Provided by: libpcp3-dev_3.8.12ubuntu1_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.
CONTEXT CREATION: pmNewContext
To create a new web context identifier, a web client invokes:
/pmapi/context?local=ANYTHING
Creates a PM_CONTEXT_LOCAL PMAPI context.
/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.
/pmapi/context?archivefile=ARCHIVE
Creates a PM_CONTEXT_ARCHIVE PMAPI context with the given file name.
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.
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, pmTraversePMNS_r
The general form of the requests is as follows:
/pmapi/NNNNN/_metric
Traverse the entire 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.
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.
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
/pmapi/NNNN/_profile_reset?
These are not currently supported.
/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.
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.
SEE ALSO
PCPIntro(1), PCPIntro(3), pmwebd(3), and PMAPI(3)