Provided by: pcp-webapi_4.0.1-1_amd64 
NAME
PMWEBAPI - introduction to the Performance Metrics Web Application Programming Interface
OVERVIEW
The PMWEBAPI interface is a binding of a subset of the PMAPI to the web. It uses HTTP as transport, REST
as organizational style for request/parameter encoding (the GET and POST methods are interchangeable),
and JSON as response encoding. A context identifier is used as a persistent way to refer to PMAPI
contexts across related web requests. These context identifiers expire after a configurable period of
disuse.
Errors generally result in HTTP-level error responses. An Access-Control-Allow-Origin: * header is added
to all JSON responses.
CONTEXT CREATION: pmNewContext
To create a new web context identifier, a web client invokes:
/pmapi/context?hostname=STRING
/pmapi/context?hostspec=STRING
Creates a PM_CONTEXT_HOST PMAPI context with the given host name and/or extended specification.
If the host specification contains a userid/password combination, then the corresponding PMAPI
context operations will require HTTP Basic authentication credentials with matching
userid/password.
In addition, the web client may add the parameter &polltimeout=MMMM for a maximum interval (in seconds)
between expected accesses to the given context. This value is limited by pmwebd configuration, and is a
courtesy to allow pmwebd to free up memory earlier in case of sudden web application shutdown.
If successful, the response from these requests is a JSON document of the form:
{ "context" : NNNNN }
The number (a 32-bit unsigned decimal) is then used in all later operations.
CONTEXT CREATION: configurable permanent contexts
In addition, permanent contexts may be created by pmwebd at initialization using its -h, -a, -L command
line options, so that a set of fixed NNNNN numbers may be made available to web clients.
PMAPI OPERATIONS
The general form of the requests is as follows: /pmapi/NNNNN/OPERATION where
/pmapi is the fixed prefix for all PMWEBAPI operations,
NNNNN is a PMWEBAPI context number returned from a context-creation call, or assigned permanently at
pmwebd startup, and
OPERATION?PARAM1=VALUE2&PARAM2=VALUE2
identifies the operation and its URL-encoded parameters. Some parameters may be optional.
METRIC METADATA: pmLookupName, pmLookupDesc, pmLookupText, pmTraversePMNS_r
The general form of the requests is as follows:
/pmapi/NNNNN/_metric
Traverse the entire Performance Metrics Name Space (PMNS).
/pmapi/NNNNN/_metric?prefix=NAME
Traverse the subtree of PMNS with the prefix NAME.
The response is a JSON document that provides the metric metadata as an array. For example:
{ "metrics": [
{ "name":"foo.bar", "pmID":PPPP, "indom":DDDD,
"type":"32", "sem":"instant", "units":"MHz",
"text-oneline":"foo bar", "text-help":"blah blah blah" },
{ "name":"foo.bar2", ... }
...
] }
Most of the fields are self-explanatory.
name A name for the metric as defined in the PMNS. If the PMNS contains multiple names associated with
the metric's Performance Metric Identifier (PMID), one of these will be returned via name, but
there is no way to determine which of the duplicate names this will be.
PPPP the PMID
DDDD the instance domain
type from pmTypeStr
units from pmUnitsStr
sem an abbreviation of the metric semantic:
PM_SEM_COUNTER "counter"
PM_SEM_INSTANT "instant"
PM_SEM_DISCRETE "discrete"
METRIC VALUE: pmFetch
The general form of the requests is as follows:
/pmapi/NNNNN/_fetch?names=NAME1,NAME2
Fetch current values for given named metrics.
/pmapi/NNNNN/_fetch?pmids=PPPP1,PPPP2
Fetch current values for given PMIDs.
If any of the names/pmids are valid, the response is a JSON document that provides the values for all
requested metrics, for all their instances.
{ "timestamp": { "s":SEC, "us":USEC },
"values": [
{ "pmid":PPPP1, "name":"NAME1",
"instances:" [
{ "instance":IIII1, "value":VALUE1 }
{ "instance":IIII2, "value":VALUE2 }
...
] },
{ "pmid":PPPP2, "name":"NAME2", ... }
...
] }
Most of the fields are self-explanatory. Numeric metric types are represented as JSON integer or
floating-point values. Strings are passed verbatim, except that non-ASCII values are replaced with a
Unicode 0xFFFD REPLACEMENT CHARACTER code. Event type metrics are not currently supported.
INSTANCE DOMAINS METADATA: pmGetInDom, pmNameInDom, pmLookupInDom
The general form of the requests is as follows:
/pmapi/NNNN/_indom?indom=DDDD
List instances of the given instance domain.
/pmapi/NNNN/_indom?name=NAME
List instances of the instance domain belonging to the named metric.
In addition, either query may be suffixed with:
&instance=IIII,JJJJ
Restrict listings to given instance code numbers.
&iname=INAME1,INAME2
Restrict listings to given instance names.
The response is a JSON document that provides the metric metadata as an array. For example:
{ "indom":DDDD,
"instances": [
{ "instance":IIII, "name":"INAME" }
...
] }
INSTANCE PROFILE: pmAddProfile, pmDelProfile
The general form of these requests is as follows:
/pmapi/NNNN/_profile_reset?indom=DDDD
These are not currently supported.
/pmapi/NNNN/_profile_add?indom=DDDD&instance=IIII,JJJJ
These are not currently supported.
/pmapi/NNNN/_profile_add?indom=DDDD&iname=IIII,JJJJ
These are not currently supported.
/pmapi/NNNN/_profile_del?indom=DDDD&instance=JJJJ
These are not currently supported.
/pmapi/NNNN/_profile_del?indom=DDDD&iname=INAME1,INAME2
These are not currently supported.
METRIC STORE: pmStore
The general form of these requests is as follows:
/pmapi/NNNN/_store?name=NAME&value=VALUE
Store a new value for given named metrics.
/pmapi/NNNNN/_store?pmid=PPPP&value=VALUE
Store a new value for given performance metric identifier (PMID).
In addition, either query may be suffixed with:
&instance=IIII,JJJJ
Restrict store to given instance code numbers.
&iname=INAME1,INAME2
Restrict store to given instance names.
If successful, the response from these requests is a JSON document of the form:
{ "success" : true }
DERIVED METRICS: pmRegisterDerived
/pmapi/NNNNN/_derive?name=NAME&expr=EXPRESSION
These are not currently supported.
CONTEXT COPY: pmDupContext
/pmapi/NNNNN/copy
These are not currently supported.
CONTEXT CLOSE: pmDestroyContext
/pmapi/NNNNN/destroy
This is not likely to be supported, as it is destructive and would offer a tempting target to
brute-force attackers. Instead, the pmwebd timeout is used to automatically free unused contexts.
PROMETHEUS
Prometheus exporting of live metrics from a preexisting PMWEBAPI context is available:
The general form of the requests is:
/pmapi/NNNNN/metrics?target=NAME1,NAME2,...
Fetch current values for given named metrics.
For all numeric metrics with the given NAME prefixes, create a prometheus text export format giving their
current value and related metadata. The response has text/plain type rather than JSON, and is designed
to be ingested by a Prometheus server, or pcp's own pmdaprometheus.
The native PCP metric metadata (metric name, semantics and units) are first output with the # PCP prefix.
If the units string is empty, then none is output. The units metadata string may contain spaces and
extends to the end of the line. Prometheus metric types are heuristically inferred from PCP metric
types, and units/scales are converted to base seconds/bytes/count if possible, with a corresponding
suffix added to the metric name. PCP metric names are mapped so that . are exchanged with :. Instance
domain instances are represented as Prometheus labels with quoted instance names.
# PCP proc.nprocs instant none
# HELP proc:nprocs instantaneous number of processes
# TYPE proc:nprocs gauge
proc:nprocs 7
# PCP kernel.pernode.cpu.intr counter millisec
# HELP kernel:pernode:cpu:intr_seconds_total total interrupt CPU time from /proc/stat for each node
# TYPE kernel:pernode:cpu:intr_seconds_total counter
kernel:pernode:cpu:intr_seconds_total{instance="node0"} 25603.540000000001
# PCP filesys.blocksize instant byte
# HELP filesys:blocksize_bytes Size of each block on mounted filesystem (Bytes)
# TYPE filesys:blocksize_bytes gauge
filesys:blocksize_bytes{instance="/dev/mapper/docker-253:0-83713-\
9a130460b46163fcf4443710db3159dea6bb5ec2aaca108515839a7a28c191ce"} 4096
filesys:blocksize_bytes{instance="/dev/mapper/VolGroup00-root17"} 4096
GRAPHITE
When enabled, pmwebd can emulate a subset of the graphite web-api to allow web applications like graphite
and grafana to extract data from all archives under the configured -A directory. The graphite namespace
is constructed from the PCP archives using a simple mapping that encodes the Cartesian product of
archives, metrics, and instance-domain instances into dot-separated strings. Some metacharacter-quoting
is employed to encode general strings into components. Only numeric PCP metrics are exposed; COUNTER
semantic values are rate-converted.
┌─────────┬────────┬───────────────────────────────────────────────────────┐
│position │ number │ purpose │
├─────────┼────────┼───────────────────────────────────────────────────────┤
│ 1 │ 1 │ encoded pathname of the archive .meta file (default), │
│ │ │ or canonicalized archive hostname (-J mode) │
│ 2 │ N │ the N components of the pcp metric name │
│ N+2 │ 1 │ instance name of the metric (if any) │
└─────────┴────────┴───────────────────────────────────────────────────────┘
Since glob wildcarding is supported within metric name components, using them in the first component (an
encoding of the archive name) is a good way to identify machines, or to match multiple archives spanning
times of interest.
We list here only the broadest outline of the supported calls. pmwebd does not support every graphite
web-api option, so many querystring parameters may be ignored. Arithmetic/statistical functions on
metrics are not supported.
/graphite/render?format=json&target=FOO&from=TIME&until=TIME
Return a series of values of the given metrics, between the two times, sampled every 60 seconds.
/graphite/rawdata?target=FOO.BAR&from=TIME&until=TIME
Same, with a slightly different result encoding.
/graphite/render?format=png&target=FOO&from=TIME&until=TIME&....
Same, but render the curves into a PNG image file. Several color- and rendering-control-related
parameters are supported.
/graphite/metrics/find?query=FOO.BAR.*
Provide incremental metric-tree traversal using wildcards.
/graphite/graphlot/findmetric?query=FOO+BAR
Search through metrics with space-separated regular expressions.
/graphite/browser/search?q=FOO+BAR
Same, with a slightly different result encoding.
SEE ALSO
PCPIntro(1), PCPIntro(3), pmwebd(1), http://graphite.readthedocs.org/ and PMAPI(3)