RPN expressions in Torrus

In Torrus framework, RPN expressions are the superset of those in RRDtool version 1.0. See the rrdtool graph manual at <http://oss.oetiker.ch/rrdtool/doc/rrdgraph_rpn.en.html>.

New functions added

Data access

In certain context, the values of the datasources can be evaluated into RPN expression.

The general format for data access is following:

  {FUNC@PATH(-OFFSET)}

FUNC@ specifies a special function to be performed on the data being accessed.

For monitor expressions, T@ returns the timestamp of the data source.

For rrd-cdef leaf types and for rrd-multigraph datasource types, the following functions affect the graph shape: AVERAGE@, MIN@, MAX@, and LAST@. They cause the corresponding Consolidation Function being used when creating a graph.

PATH specifies the relative name for the data source. If omitted, the current leaf value is taken. If starts with /, the path is considered as absolute. Path starting with letter denotes the child of the parent subtree. Double dot (../) in the beginning of the path is interpreted as current parent's parent subtree. If PATH starts with a string enclosed in double square brackets ([[ and ]]), the string is interpreted as a NodeID value for referring to the node in the datasource tree.

(OFFSET) determines the time reference, as described in rrdtool fetch manual. In addition, the word LAST refers to the latest data timestamp available.

(OFFSET) is currently supported in Monitor expressions only.


Author

Copyright (c) 2002-2004 Stanislav Sinyagin <ssinyagin@k-open.com>