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)