Ubuntu Manpage: PCPIntro - introduction to the Performance Co-Pilot (PCP) libraries

NAME

       PCPIntro - introduction to the Performance Co-Pilot (PCP) libraries

INTRODUCTION

       Performance Co-Pilot (PCP) is a toolkit designed for monitoring and managing system-level performance.

       The PCP libraries support the APIs required to create new performance monitoring tools and new agents (or
       PMDAs) to export performance data.  The libpcp library is used in both cases.  The libpcp_pmda library is
       used only for PMDAs.

       Individual library routines are documented in their own manual page entries.

       Most  routines  return an integer value; greater than equal to zero for success and less than zero for an
       error.  The error codes have symbolic names defined in <pcp/pmapi.h>.  Other negative values are used  to
       encode  errors  that  can  be mapped to the traditional errno values defined in <errno.h>, with the value
       negated.  To translate all PCP error codes into useful messages use either pmerr(1) or  pmErrStr(3);  the
       latter may also be used to decode the -errno cases.

GENERAL ERRORS

These common errors may occur in various PCP interactions.

PM_ERR_TIMEOUT
Timeout waiting for a response from PMCD
Many interactions between PCP applications involve synchronous message passing, and these are subject
to timeout constraints. These errors are most frequently encountered when using network connections
with slow data rates or long latencies.

For client-pmcd timeouts, refer to PCPIntro(1) for environment variables that may be used to modify
the timeout thresholds. For pmcd-PMDA timeouts refer to the -t and -q options of pmcd(1) and the PCP
metric pmcd.control.timeout that can be dynamically changed with pmstore(1).

PM_ERR_APPVERSION
Metric not supported by this version of monitored application
Some performance metrics are unavailable from specific versions of the associated PMDA, or may be
unavailable because the underlying instrumentation has changed or is not installed or is not enabled.
This error is used in results from pmFetch(3) to indicate these situations.

PM_ERR_IPC
IPC protocol failure
Generic protocol failure on a pipe or socket connecting two PCP applications, eg. client-pmcd, or
client-pmtime, or PMDA-pmcd or pmlc-pmlogger.

PM_ERR_TEXT
Oneline or help text is not available
Set by a PMDA, and passed back to a PCP client, to indicate that the PMDA is unable to supply the
requested metric or instance domain help text.

PM_ERR_VALUE
Missing metric value(s)
This error is used for a number of conditions in which the value of a performance metric is
inappropriate for the context in which it is being used, eg.

(a) Bad value for the metric pmcd.timezone when trying to set the timezone via pmNewContextZone(3)
for a remote or archive context.

(b) Attempting to interpolate values for a metric with non-numeric data type from a set of PCP
archives.

PM_ERR_NAME
Unknown metric name
Just what the message says.

PM_ERR_PMID
Unknown or illegal metric identifier
Just what the message says.

PM_ERR_INDOM
Unknown or illegal instance domain identifier
A request nominates an instance domain that is unknown or PM_INDOM_NULL. May occur as a consequence
of the instance domain identifier passed by a PCP client to pmGetInDom(3), pmLookupInDom(3),
pmNameInDom(3), pmGetInDomArchive(3), pmLookupInDomArchive(3), pmNameInDomArchive(3) or a request
passed from pmcd(1) to a PMDA.

PM_ERR_EOF
IPC channel closed
End of file on a pipe or socket connecting two PCP applications, eg. client-pmcd, or client-pmtime or
PMDA-pmcd.

PM_ERR_NOCONTEXT
Attempt to use an illegal context
Typically caused by a PCP client that tries to make calls before calling pmNewContext(3) or after
calling pmDestroyContext(3).

PM_ERR_PERMISSION
No permission to perform requested operation
PCP-specific access controls apply to pmcd(1) and pmlogger(1). Platform-specific permission errors
are returned as -EPERM.

PM_ERR_CONV
Impossible value or scale conversion
Some value conversion requests are illegal, eg. bad debug flag symbolic name for -D/--debug option,
or asking pmExtractValue(3) to translate non-numeric data types to numbers and vice versa.

PM_ERR_TRUNC
Truncation in value conversion
Some conversion requests to pmExtractValue(3) cannot be performed based on the metric types and
values involved, in this case conversion would result in loss of precision.

PM_ERR_SIGN
Negative value in conversion to unsigned
Some conversion requests to pmExtractValue(3) cannot be performed based on the metric types and
values involved, in this case converting a negative value to an unsigned value.

PM_ERR_TYPE
Unknown or illegal metric type
The metric type is held in the metric descriptor and sometimes encoded in the metric values returned
from a call to pmFetch(3). Legal values for the metric type are defined by the PM_TYPE_* macros in
<pcp/pmapi.h>.

PM_ERR_UNIT
Illegal pmUnits specification
Some conversion requests to pmConvScale(3) cannot be performed due to illegal or incompatible
specifications of the source and destination units.

PM_ERR_PROFILE
Explicit instance identifier(s) required
Some PMDAs, especially the proc PMDA, will not return ``all instances'' for a pmFetch(3) request due
to the cost. The client must explicitly built an instance profile using pmAddProfile(3) and/or
pmDelProfile(3) before calling pmFetch(3). See also the -F/--fetchall option to pminfo(1).

PM_ERR_INST
Unknown or illegal instance identifier
A request to a PMDA nominates an instance that is unknown. May occur as a consequence of the profile
established prior to a pmFetch(3) call, or an explicit instance name or identifier to
pmLookupInDom(3) or pmNameInDom(3).

PM_ERR_MODE
Illegal mode specification
Illegal mode argument to pmSetMode(3).

PM_ERR_PROFILESPEC
NULL pmInDom with non-NULL instlist
Bad arguments passed from a PCP client to pmAddProfile(3).

PM_ERR_TOOSMALL
Insufficient elements in list
Parameter passing error by caller specifying a list with less than one element to pmFetch(3),
pmLookupName(3) or pmStore(3).

PM_ERR_THREAD
Operation not supported for multi-threaded applications
As documented in PMAPI(3) and elsewhere, some libpcp routines are intended solely for use from
single-threaded applications.

PM_ERR_TOOBIG
Result size exceeded
Indicates a fatal error in the message (or PDU) passing protocol between two PCP applications. This
is an internal error, and other than an exotic networking failure, should not occur.

PM_ERR_RESET
PMCD reset or configuration change
Not used.

Refer to pmFetch(3) for an alternative mechanism that may be used to notify a PCP client when pmcd(1)
has experienced one or more configuration changes since the last request from the client. Usually
these changes involve a change to the namespace exported via pmcd and/or changes to the PMDAs under
pmcd's control.

PM_ERR_FAULT
QA fault injected
Used only for PCP Quality Assurance (QA) testing.

PM_ERR_NYI
Functionality not yet implemented
Self explanatory and rarely used.

PM_ERR_GENERIC
Generic error, already reported above
Rarely used, this error may be returned when the error condition is a consequent of some earlier
returned error and a more precise characterization is not possible.

CLIENT-PMCD ERRORS

       These  errors  may  occur  in  the  interactions  between  a  PCP  client and pmcd(1) providing real-time
       performance data.

       PM_ERR_NOAGENT
              No PMCD agent for domain of request
              A request sent to pmcd(1) requires information from an agent or PMDA that does not exist.  Usually
              this  means  the  namespace  being  used  by  the  client application contains metric names from a
              previously installed PMDA.

       PM_ERR_CONNLIMIT
              PMCD connection limit for this host exceeded
              The client connection limit  for  pmcd(1)  is  controlled  by  the  optional  access  controls  in
              $PCP_PMCDCONF_PATH.   By  default  there is no limit imposed by the PCP code, and this error would
              not be seen.

       PM_ERR_AGAIN
              Try again. Information not currently available
              Used to notify a  PCP  client  that  the  PMDA  responsible  for  delivering  the  information  is
              temporarily unavailable.  See also PM_ERR_PMDANOTREADY.

       PM_ERR_NOPROFILE
              Missing profile - protocol botch
              Internal error in the communication between a client application and pmcd(1) - should not occur.

CLIENT-ARCHIVE ERRORS

       These  errors  may  occur  in the interactions between a PCP client and the library routines that provide
       historical performance data from PCP archives created by pmlogger(1).

       PM_ERR_LOGFILE
              Missing archive file
              Each PCP archive consists of multiple physical files as  described  in  pmlogger(1).   This  error
              occurs when one of the physical files is missing or cannot be opened for reading.

       PM_ERR_EOL
              End of PCP archive log
              An  attempt is made to read past the end file of the last volume of a set of PCP archives, or past
              the end of the time window (as specified with a -T/--finish option) for a set of PCP archives.

       PM_ERR_NOTHOST
              Operation requires context with host source of metrics
              Calls to pmStore(3) require a host context and are not supported for PCP archives.

              For  archives  created  with  versions  of   PCP   prior   to   4.0,   the   pmLookupText(3)   and
              pmLookupInDomText(3)  calls  will  return  this code for archive PMAPI contexts (help and one-line
              text was not previously recorded in archive logs).

       PM_ERR_LOGREC
              Corrupted record in a PCP archive log
              PCP archives can become corrupted for a variety of reasons,  but  the  most  common  is  premature
              termination of pmlogger(1) without flushing its output buffers.

       PM_ERR_LABEL
              Illegal label record at start of a PCP archive log file
              Each  physical  file  in a PCP archive should begin with a common label record.  This is a special
              case of PM_ERR_LOGREC errors.

       PM_ERR_NODATA
              Empty archive log file
              An empty physical file can never be part of a valid PCP archive (at least the label record  should
              be present).  This is a special case of PM_ERR_LOGREC errors.

       PM_ERR_NOTARCHIVE
              Operation requires context with archive source of metrics
              A  call  to  one  of  the  archive variant routines, i.e. pmFetchArchive(3), pmGetInDomArchive(3),
              pmLookupInDomArchive(3) or pmNameInDomArchive(3), when the current context is not associated  with
              a set of PCP archives.

       PM_ERR_PMID_LOG
              Metric not defined in the PCP archive log
              A  PCP  client has requested information about a metric, and there is no corresponding information
              in the set of PCP archives.  This should not happen for well-behaved PCP clients.

       PM_ERR_INDOM_LOG
              Instance domain identifier not defined in the PCP archive log
              A PCP client has requested information about an  instance  domain  for  one  or  more  performance
              metrics,  and  there is no corresponding information in the set of PCP archives.  If the client is
              using metric descriptors from the set of archives to identify the instance domain,  this  is  less
              likely to happen.

              Because  instance  domains  may  vary  over  time,  clients  may  need to use the variant routines
              pmGetInDomArchive(3) or pmLookupInDomArchive(3) or pmNameInDomArchive(3) to manipulate  the  union
              of the instances in an instance domain over the life of an archive.

       PM_ERR_INST_LOG
              Instance identifier not defined in the PCP archive log
              A  PCP  client  has  requested  information about a specific instance of a performance metric, and
              there is no corresponding information in the set of PCP archives.  If the client is using instance
              names  from the instance domain in the set of archives (rather than hard-coded instance names) and
              instance identifiers from the results returned by pmFetch(3) or  pmFetchArchive(3)  this  is  less
              likely to happen.

              Because  instance  domains  may  vary  over  time,  clients  may  need to use the variant routines
              pmLookupInDomArchive(3) or pmNameInDomArchive(3) to manipulate the union of the  instances  in  an
              instance domain over the life of an archive.

       PM_ERR_LOGOVERLAP
              Archives overlap in time
              When using a context associated with a set of archives, the archives in the set may not overlap in
              time.

       PM_ERR_LOGHOST
              Archives differ by host
              When using a context associated with a set of archives, the archives in the set must all have been
              generated on the same host.

       PM_ERR_LOGTIMEZONE
              Archives differ by time zone
              When using a context associated with a set of archives, the archives in the set must all have been
              generated using the same time zone.

       PM_ERR_LOGCHANGETYPE
              The type of a metric differs among archives
              When using a context associated with a set of archives, the type of each metric must  be  same  in
              all of the archives.

       PM_ERR_LOGCHANGESEM
              The semantics of a metric differs among archives
              When  using a context associated with a set of archives, the semantics of each metric must be same
              in all of the archives.

       PM_ERR_LOGCHANGEINDOM
              The instance domain of a metric differs among archives
              When using a context associated with a set of archives, the instance domain of each metric must be
              same in all of the archives.

       PM_ERR_LOGCHANGEUNITS
              The units of a metric differs among archives
              When  using  a context associated with a set of archives, the units of each metric must be same in
              all of the archives.

TIME CONTROL ERRORS

       These errors may occur in the interactions between a  GUI  PCP  client  and  the  time  control  services
       provided by pmtime(1).

       PM_ERR_ISCONN
              Already Connected
              A PCP client application called pmTimeConnect(3) when already connected to a pmtime(1) instance.

       PM_ERR_NOTCONN
              Not Connected
              A  PCP  client  application  called one of the time control routines pmTime*(3) when not currently
              connected to any pmtime(1) instance.

       PM_ERR_NEEDPORT
              A non-null port name is required
              If a shared pmtime(1) instance is being created the port argument to pmTimeConnect(3) must not  be
              invalid.

NAMESPACE ERRORS

       These  errors  may  occur  in  the processing of PCP namespace operations.  A PCP namespace, see PMNS(5),
       provides the external names and the internal identifiers for the available performance metrics.

       PM_ERR_NONLEAF
              Metric name is not a leaf in PMNS
              The metric name passed to pmLookupName(3) names a non-terminal path in the namespace, i.e. a group
              of metrics rather than a single metric.

       PM_ERR_DUPPMNS
              Attempt to reload the PMNS
              When  using  an  explicit  local  namespace, it is illegal to call either of pmLoadNameSpace(3) or
              pmLoadASCIINameSpace(3) more than once.

       PM_ERR_PMNS
              Problems parsing PMNS definitions
              Only occurs when an ASCII namespace is explicitly loaded.

       PM_ERR_NOPMNS
              PMNS not accessible
              Only occurs when an ASCII namespace is explicitly loaded.

PMCD-PMDA ERRORS

       These error codes are used in the interactions between pmcd(1) and the PMDAs that provide the performance
       data.

       PM_ERR_PMDANOTREADY
              PMDA is not yet ready to respond to requests
              Some PMDAs have long initialization or reset times, and will respond to pmcd(1) with this error if
              they are busy at the moment.  This error translates to PM_ERR_AGAIN for the PCP  client  who  made
              the  request  to  pmcd  which caused the initial request to the PMDA.  At some later time the PMDA
              will inform pmcd (see PM_ERR_PMDAREADY) that it is now  ready  to  process  requests,  and  client
              requests will begin to succeed.

       PM_ERR_PMDAREADY
              PMDA is now responsive to requests
              Used  by  PMDAs  to  asynchronously  inform pmcd(1) that they are now willing to resume processing
              requests.  See also PM_ERR_PMDANOTREADY.

PCP ENVIRONMENT

       Environment variables with the prefix PCP_ are used to parameterize the file and directory names used  by
       PCP.   On  each  installation, the file /etc/pcp.conf contains the local values for these variables.  The
       $PCP_CONF variable may be used to specify an alternative configuration file, as described in pcp.conf(5).
       Values for these variables may be obtained programmatically using the pmGetConfig(3) function.