@@ -68,11 +60,11 @@ and filled with *UNKNOWN* data.
The name of the RRD you want to create. RRD files should end -with the extension .rrd. However, RRDtool will accept any +with the extension .rrd. However, RRDtool will accept any filename.
-
Specifies the time in seconds since 1970-01-01 UTC when the first value should be added to the RRD. RRDtool will not accept any data timed before or at the time specified.
@@ -80,12 +72,12 @@ any data timed before or at the time specified. rrdfetch documentation for other ways to specify time.-
Specifies the base interval in seconds with which data will be fed into the RRD.
-
A single RRD can accept input from several data sources (DS), for example incoming and outgoing traffic on a specific communication line. With the DS configuration option you must define some basic @@ -100,43 +92,53 @@ DERIVE, and ABSOLUTE the format for a data source entry is:
For COMPUTE data sources, the format is:
DS:ds-name:COMPUTE:rpn-expression
In order to decide which data source type to use, review the -definitions that follow. Also consult the section on "HOW TO MEASURE" +definitions that follow. Also consult the section on ``HOW TO MEASURE'' for further insight.
is for things like temperatures or number of people in a room or the -value of a RedHat share.
+is for things like temperatures or number of people in a room or the +value of a RedHat share.is for continuous incrementing counters like the ifInOctets counter in +is for continuous incrementing counters like the ifInOctets counter in a router. The COUNTER data source assumes that the counter never decreases, except when a counter overflows. The update function takes the overflow into account. The counter is stored as a per-second rate. When the counter overflows, RRDtool checks if the overflow happened at the 32bit or 64bit border and acts accordingly by adding -an appropriate value to the result.
+an appropriate value to the result.will store the derivative of the line going from the last to the +will store the derivative of the line going from the last to the current value of the data source. This can be useful for gauges, for example, to measure the rate of people entering or leaving a room. Internally, derive works exactly like COUNTER but without overflow checks. So if your counter does not reset at 32 or 64 bit you -might want to use DERIVE and combine it with a MIN value of 0.
+might want to use DERIVE and combine it with a MIN value of 0. +NOTE on COUNTER vs DERIVE
+by Don Baarda <don.baarda@baesystems.com>
+If you cannot tolerate ever mistaking the occasional counter reset for a -legitimate counter wrap, and would prefer "Unknowns" for all legitimate +legitimate counter wrap, and would prefer ``Unknowns'' for all legitimate counter wraps and resets, always use DERIVE with min=0. Otherwise, using COUNTER with a suitable max will return correct values for all legitimate -counter wraps, mark some counter resets as "Unknown", but can mistake some +counter wraps, mark some counter resets as ``Unknown'', but can mistake some counter resets for a legitimate counter wrap.
+For a 5 minute step and 32-bit counter, the probability of mistaking a counter reset for a legitimate wrap is arguably about 0.8% per 1Mbps of maximum bandwidth. Note that this equates to 80% for 100Mbps interfaces, so @@ -145,28 +147,30 @@ probably preferable. If you are using a 64bit counter, just about any max setting will eliminate the possibility of mistaking a reset for a counter wrap.
is for counters which get reset upon reading. This is used for fast counters +is for counters which get reset upon reading. This is used for fast counters which tend to overflow. So instead of reading them normally you reset them after every read to make sure you have a maximum time available before the next overflow. Another usage is for things you count like number of messages -since the last update.
+since the last update.is for storing the result of a formula applied to other data sources +is for storing the result of a formula applied to other data sources in the RRD. This data source is not supplied a value on update, but rather its Primary Data Points (PDPs) are computed from the PDPs of the data sources according to the rpn-expression that defines the formula. Consolidation functions are then applied normally to the PDPs of the COMPUTE data source (that is the rpn-expression is only applied to generate PDPs). In database software, such data sets are referred -to as "virtual" or "computed" columns.
+to as ``virtual'' or ``computed'' columns.heartbeat defines the maximum number of seconds that may pass between two updates of this data source before the value of the data source is assumed to be *UNKNOWN*.
@@ -203,27 +207,30 @@ the archive. There are several consolidation functions that consolidate primary data points via an aggregate function: AVERAGE, MIN, MAX, LAST.the average of the data points is stored.
+the average of the data points is stored.the smallest of the data points is stored.
+the smallest of the data points is stored.the largest of the data points is stored.
+the largest of the data points is stored.the last data points is used.
+the last data points is used.Note that data aggregation inevitably leads to loss of precision and information. The trick is to pick the aggregate function such that the interesting properties of your data is kept across the aggregation @@ -242,31 +249,30 @@ Obviously, this has to be greater than zero.
In addition to the aggregate functions, there are a set of specialized functions that enable RRDtool to provide data smoothing (via the Holt-Winters forecasting algorithm), confidence bands, and the flagging aberrant behavior in the data source time series:
RRA:HWPREDICT:rows:alpha:beta:seasonal period[:rra-num]
-RRA:MHWPREDICT:rows:alpha:beta:seasonal period[:rra-num]
-RRA:SEASONAL:seasonal period:gamma:rra-num[:smoothing-window=fraction]
-RRA:DEVSEASONAL:seasonal period:gamma:rra-num[:smoothing-window=fraction]
-RRA:DEVPREDICT:rows:rra-num
-RRA:FAILURES:rows:threshold:window length:rra-num
-These RRAs differ from the true consolidation functions in several ways. First, each of the RRAs is updated once for every primary data point. Second, these RRAs are interdependent. To generate real-time confidence @@ -360,22 +366,21 @@ index in the order of RRA creation (that is, the order they app in the create command). The dependent RRA for each RRA requiring the rra-num argument is listed here:
HWPREDICT rra-num is the index of the SEASONAL RRA.
-SEASONAL rra-num is the index of the HWPREDICT RRA.
-DEVPREDICT rra-num is the index of the DEVSEASONAL RRA.
-DEVSEASONAL rra-num is the index of the HWPREDICT RRA.
-FAILURES rra-num is the index of the DEVSEASONAL RRA.
-threshold is the minimum number of violations (observed values outside the confidence bounds) within a window that constitutes a failure. If the FAILURES RRA is implicitly created, the default value is 7.
@@ -392,28 +397,28 @@ default value is 9. It may help you to sort out why all this *UNKNOWN* data is popping up in your databases:RRDtool gets fed samples/updates at arbitrary times. From these it builds Primary -Data Points (PDPs) on every "step" interval. The PDPs are +Data Points (PDPs) on every ``step'' interval. The PDPs are then accumulated into the RRAs.
-The "heartbeat" defines the maximum acceptable interval between -samples/updates. If the interval between samples is less than "heartbeat", +
The ``heartbeat'' defines the maximum acceptable interval between +samples/updates. If the interval between samples is less than ``heartbeat'', then an average rate is calculated and applied for that interval. If -the interval between samples is longer than "heartbeat", then that -entire interval is considered "unknown". Note that there are other -things that can make a sample interval "unknown", such as the rate +the interval between samples is longer than ``heartbeat'', then that +entire interval is considered ``unknown''. Note that there are other +things that can make a sample interval ``unknown'', such as the rate exceeding limits, or a sample that was explicitly marked as unknown.
-The known rates during a PDP's "step" interval are used to calculate -an average rate for that PDP. If the total "unknown" time accounts for -more than half the "step", the entire PDP is marked -as "unknown". This means that a mixture of known and "unknown" sample -times in a single PDP "step" may or may not add up to enough "known" +
The known rates during a PDP's ``step'' interval are used to calculate +an average rate for that PDP. If the total ``unknown'' time accounts for +more than half the ``step'', the entire PDP is marked +as ``unknown''. This means that a mixture of known and ``unknown'' sample +times in a single PDP ``step'' may or may not add up to enough ``known'' time to warrent for a known PDP.
-The "heartbeat" can be short (unusual) or long (typical) relative to -the "step" interval between PDPs. A short "heartbeat" means you +
The ``heartbeat'' can be short (unusual) or long (typical) relative to +the ``step'' interval between PDPs. A short ``heartbeat'' means you require multiple samples per PDP, and if you don't get them mark the -PDP unknown. A long heartbeat can span multiple "steps", which means +PDP unknown. A long heartbeat can span multiple ``steps'', which means it is acceptable to have multiple PDPs calculated from a single -sample. An extreme example of this might be a "step" of 5 minutes and a -"heartbeat" of one day, in which case a single sample every day will +sample. An extreme example of this might be a ``step'' of 5 minutes and a +``heartbeat'' of one day, in which case a single sample every day will result in all the PDPs for that entire day period being set to the same average rate. -- Don Baarda <don.baarda@baesystems.com>
@@ -459,19 +464,20 @@ same average rate. -- Don Baarda <HOW TO MEASURE-Here are a few hints on how to measure:
-
+- Temperature
- +- Temperature
+- -
-Usually you have some type of meter you can read to get the temperature. +Usually you have some type of meter you can read to get the temperature. The temperature is not really connected with a time. The only connection is that the temperature reading happened at a certain time. You can use the GAUGE data source type for this. RRDtool will then record your reading -together with the time.
+together with the time.- Mail Messages
- + +- Mail Messages
+- -
-Assume you have a method to count the number of messages transported by +Assume you have a method to count the number of messages transported by your mailserver in a certain amount of time, giving you data like '5 messages in the last 65 seconds'. If you look at the count of 5 like an ABSOLUTE data type you can simply update the RRD with the number 5 and the @@ -480,24 +486,25 @@ messages per second. If at some later stage you want to know the number of messages transported in a day, you can get the average messages per second from RRDtool for the day in question and multiply this number with the number of seconds in a day. Because all math is run with Doubles, the -precision should be acceptable.
+precision should be acceptable.- It's always a Rate
- + +- It's always a Rate
+- -
-RRDtool stores rates in amount/second for COUNTER, DERIVE and ABSOLUTE +RRDtool stores rates in amount/second for COUNTER, DERIVE and ABSOLUTE data. When you plot the data, you will get on the y axis amount/second which you might be tempted to convert to an absolute amount by multiplying by the delta-time between the points. RRDtool plots continuous data, and as such is not appropriate for plotting -absolute amounts as for example "total bytes" sent and received in a +absolute amounts as for example ``total bytes'' sent and received in a router. What you probably want is plot rates that you can scale to bytes/hour, for example, or plot absolute amounts with another tool that draws bar-plots, where the delta-time is clear on the plot for each point (such that when you read the graph you see for example GB -on the y axis, days on the x axis and one bar for each day).
+on the y axis, days on the x axis and one bar for each day).
@@ -509,7 +516,7 @@ on the y axis, days on the x axis and one bar for each day). RRA:MIN:0.5:12:2400 \ RRA:MAX:0.5:12:2400 \ RRA:AVERAGE:0.5:12:2400
This sets up an RRD called temperature.rrd which accepts one +
This sets up an RRD called temperature.rrd which accepts one temperature value every 300 seconds. If no new data is supplied for more than 600 seconds, the temperature becomes *UNKNOWN*. The minimum acceptable value is -273 and the maximum is 5'000.