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.
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
This page is part of the PCP (Performance Co-Pilot) project.
Information about the project can be found at ⟨http://www.pcp.io/⟩.
If you have a bug report for this manual page, send it to
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2020-06-09. (At that time, the date of the most recent commit that
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corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
Performance Co-Pilot PCP PMMERGELABELS(3)