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CentOS 7.0 - man page for __pmcontrollog (centos section 3)

PMCONTROLLOG(3) 		     Library Functions Manual			  PMCONTROLLOG(3)

       __pmControlLog - enable, disable or enquire about logging of performance metrics

       #include <pcp/pmapi.h>
       #include <pcp/impl.h>

       int __pmControlLog(int fd, const pmResult *request, int control, int state, int delta,
	       pmResult **status);

       cc ... -lpcp

       __pmControlLog may be used to enable or disable the archive logging for particular perfor-
       mance  metrics,	as identified by the request parameter; see pmFetch(3) for an explanation
       of the pmResult structure.

       The application must have previously issued a call to __pmConnectLogger(3) to establish	a
       control-port  connection  to the pmlogger(1) instance to whom the control request is to be
       directed, and fd (the result from __pmConnectLogger(3)) identifies this connection.

       Within request, only the details of the performance metrics and their associated instances
       will  be  used,	i.e.   the values of the metrics, if any, will be ignored.  request would
       typically be constructed as the result of an earlier call to pmFetch(3).  For metrics with
       a singular value (having an instance domain of PM_INDOM_NULL) the corresponding pmValueSet
       should have the value one in the numval field and PM_IN_NULL as the inst field of the sin-
       gle  pmValue  supplied.	If multiple explicit instances are to be logged, the numval field
       of the pmValueSet should contain the number of instances supplied and the inst  fields  of
       the  pmValue  structures  should contain specific instance identifiers (which may not have
       the reserved value PM_IN_NULL).

       If the numval field within any of the pmValueSet structures in request has a value of  ze-
       ro,  it	indicates that all available instances of the metric should be used.  Enumeration
       of the instance domain is deferred until the logger fetches the metric prior to writing it
       to the log, rather than being performed when the __pmControlLog request is received.  This
       is useful for metrics with instance domains that change over time.   It	is  an	error  to
       specify numval equal to zero if the corresponding metric has a singular value (no instance

       There are several sorts of logging control available, namely mandatory or advisory, as de-
       fined  by  the  control	argument,  and on, off or maybe as defined by the state argument.
       These different types of control may be used to ensure that some performance  metrics  can
       be guaranteed to always be in the log, while others may be dynamically enabled or disabled
       as determined by the level and type of system activity.

       The actual action to be performed is defined by the combination of control  and	state  as
       follows.   If control is PM_LOG_MANDATORY and state is PM_LOG_ON, then logging is enabled.
       If control is PM_LOG_MANDATORY and state is PM_LOG_OFF, then logging is disabled.  If con-
       trol is PM_LOG_MANDATORY and state is PM_LOG_MAYBE, then subsequent advisory controls will
       be honored.  If the logging state prior to the request was  mandatory  (on  or  off),  the
       state is changed to advisory off.  If the logging state was already advisory (either on or
       off), it remains unchanged.  If control is PM_LOG_ADVISORY and the last mandatory  control
       for  the  metric was PM_LOG_MAYBE, then logging is enabled or disabled as specified by the
       state argument, i.e.  PM_LOG_ON or PM_LOG_OFF.  When the arguments state and control spec-
       ify  a  request to change the logging behavior, the argument delta defines the logging in-
       terval in milliseconds to be applied to all metrics and instances identified in request.

       The result argument status returns the current logging state for  each  of  the	nominated
       performance  metrics.   There  is a 1:1 correspondence between the elements of request and
       status.	For metrics in request that have pmValueSets with numval equal to zero, the  cor-
       responding  pmValueSet  in  result will contain a value for each available instance at the
       time of the call.  Each metric value in status will have the current logging state encoded
       in it.  The detailed outcome of the operation for each metric can be determined by compar-
       ing these values to that requested via control, state and delta.

       Macros defined in <pcp/impl.h> may be used to extract the state and logging interval  from
       the  returned metric values.  PMLC_GET_ON returns true if logging is on, or false if it is
       off; PMLC_GET_MAND returns true if logging is mandatory,  or  false  if	it  is	advisory;
       PMLC_GET_INLOG  returns	true if the metric has been logged at least once, or false other-
       wise; PMLC_GET_AVAIL returns true if the metric was available from  its	source	the  last
       time  it was supposed to be logged, or false if it was unavailable; and PMLC_GET_DELTA re-
       turns the current logging interval for the metric (in milliseconds).   PMLC_MAX_DELTA  de-
       fines the greatest delta that can be returned in an encoded metric value.

       As a special case, when control is PM_LOG_ENQUIRE, state and delta are ignored, and status
       returns the current logging state of the nominated performance metrics (this variant makes
       no changes to the logging state).

       If  the	value of the logging interval is 0, either for delta in a request to change state
       to PM_LOG_ON, or encoded in the value returned from PM_LOG_ENQUIRE, then this  corresponds
       to  the	special ``once only'' logging of metrics that appear once in the archive log, and
       are never logged again.

       __pmControlLog returns zero on success.

       This routine is not thread-safe as there is no serialization on the use of the  communica-
       tion  channel  between  the sending of the request and receiving the reply.  It is assumed
       that the caller is single-threaded, which is true for the only current user of  this  rou-
       tine, namely pmlc(1).

       pmlc(1), pmlogger(1), PMAPI(3), pmFetch(3) and __pmConnectLogger(3).

	      The number of metrics in request is less than one.

	      One or more of the pmValueSets in request had numval (the number of instances) less
	      than one.

       EINVAL An invalid combination of control and state was specified, or delta was negative.

Performance Co-Pilot			       PCP				  PMCONTROLLOG(3)

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