Provided by: libpcp-pmda-perl_4.0.1-1_amd64 
NAME
PCP::PMDA - Perl extension for Performance Metrics Domain Agents
SYNOPSIS
use PCP::PMDA;
$pmda = PCP::PMDA->new('myname', $MYDOMAIN);
$pmda->connect_pmcd;
$pmda->add_metric($pmid, $type, $indom, $sem, $units, 'name', '', '');
$pmda->add_indom($indom, [0 => 'white', 1 => 'black', ...], '', '');
$pmda->set_fetch(\&fetch_method);
$pmda->set_refresh(\&refresh_method);
$pmda->set_instance(\&instance_method);
$pmda->set_fetch_callback(\&fetch_callback_method);
$pmda->set_store_callback(\&store_callback_method);
$pmda->set_user('pcp');
$pmda->run;
DESCRIPTION
The PCP::PMDA Perl module contains the language bindings for building Performance Metric
Domain Agents (PMDAs) using Perl. Each PMDA exports performance data for one specific
domain, for example the operating system kernel, Cisco routers, a database, an
application, etc.
METHODS
PCP::PMDA->new(name, domain)
PCP::PMDA class constructor. name is a string that becomes the name of the PMDA for
messages and default prefix for the names of external files used by the PMDA. domain
is an integer domain number for the PMDA, usually from the register of domain numbers
found in $PCP_VAR_DIR/pmns/stdpmid.
$pmda->run()
Once all local setup is complete (i.e. instance domains and metrics are registered,
callbacks registered - as discussed below) the PMDA must connect to pmcd(1) to
complete its initialisation and begin answering client requests for its metrics. This
is the role performed by run, and upon invoking it all interaction within the PMDA is
done via callback routines (that is to say, under normal cicrumstances, the run
routine does not return).
The behaviour of the run method is different in the presence of either the
PCP_PERL_PMNS or PCP_PERL_DOMAIN environment variables. These can be used to generate
the namespace or domain number files, which are used as part of the PMDA installation
process.
$pmda->connect_pmcd()
Allows the PMDA to set up the IPC channel to pmcd(1) and complete the credentials
handshake with pmcd(1). If connect_pmcd is not explicitly called the setup and
handshake will be done when the run method is called.
The advantage of explicitly calling connect_pmcd early in the life of the PMDA is that
this reduces the risk of a fatal timeout during the credentials handshake, which may
be an issue if the PMDA has considerable work to do, e.g. determining which metrics
and instance domains are available, before calling run.
$pmda->add_indom(indom, insts, help, longhelp)
Define a new instance domain. The instance domain identifier is indom, which is an
integer and unique across all instance domains for single PMDA.
The instances of the instance domain are defined by insts which can be specified as
either a list or a hash.
In list form, the contents of the list must provide consecutive pairs of identifier (a
integer, unique across all instances in the instance domain) and external instance
name (a string, must by unique up to the first space, if any, across all instances in
the instance domain). For example:
@colours = [0 => 'red', 1 => 'green', 2 => 'blue'];
In hash form, the external instance identifier (string) is used as the hash key. An
arbitrary value can be stored along with the key (this value is often used as a
convenient place to hold the latest value for each metric instance, for example).
%timeslices = ('sec' => 42, 'min' => \&min_func, 'hour' => '0');
The help and longhelp strings are interpreted as the one-line and expanded help text
to be used for this instance domain as further described in pmLookupInDomText(3).
Refer also to the replace_indom() discussion below for further details about
manipulating instance domains.
$pmda->add_metric(pmid, type, indom, sem, units, name, help, longhelp)
Define a new metric identified by the PMID pmid and the full metric name name.
The metric's metadata is defined by type, indom, sem and units and these parameters
are used to set up the pmDesc structure as described in pmLookupDesc(3).
The help and longhelp strings are interpreted as the one-line and expanded help text
to be used for the metric as further described in pmLookupText(3).
$pmda->replace_indom(index, insts)
Whenever an instance domain identified by index, previously registered using
add_indom(), changes in any way, this change must be reflected by replacing the
existing mapping with a new one (insts).
The replacement mapping must be a hash if the instance domain was registered initially
with add_indom() as a hash, otherwise it must be a list.
Refer to the earlier add_indom() discussion concerning these two different types of
instance domains definitions.
$pmda->load_indom(index)
When hash-based instance domains are in use, changes are automatically persisted when
using replace_indom() - this persisted indom can be restored (e.g. on startup) using
this interface.
The instance domain to be loaded is identified by index, previously registered using
add_indom().
Refer to the earlier add_indom() discussion concerning the two different types of
instance domains definitions - only hash-based instance domains are persisted.
$pmda->add_pipe(command, callback, data)
Allow data to be injected into the PMDA using a pipe(2).
The given command is run early in the life of the PMDA, and a pipe is formed between
the PMDA and the command. Line-oriented output is assumed (else truncation will
occur), and on receipt of each line of text on the pipe, the callback function will be
called.
The optional data parameter can be used to specify extra data to pass into the
callback routine.
$pmda->add_sock(hostname, port, callback, data)
Create a socket(2) connection to the hostname, port pair. Whenever data arrives (as
above, a line-oriented protocol is best) the callback function will be called.
The optional data parameter can be used to specify extra data to pass into the
callback routine.
An opaque integer-sized identifier for the socket will be returned, which can later be
used in calls to put_sock() as discussed below.
$pmda->put_sock(id, output)
Write an output string to the socket identified by id, which must refer to a socket
previously registered using add_sock().
$pmda->add_tail(filename, callback, data)
Monitor the given filename for the arrival of newly appended information. Line-
oriented input is assumed (else truncation will occur), and on receipt of each line of
text on the pipe, the callback function will be called.
The optional data parameter can be used to specify extra data to pass into the
callback routine.
This interface deals with the issue of the file being renamed (such as on daily log
file rotation), and will attempt to automatically re-route information from the new
log file if this occurs.
$pmda->add_timer(timeout, callback, data)
Registers a timer with the PMDA, such that on expiry of a timeout a callback routine
will be called. This is a repeating timer.
The optional data parameter can be used to specify extra data to pass into the
callback routine.
$pmda->err(message)
Report a timestamped error message into the PMDA log file.
$pmda->error(message)
Report a timestamped error message into the PMDA log file.
$pmda->log(message)
Report a timestamped informational message into the PMDA log file.
$pmda->set_fetch_callback(cb_function)
Register a callback function akin to pmdaSetFetchCallBack(3).
$pmda->set_fetch(function)
Register a fetch function, as used by pmdaInit(3).
$pmda->set_instance(function)
Register an instance function, as used by pmdaInit(3).
$pmda->set_refresh(function)
Register a refresh function, which will be called once per metric cluster, during the
fetch operation. Only clusters being requested during this fetch will be refreshed,
allowing selective metric value updates within the PMDA.
$pmda->set_store_callback(cb_function)
Register an store function, used indirectly by pmdaInit(3). The cb_function is called
once for each metric/instance pair into which a pmStore(3) is performed.
$pmda->set_inet_socket(port)
Specify the IPv4 socket port to be used to communicate with pmcd(1).
$pmda->set_ipv6_socket(port)
Specify the IPv6 socket port to be used to communicate with pmcd(1).
$pmda->set_unix_socket(socket_name)
Specify the filesystem socket_name path to be used for communication with pmcd(1).
$pmda->set_user(username)
Run the PMDA under the username user account, instead of the default (root) user.
HELPER METHODS
pmda_pmid(cluster, item)
Construct a Performance Metric Identifier (PMID) from the domain number (passed as an
argument to the new constructor), the cluster (an integer in the range 0 to 2^12-1)
and the item (an integer in the range 0 to 2^10-1).
Every performance metric exported from a PMDA must have a unique PMID.
pmda_pmid_name(cluster, item)
Perform a reverse metric identifier to name lookup - given the metric cluster and item
numbers, returns the metric name string.
pmda_pmid_text(cluster, item)
Returns the one-line metric help text string - given the metric cluster and item
numbers, returns the help text string.
pmda_inst_name(index, instance)
Perform a reverse instance identifier to instance name lookup for the instance domain
identified by index. Given the internal instance identifier, returns the external
instance name string.
pmda_inst_lookup(index, instance)
Given an internal instance identifier (key) for the instance domain identified by
index with an associated indom hash, return the value associated with that key. The
value can be any scalar value (this includes references, of course, so complex data
structures can be referenced).
pmda_units(dim_space, dim_time, dim_count, scale_space, scale_time, scale_count)
Construct a pmUnits structure suitable for registering a metrics metadata via
add_metric().
pmda_config(name)
Lookup the value for configuration variable name from the /etc/pcp.conf file, using
pmGetConfig(3).
pmda_uptime(now)
Return a human-readable uptime string, based on now seconds since the epoch.
pmda_long()
Return either PM_TYPE_32 or PM_TYPE_64 depending on the platform size for a signed
long integer.
pmda_ulong()
Return either PM_TYPE_U32 or PM_TYPE_U64 depending on the platform size for an
unsigned long integer.
pmda_install()
Boolean result indicating whether PMDA installation is in progress, or if this is an
actual PMDA invocation via pmcd(1).
MACROS
Most of the PM_* macros from the PCP C headers are available.
For example the type of a metric's value may be directly specified as one of PM_TYPE_32,
PM_TYPE_U32, PM_TYPE_64, PM_TYPE_U64, PM_TYPE_FLOAT, PM_TYPE_DOUBLE, PM_TYPE_STRING or
PM_TYPE_NOSUPPORT.
DEBUGGING
Perl PMDAs do not follow the -D convention of other PCP applications for enabling run-time
diagnostics and tracing. Rather the environment variable PCP_PERL_DEBUG needs to be set
to a string value matching the syntax accepted for the option value for -D elsewhere, see
pmSetDebug(3).
This requires a little trickery. The pmcd(1) configuration file (PCP_PMCDCONF_PATH from
/etc/pcp.conf) needs hand editing. This is best demonstrated by example.
Replace this line
foo 242 pipe binary python /somepath/foo.py
with
foo 242 pipe binary python \
sh -c "PCP_PERL_DEBUG=pdu,fetch /usr/bin/python /somepath/foo.py"
SEE ALSO
perl(1) and PCPIntro(1).
The PCP mailing list pcp@groups.io can be used for questions about this module.
Further details can be found at http://www.pcp.io
AUTHOR
The Performance Co-Pilot development team.
Copyright (C) 2014 Red Hat. Copyright (C) 2008-2010 Aconex. Copyright (C) 2004 Silicon
Graphics, Inc.
This library is free software; you can redistribute it and/or modify it under the terms of
the GNU General Public License, version 2 (see the "COPYING" file in the PCP source tree
for further details).