pmmergelabels(3) — Linux manual page


PMMERGELABELS(3)          Library Functions Manual          PMMERGELABELS(3)

NAME         top

       pmMergeLabels,  pmMergeLabelSets  -  merge sets of performance metric

C SYNOPSIS         top

       #include <pcp/pmapi.h>

       int pmMergeLabels(char **sets, int nsets, char *buffer, int length);

       int pmMergeLabelSets(pmLabelSet **sets, int nsets, char *buffer, int
               length, int (*filter)(const pmLabel *, const char *, void *),
               void *arg);

       cc ... -lpcp


       from pcp import pmapi

       buffer = pmapi.pmContext().pmMergeLabels(sets)
       buffer = pmapi.pmContext().pmMergeLabelSets(sets, filter)

DESCRIPTION         top

       pmMergeLabels takes multiple (nsets) performance metric label sets
       and merges them into a single result buffer of length bytes.  Both
       the input sets and the result buffer are name:value pairs in the
       "JSONB" format described on pmLookupLabels(3).

       The pmMergeLabelSets interface serves the same purpose, but allows
       for indexed sets of labels to be merged.  The format of the
       pmLabelSet data structure is described in detail in

       Although names may repeat across the provided label sets, duplicate
       names are not allowed in the final buffer.  Any label names occuring
       in more than one of the input label sets are reduced to one using the
       rules described in the "PRECEDENCE" section of pmLookupLabels.  The
       position of each element in the sets array is significant in terms of
       the precedence rules - earlier positions are taken to be of lower
       precedence to later positions.

       Values must be primitive JSON entities (e.g. numbers, strings), one-
       dimensional arrays or maps (i.e. simple associative arrays).

       In addition to using indexed label sets the pmMergeLabelSets
       interface provides an optional filter callback function.  If non-
       NULL, this function will be called for each label that would be added
       to the output buffer, allowing finer-grained control over the final
       merged set.  This mechanism can be used to filter individual labels
       based on their name, value, and/or flags.  If the filter function
       returns zero (false), then the given label is filtered from the
       resulting set.  Any non-zero return value indicates that the label
       should be included in the buffer.

PYTHON EXAMPLE         top

       import sys
       import json
       from pcp import pmapi
       import cpmapi as c_api

       def merge_callback(label, jsondata, data=None):
           d = json.loads(jsondata)
           return 0

       ctx = pmapi.pmContext()

       for metric in sys.argv[1:]:
           pmid = ctx.pmLookupName(metric)[0]
           lset = ctx.pmLookupLabels(pmid)
           labelsD = {}
           ctx.pmMergeLabelSets(lset, merge_callback)
           print("== %s ===" % metric)
           for n,v in labelsD.items():
               print("    %s = %s" % (n,v))

DIAGNOSTICS         top

       On success, both pmMergeLabels and pmMergeLabelSets returns the
       number of bytes written into the supplied buffer.

       Failure to parse the input strings, failure to allocate memory, or
       any internal inconsistencies found will result in a negative return

SEE ALSO         top

       pminfo(1), PMAPI(3) and pmLookupLabels(3).

COLOPHON         top

       This page is part of the PCP (Performance Co-Pilot) project.
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Performance Co-Pilot                 PCP                    PMMERGELABELS(3)