path: root/man/man3/pcpintro.3

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.TH PCPINTRO 3 "PCP" "Performance Co-Pilot"
.SH NAME
\f3PCPIntro\f1 \- introduction to the Performance Co-Pilot (PCP) libraries
.SH INTRODUCTION
Performance Co-Pilot (PCP) is a toolkit designed for monitoring
and managing system-level performance.
.PP
The PCP libraries support the APIs required to create new performance
monitoring tools and new agents (or PMDAs) to export performance data.
The
.B libpcp
library is used in both cases.  The
.B libpcp_pmda
library is used only for PMDAs.
.PP
Individual library routines are documented in their own manual page entries.
.PP
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
.BR <pcp/pmapi.h> .
Other negative values are used to encode errors that can be mapped to
the traditional
.I errno
values defined in
.BR <errno.h> ,
with the value negated.
To translate all PCP error codes into useful messages use
either
.BR pmerr (1)
or
.BR pmErrStr (3);
the latter may also be used to decode the
.I \-errno
cases.
.SH "GENERAL ERRORS"
These common errors may occur in various PCP interactions.
.TP 4n
.B PM_ERR_TIMEOUT
.I "Timeout waiting for a response from PMCD"
.br
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.
.RS
.PP
For client\-\c
.B pmcd
timeouts, refer to
.BR PCPIntro (1)
for environment variables that may be used to modify
the timeout thresholds.
For
.BR pmcd -PMDA
timeouts refer to the
.B \-t
and
.B \-q
options of
.BR pmcd (1)
and the PCP metric
.B pmcd.control.timeout
that can be dynamically changed with
.BR pmstore (1).
.RE
.TP
.B PM_ERR_APPVERSION
.I "Metric not supported by this version of monitored application"
.br
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
.BR pmFetch (3)
to indicate these situations.
.TP
.B PM_ERR_IPC
.I "IPC protocol failure"
.br
Generic protocol failure
on a pipe or socket connecting two PCP applications, eg. client\-\c
.BR pmcd ,
or client\-\c
.BR pmtime ,
or PMDA\-\c
.B pmcd
or
.BR pmlc \- pmlogger .
.TP
.B PM_ERR_TEXT
.I "Oneline or help text is not available"
.br
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.
.TP
.B PM_ERR_VALUE
.I "Missing metric value(s)"
.br
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.
.RS
.IP (a) 4n
Bad value for the metric
.B pmcd.timezone
when trying to set the timezone via
.BR pmNewContextZone (3)
for a remote or archive context.
.IP (b)
Attempting to interpolate values for a metric with non-numeric data
type from a PCP archive.
.IP (c)
A bad
.I result
data structure passed to
.BR pmStore (3).
.RE
.TP
.B PM_ERR_NAME
.I "Unknown metric name"
.br
Just what the message says.
.TP
.B PM_ERR_PMID
.I "Unknown or illegal metric identifier"
.br
Just what the message says.
.TP
.B PM_ERR_INDOM
.I "Unknown or illegal instance domain identifier"
.br
A request nominates an instance domain that is unknown
or
.BR PM_INDOM_NULL .
May occur as a consequence of
the instance domain identifier passed by a PCP client to
.BR pmGetInDom (3),
.BR pmLookupInDom (3),
.BR pmNameInDom (3),
.BR pmGetInDomArchive (3),
.BR pmLookupInDomArchive (3),
.BR pmNameInDomArchive (3)
or a request passed from
.BR pmcd (1)
to a PMDA.
.TP
.B PM_ERR_EOF
.I "IPC channel closed"
.br
End of file on a pipe or socket connecting two PCP applications, eg. client\-\c
.BR pmcd ,
or client\-\c
.B pmtime
or PMDA\-\c
.BR pmcd.
.TP
.B PM_ERR_NOCONTEXT
.I "Attempt to use an illegal context"
.br
Typically caused by a PCP client that tries to make calls before
calling
.BR pmNewContext (3)
or after calling
.BR pmDestroyContext (3).
.TP
.B PM_ERR_PERMISSION
.I "No permission to perform requested operation"
.br
PCP-specific access controls apply to
.BR pmcd (1)
and
.BR pmlogger (1).
Platform-specific permission errors are returned as
.BR \-EPERM .
.TP
.B PM_ERR_CONV
.I "Impossible value or scale conversion"
.br
Some value conversion requests are illegal, eg. bad debug flag symbolic name
for
.B \-D
option, or asking
.BR pmExtractValue (3)
to translate non-numeric data types to numbers and
.IR vice " " versa .
.TP
.B PM_ERR_TRUNC
.I "Truncation in value conversion"
.br
Some conversion requests to
.BR pmExtractValue (3)
cannot be performed based on the metric types and values involved,
in this case conversion would result in loss of precision.
.TP
.B PM_ERR_SIGN
.I "Negative value in conversion to unsigned"
.br
Some conversion requests to
.BR pmExtractValue (3)
cannot be performed based on the metric types and values involved,
in this case converting a negative value to an unsigned value.
.TP
.B PM_ERR_TYPE
.I "Unknown or illegal metric type"
.br
The metric type is held in the metric descriptor and sometimes
encoded in the metric values returned from a call to
.BR pmFetch (3).
Legal values for the metric type are defined by the
.B PM_TYPE_*
macros in
.BR <pcp/pmapi.h> .
.TP
.B PM_ERR_UNIT
.I "Illegal pmUnits specification"
.br
Some conversion requests to
.BR pmConvScale (3)
cannot be performed due to illegal or incompatible specifications
of the source and destination units.
.TP
.B PM_ERR_PROFILE
.I "Explicit instance identifier(s) required"
.br
Some PMDAs, especially the
.B proc
PMDA, will not return ``all instances'' for a
.BR pmFetch (3)
request due to the cost.  The client must explicitly built an instance
profile using
.BR pmAddProfile (3)
and/or
.BR pmDelProfile (3)
before calling
.BR pmFetch (3).
See also the
.B \-F
option to
.BR pminfo (1).
.TP
.B PM_ERR_INST
.I "Unknown or illegal instance identifier"
.br
A request to a PMDA nominates an instance that is unknown.
May occur as a consequence of the profile established prior
to a
.BR pmFetch (3)
call, or an explicit instance name or identifier to
.BR pmLookupInDom (3)
or
.BR pmNameInDom (3).
.TP
.B PM_ERR_MODE
.I "Illegal mode specification"
.br
Illegal
.I mode
argument to
.BR pmSetMode (3).
.TP
.B PM_ERR_PROFILESPEC
.I "NULL pmInDom with non-NULL instlist"
.br
Bad arguments passed from a PCP client to
.BR pmAddProfile (3).
.TP
.B PM_ERR_TOOSMALL
.I "Insufficient elements in list"
.br
Parameter passing error by caller specifying a list with less than
one element to
.BR pmFetch (3),
.BR pmLookupName (3)
or
.BR pmStore (3).
.TP
.B PM_ERR_THREAD
.I "Operation not supported for multi-threaded applications"
.br
As documented in
.BR PMAPI (3)
and elsewhere, some
.B libpcp
routines are intended solely for use from single-threaded applications.
.TP
.B PM_ERR_TOOBIG
.I "Result size exceeded"
.br
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.
.TP
.B PM_ERR_RESET
.I "PMCD reset or configuration change"
.br
Not used.
.RS
.PP
Refer to
.BR pmFetch (3)
for an alternative mechanism that may be used to notify
a PCP client when
.BR 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
.B pmcd
and/or changes to the PMDAs under
.BR pmcd 's
control.
.RE
.TP
.B PM_ERR_FAULT
.I "QA fault injected"
.br
Used only for PCP Quality Assurance (QA) testing.
.TP
.B PM_ERR_NYI
.I "Functionality not yet implemented"
.br
Self explanatory and rarely used.
.TP
.B PM_ERR_GENERIC
.I "Generic error, already reported above"
.br
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.
.SH "CLIENT-PMCD ERRORS"
These errors may occur in the interactions between a PCP client and
.BR pmcd (1)
providing real-time performance data.
.TP
.B PM_ERR_NOAGENT
.I "No PMCD agent for domain of request"
.br
A request sent to
.BR 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.
.TP
.B PM_ERR_CONNLIMIT
.I "PMCD connection limit for this host exceeded"
.br
The client connection limit for
.BR pmcd (1)
is controlled by the optional
.B access
controls in
.IR $PCP_PMCDCONF_PATH .
By default there is no limit imposed by the PCP code, and this
error would not be seen.
.TP
.B PM_ERR_AGAIN
.I "Try again. Information not currently available"
.br
Used to notify a PCP client that
the PMDA responsible for delivering the information is temporarily
unavailable.
See also
.BR PM_ERR_PMDANOTREADY .
.TP
.B PM_ERR_NOPROFILE
.I "Missing profile - protocol botch"
.br
Internal error in the communication between a client application
and
.BR pmcd (1)
\- should not occur.
.SH "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
.BR pmlogger (1).
.TP
.B PM_ERR_LOGFILE
.I "Missing archive file"
.br
Each PCP archive consists of multiple physical files as described
in
.BR pmlogger (1).
This error occurs when one of the physical files is missing or
cannot be opened for reading.
.TP
.B PM_ERR_EOL
.I "End of PCP archive log"
.br
An attempt is made to read past the end file of the last volume
of a PCP archive, or past the
end of the time window (as specified with a 
.B \-T
option) for a PCP archive.
.TP
.B PM_ERR_NOTHOST
.I "Operation requires context with host source of metrics"
.br
Operations involving help text (ie. \c
.BR pmLookupText (3)
and
.BR pmLookupInDomText (3))
or calls to
.BR pmStore (3)
require a host context and are not supported for PCP archives.
.TP
.B PM_ERR_LOGREC
.I "Corrupted record in a PCP archive log"
.br
PCP archives can become corrupted for a variety of reasons,
but the most common is premature termination of
.BR pmlogger (1)
without flushing its output buffers.
.TP
.B PM_ERR_LABEL
.I "Illegal label record at start of a PCP archive log file"
.br
Each physical file in a PCP archive should begin with a common
label record.  This is a special case of
.B PM_ERR_LOGREC
errors.
.TP
.B PM_ERR_NODATA
.I "Empty archive log file"
.br
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
.B PM_ERR_LOGREC
errors.
.TP
.B PM_ERR_NOTARCHIVE
.I "Operation requires context with archive source of metrics"
.br
A call to one of the archive variant routines, i.e. \c
.BR pmFetchArchive (3),
.BR pmGetInDomArchive (3),
.BR pmLookupInDomArchive (3)
or
.BR pmNameInDomArchive (3),
when the current context is not associated with a PCP archive.
.TP
.B PM_ERR_PMID_LOG
.I "Metric not defined in the PCP archive log"
.br
A PCP client has requested information about a metric,
and there is no corresponding information in the PCP archive.
This should not happen for well-behaved PCP clients.
.TP
.B PM_ERR_INDOM_LOG
.I "Instance domain identifier not defined in the PCP archive log"
.br
A PCP client has requested information about an instance domain
for one or more performance metrics,
and there is no corresponding information in the PCP archive.
If the client is using metric descriptors from the archive
to identify the instance domain, this is less likely to happen.
.RS
.PP
Because instance domains may vary over time, clients may
need to use the variant routines
.BR pmGetInDomArchive (3)
or
.BR pmLookupInDomArchive (3)
or
.BR pmNameInDomArchive (3)
to manipulate the union of the instances in an instance domain over the life
of an archive.
.RE
.TP
.B PM_ERR_INST_LOG
.I "Instance identifier not defined in the PCP archive log"
.br
A PCP client has requested information about a specific instance
of a performance metric,
and there is no corresponding information in the PCP archive.
If the client is using instance names from the instance
domain in the archive
(rather than hard-coded instance names) and instance identifiers
from the results returned by
.BR pmFetch (3)
or
.BR pmFetchArchive (3)
this is less likely to happen.
.RS
.PP
Because instance domains may vary over time, clients may
need to use the variant routines
.BR pmLookupInDomArchive (3)
or
.BR pmNameInDomArchive (3)
to manipulate the union of the instances in an instance domain over the life
of an archive.
.RE
.SH "TIME CONTROL ERRORS"
These errors may occur in the interactions between a GUI PCP client and
the time control services provided by
.BR pmtime (1).
.TP
.B PM_ERR_ISCONN
.I "Already Connected"
.br
A PCP client application called
.BR pmTimeConnect (3)
when already connected to a
.BR pmtime (1)
instance.
.TP
.B PM_ERR_NOTCONN
.I "Not Connected"
.br
A PCP client application called one of the time control routines
.BR pmTime* (3)
when not currently connected to any
.BR pmtime (1)
instance.
.TP
.B PM_ERR_NEEDPORT
.I "A non-null port name is required"
.br
If a shared
.BR pmtime (1)
instance is being created
the
.I port
argument to
.BR pmTimeConnect (3)
must not be invalid.
.SH "NAMESPACE ERRORS"
These errors may occur in the processing of PCP namespace operations.
A PCP namespace, see
.BR pmns (5),
provides the external
names and the internal identifiers for the available performance metrics.
.TP
.B PM_ERR_NONLEAF
.I "Metric name is not a leaf in PMNS"
.br
The metric name passed to
.BR pmLookupName (3)
names a non-terminal path in the namespace, i.e. a group of metrics
rather than a single metric.
.TP
.B PM_ERR_DUPPMNS
.I "Attempt to reload the PMNS"
.br
When using an explicit local namespace, it is illegal to call
either of
.BR pmLoadNameSpace (3)
or
.BR pmLoadASCIINameSpace (3)
more than once.
.TP
.B PM_ERR_PMNS
.I "Problems parsing PMNS definitions"
.br
Only occurs when an ASCII namespace is explicitly loaded.
.TP
.B PM_ERR_NOPMNS
.I "PMNS not accessible"
.br
Only occurs when an ASCII namespace is explicitly loaded.
.SH "PMCD-PMDA ERRORS"
These error codes are used in the interactions between
.BR pmcd (1)
and the PMDAs that provide the performance data.
.TP
.B PM_ERR_PMDANOTREADY
.I "PMDA is not yet ready to respond to requests"
.br
Some PMDAs have long initialization or reset times, and will respond
to
.BR pmcd (1)
with this error if they are busy at the moment.  This error translates
to
.B PM_ERR_AGAIN
for the PCP client who made the request to
.BR pmcd 
which caused the initial request to the PMDA.
At some later time the PMDA will inform
.B pmcd
(see
.BR PM_ERR_PMDAREADY )
that it is now ready to process requests, and client
requests will begin to succeed.
.TP
.B PM_ERR_PMDAREADY
.I "PMDA is now responsive to requests"
.br
Used by PMDAs to asynchronously inform
.BR pmcd (1)
that they are now willing to resume processing requests.
See also
.BR PM_ERR_PMDANOTREADY .
.SH "PCP ENVIRONMENT"
Environment variables with the prefix
.B PCP_
are used to parameterize the file and directory names
used by PCP.
On each installation, the file
.I /etc/pcp.conf
contains the local values for these variables.
The
.B $PCP_CONF
variable may be used to specify an alternative
configuration file,
as described in
.BR pcp.conf (5).
Values for these variables may be obtained programmatically
using the
.BR pmGetConfig (3)
function.
.SH SEE ALSO
.BR pmerr (1),
.BR PMAPI (3),
.BR pmErrStr (3),
.BR pmGetConfig (3),
.BR pcp.conf (5)
and
.BR pcp.env (5).