вернуть описания экземпляров для PMDA (return instance descriptions for a PMDA)
Имя (Name)
pmdaInstance - return instance descriptions for a PMDA
Синопсис C (C Synopsis)
#include <pcp/pmapi.h>
#include <pcp/pmda.h>
int pmdaInstance(pmInDom indom, int inst, char *name,
pmInResult **result, pmdaExt *pmda);
cc ... -lpcp_pmda -lpcp
Описание (Description)
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).
MULTI-DIMENSIONAL INSTANCE NAMING
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.
Предостережение (Caveat)
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.
Диагностика (Diagnostic)
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.
Смотри также (See also)
malloc(3), PMAPI(3), PMDA(3), pmdaCacheStore(3), pmdaLabel(3) and
pmGetInDom(3).
