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NAME | C SYNOPSIS | DESCRIPTION | MULTI-DIMENSIONAL INSTANCE NAMING | DIAGNOSTICS | CAVEAT | SEE ALSO | COLOPHON |
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PMDAINSTANCE(3) Library Functions Manual PMDAINSTANCE(3)
pmdaInstance - return instance descriptions for a PMDA
#include <pcp/pmapi.h>
#include <pcp/pmda.h>
int pmdaInstance(pmInDom indom, int inst, char *name,
pmInResult **result, pmdaExt *pmda);
cc ... -lpcp_pmda -lpcp
pmdaInstance uses the standard PMDA(3) data structures to return
information concerning the instance domain indom.
The result structure is constructed by pmdaInstance and will contain
one or more instance names and/or identifiers as specified by the
inst and name arguments.
If inst has the value PM_IN_NULL and name is a null string, result
will contain all the instances names and identifiers in the instance
domain.
If inst is PM_IN_NULL but name is the name of an instance in the
instance domain indom, then result will contain the instance
identifier for instance name. Note that if name contains no spaces,
partial matching up to the first space in the instance name is
performed, i.e. ``1'' will match instance name ``1 minute''. If
name contains an embedded space, then no partial matching is
performed and name should match one of the instance names exactly.
If name is a null string but inst is an instance identifier in the
instance domain indom, then result will contain the name for instance
inst. The result structure is allocated with malloc(3) and should be
released by the caller with free(3).
Further to the above description of name, the set of rules describing
external instance names is provided in the pmdaCacheStore(3) manual
page.
Instance domains adds another dimension (set of values) to metrics.
However, this may not suffice to describe complex multi-dimensional
instance domain situations. For this case the approach used by a
number of PMDAs is to structure the external instance names using a
delimiter (``/'' or ``::'' are most commonly used) to allow
separation of the other dimensions. In this situation, instance
domain labels should be used to define names for each instance name
component. This allows PMAPI(3) client tools to identify and refine
value fetches to specific dimensions of interest.
For example, some of the Linux kernel cgroup (control group) metric
instance domains are multi-dimensional. The instance domain
represents individual values across both control groups and CPUs,
making this a two-dimensional instance domain. The instance names
associated with this cgroup metrics indom have been structured using
the ``::'' delimiter to separate the two dimensions. The instance
domain itself has been labeled accordingly, as follows.
$ pminfo --desc --fetch --labels cgroup.cpuacct.usage_percpu
cgroup.cpuacct.usage_percpu
Data Type: 64-bit unsigned int InDom: 3.22 0xc00016
Semantics: counter Units: nanosec
inst [0 or "/::cpu0"] value 713787
inst [1 or "/::cpu1"] value 353969
inst [2 or "/app::cpu0"] value 407816
inst [3 or "/app::cpu1"] value 202747
inst [0 or "/::cpu0"] labels {"device_type":"cpu","cgroup":"/","cpu":0}
inst [1 or "/::cpu1"] labels {"device_type":"cpu","cgroup":"/","cpu":1}
inst [2 or "/app::cpu0"] labels {"device_type":"cpu","cgroup":"/app","cpu":0}
inst [3 or "/app::cpu1"] labels {"device_type":"cpu","cgroup":"/app","cpu":1}
$ pminfo --labels 3.22
InDom: 3.22 0xc00016
labels {"device_type":"cpu"}
As shown above the individual instances inherit the labels from the
instance domain, and the PMDA also applies additional per-instance
labels describing individual cgroup and CPU names. When this model
has been used by the PMDA, PMAPI clients are able to restrict their
queries to the cgroup metric instances - in the example, restricting
to processor "cpu0" using the "cpu" label, perhaps, or to just the
"/app" cgroup metrics using the "cgroup" label.
Furthermore, using this labeling scheme client tools can also
correlate related instances across different instance domains.
$ pminfo --desc --fetch --labels kernel.percpu.cpu.irq.soft
kernel.percpu.cpu.irq.soft
Data Type: 64-bit unsigned int InDom: 60.0 0xf000000
Semantics: counter Units: millisec
inst [0 or "cpu0"] value 6770
inst [1 or "cpu1"] value 100
inst [0 or "cpu0"] labels {"device_type":"cpu"}
inst [1 or "cpu1"] labels {"device_type":"cpu"}
$ pminfo --labels 60.0
InDom: 60.0 0xf000000
labels {"device_type":"cpu"}
Although these two metrics have different instance domains (60.0 and
3.22 respectively) and are sourced from different PMDAs, the
"device_type" label identifies the common device to which these
values relate.
If any errors occur during the execution of pmdaInstance, the result
structure is deallocated. If the instance domain indom is not
supported by the PMDA, pmdaInstance will return PM_ERR_INDOM.
If the inst or name does not correspond to any instances in the indom
domain, pmdaInstance will return PM_ERR_INST.
The PMDA must be using PMDA_INTERFACE_2 or later, as specified in the
call to pmdaDSO(3) or pmdaDaemon(3). If labeling of multi-
dimensional instance names is performed, the PMDA must use
PMDA_INTERFACE_7 or later.
Because of optional partial matching up to the first space in the
instance name, the PMDA developer should ensure that if instance
names are allowed to have spaces, the names are unique up to the
first space.
malloc(3), PMAPI(3), PMDA(3), pmdaCacheStore(3), pmdaLabel(3) and
pmGetInDom(3).
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
pcp@groups.io. This page was obtained from the project's upstream
Git repository ⟨https://github.com/performancecopilot/pcp.git⟩ on
2018-02-02. (At that time, the date of the most recent commit that
was found in the repository was 2018-02-02.) If you discover any
rendering problems in this HTML version of the page, or you believe
there is a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
man-pages@man7.org
Performance Co-Pilot PCP PMDAINSTANCE(3)
Pages that refer to this page: pmlogrewrite(1), pmda(3), pmdacache(3), pmdadaemon(3), pmdadso(3), pmdamain(3)
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