of RRDtool. It sheds a light on differences between RRDtool and other
databases. With help of an example, it explains the structure of RRDtool
-database. This is followed by an overview of the ``graph'' feature of RRDtool.
+database. This is followed by an overview of the "graph" feature of RRDtool.
At the end, it has sample scripts that illustrate the
usage/wrapping of RRDtool within Shell or Perl scripts.</p>
<p>
database as the perimeter of a circle. Data is added along the
perimeter. When new data reaches the starting point, it overwrites
existing data. This way, the size of an RRDtool database always
-remains constant. The name ``Round Robin'' stems from this behavior.</p>
+remains constant. The name "Round Robin" stems from this behavior.</p>
</li>
<li>
<p>Other databases store the values as supplied. RRDtool can be configured to
DS:mem:GAUGE:600:0:671744 \
RRA:AVERAGE:0.5:12:24 \
RRA:AVERAGE:0.5:288:31</pre>
-<p>This example creates a database named <em>target.rrd</em>. Start time
+<p>This example creates a database named <em class="file">target.rrd</em>. Start time
(1'023'654'125) is specified in total number of seconds since epoch
(time in seconds since 01-01-1970). While updating the database, the
update time is also specified. This update time MUST be large (later)
every step interval, a new value of DS is supplied to update the database.
This value is also called Primary Data Point <strong>(PDP)</strong>. In our example
mentioned above, a new PDP is generated every 300 seconds.</p>
-<p>Note, that if you do NOT supply new datapoints exactly every 300 seconds,
+<p>Note, that if you do NOT supply new data points exactly every 300 seconds,
this is not a problem, RRDtool will interpolate the data accordingly.</p>
<p><strong>DST</strong> (Data Source Type) defines the type of the DS. It can be
COUNTER, DERIVE, ABSOLUTE, GAUGE. A DS declared as COUNTER will save
the previous value is greater than 0). Traffic counters on a router
are an ideal candidate for using COUNTER as DST. DERIVE is the same as
COUNTER, but it allows negative values as well. If you want to see the
-rate of <em>change</em> in free diskspace on your server, then you might
+rate of <em>change</em> in free disk space on your server, then you might
want to use the DERIVE data type. ABSOLUTE also saves the rate of
change, but it assumes that the previous value is set to 0. The
difference between the current and the previous value is always equal
</p>
<h2><a name="graphical_magic">Graphical Magic</a></h2>
<p>Another important feature of RRDtool is its ability to create
-graphs. The ``graph'' command uses the ``fetch'' command internally to
+graphs. The "graph" command uses the "fetch" command internally to
retrieve values from the database. With the retrieved values it draws
graphs as defined by the parameters supplied on the command line. A
single graph can show different DS (Data Sources) from a database. It
its choice. First it makes sure that the RRA covers as much of the
graphing time frame as possible. Second it looks at the resolution of
the RRA compared to the resolution of the graph. It tries to find one
-which has the same or higher better resolution. With the ``-r'' option
+which has the same or higher better resolution. With the "-r" option
you can force RRDtool to assume a different resolution than the one
calculated from the pixel width of the graph.</p>
<p>Values of different variables can be presented in 5 different shapes
in a graph - AREA, LINE1, LINE2, LINE3, and STACK. AREA is represented
by a solid colored area with values as the boundary of this
area. LINE1/2/3 (increasing width) are just plain lines representing
-the values. STACK is also an area but it is ``stack''ed on top AREA or
+the values. STACK is also an area but it is "stack"ed on top AREA or
LINE1/2/3. Another important thing to note is that variables are
plotted in the order they are defined in the graph command. Therefore
care must be taken to define STACK only after defining AREA/LINE. It
# calculate the average of the array
my $tot_mem_ave = $tot_mem_sum/($count);
# create the graph
- RRDs::graph ("/images/mem_$count.png", \
- "--title= Memory Usage", \
- "--vertical-label=Memory Consumption (MB)", \
- "--start=$start_time", \
- "--end=$end_time", \
- "--color=BACK#CCCCCC", \
- "--color=CANVAS#CCFFFF", \
- "--color=SHADEB#9999CC", \
- "--height=125", \
- "--upper-limit=656", \
- "--lower-limit=0", \
- "--rigid", \
- "--base=1024", \
- "DEF:tot_mem=target.rrd:mem:AVERAGE", \
- "CDEF:tot_mem_cor=tot_mem,0,671744,LIMIT,UN,0,tot_mem,IF,1024,/",\
- "CDEF:machine_mem=tot_mem,656,+,tot_mem,-",\
- "COMMENT:Memory Consumption between $start_time",\
- "COMMENT: and $end_time ",\
- "HRULE:656#000000:Maximum Available Memory - 656 MB",\
- "AREA:machine_mem#CCFFFF:Memory Unused", \
+ RRDs::graph ("/images/mem_$count.png",
+ "--title= Memory Usage",
+ "--vertical-label=Memory Consumption (MB)",
+ "--start=$start_time",
+ "--end=$end_time",
+ "--color=BACK#CCCCCC",
+ "--color=CANVAS#CCFFFF",
+ "--color=SHADEB#9999CC",
+ "--height=125",
+ "--upper-limit=656",
+ "--lower-limit=0",
+ "--rigid",
+ "--base=1024",
+ "DEF:tot_mem=target.rrd:mem:AVERAGE",
+ "CDEF:tot_mem_cor=tot_mem,0,671744,LIMIT,UN,0,tot_mem,IF,1024,/",
+ "CDEF:machine_mem=tot_mem,656,+,tot_mem,-",
+ "COMMENT:Memory Consumption between $start_time",
+ "COMMENT: and $end_time ",
+ "HRULE:656#000000:Maximum Available Memory - 656 MB",
+ "AREA:machine_mem#CCFFFF:Memory Unused",
"AREA:tot_mem_cor#6699CC:Total memory consumed in MB");
my $err=RRDs::error;
if ($err) {print "problem generating the graph: $err\n";}