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PMLOGREDUCE(1)									   PMLOGREDUCE(1)

NAME
       pmlogreduce - temporal reduction of Performance Co-Pilot archives

SYNOPSIS
       $PCP_BINADM_DIR/pmlogreduce  [-z]  [-A align] [-S starttime] [-s samples] [-T endtime] [-t
       interval] [-v volsamples] [-Z timezone] input output

DESCRIPTION
       pmlogreduce reads one Performance Co-Pilot (PCP) archive identified by input (this must be
       a  PCP  archive	created by pmlogger(1), pmlogextract(1) or pmlogreduce(1)), and creates a
       temporally reduced PCP archive in output.  The data  reduction  involves  statistical  and
       temporal reduction of samples with an output sampling interval defined by the -t option in
       the output archive (independent of the sampling intervals in the input  archive),  and  is
       further controlled by other command line arguments.

       For  some metrics, temporal data reduction is not going to be helpful, so for metrics with
       types PM_TYPE_AGGREGATE or PM_TYPE_EVENT, a warning is issued if these metrics  are  found
       in input and they will be skipped and not appear in the output archive.

COMMAND LINE OPTIONS
       The command line options for pmlogreduce are as follows:

       -A align
	      Specify a ``natural'' alignment of the output sample times; refer to PCPIntro(1).

       -S starttime
	      Define  the start of a time window to restrict the samples retrieved from the input
	      archive; refer to PCPIntro(1).

       -s samples
	      The argument samples defines the number of samples to be	written  to  output.   If
	      samples  is  0 or -s is not specified, pmlogreduce will sample until the end of the
	      PCP archive, or the end of the time window as  specified	by  -T,  whichever  comes
	      first.  The -s option will override the -T option if it occurs sooner.

       -T endtime
	      Define  the termination of a time window to restrict the samples retrieved from the
	      input archive; refer to PCPIntro(1).

       -v volsamples
	      The output archive is potentially a multi-volume data set, and the -v option causes
	      pmlogreduce to start a new volume after volsamples log records have been written to
	      the output archive.

	      Independent of any -v option, each volume of an archive is limited to no more  than
	      2^31  bytes,  so pmlogreduce will automatically create a new volume for the archive
	      before this limit is reached.

       -t interval
	      Consecutive samples in the output archive will appear with a time delta defined  by
	      interval;  refer	to  PCPIntro(1).  Note the default value is 600 (seconds, i.e. 10
	      minutes).

       -Z timezone
	      Use timezone when displaying the date and time,  or  interpreting  the  -S  and  -T
	      options.	 Timezone is in the format of the environment variable TZ as described in
	      environ(5).

       -z     Use the local timezone of the host from the input archive when displaying the  date
	      and  time,  or interpreting the -S and -T options.  The default is to initially use
	      the timezone of the local host.

DATA REDUCTION
       The statistical and temporal reduction follows the following rules:

       1.  Consecutive records from input are read without interpolation, and at most one  output
	   record  is  written	for  each  interval,  summarizing  the performance data over that
	   period.

       2.  If the semantics of a metric indicates it is instantaneous  or  discrete  then  output
	   value is computed as the arithmetic mean of the observations (if any) over each inter-
	   val.

       3.  If the semantics of a metric indicates it is a counter then the following  transforma-
	   tions are applied:
	   a)  Metrics with 32-bit precision are promoted to 64-bit precision.
	   b)  Any counter wrap (overflow) is noted, and appropriate adjustment made in the value
	       of the metric over each interval.  This will be correct in the case  of	a  single
	       counter	wrap,  but  will  silently  underestimate in the case where more than one
	       counter wrap occurs between consecutive observations in	the  input  archive,  and
	       silently overestimate in the case where a counter is reset occurs between consecu-
	       tive observations in the input archive; unfortunately these situations  cannot  be
	       detected, but are believed to be rare events for the sort of production monitoring
	       environments where pmlogreduce is most likely to be deployed.

       4.  Any changes in instance domains, and indeed all metadata, is preserved.

       5.  Any ``mark'' records in the input archive (as created by pmlogextract(1)) will be pre-
	   served  in  the  output archive, so periods where no data is available are maintained,
	   and data interpolation will not occur across these periods when the output archive  is
	   subsequently processed with PCP applications.

FILES
       For each of the input and output archives, several physical files are used.
       archive.meta
		 metadata (metric descriptions, instance domains, etc.) for the archive log
       archive.0 initial  volume of metrics values (subsequent volumes have suffixes 1, 2, ...) -
		 for input these files may have  been  previously  compressed  with  bzip2(1)  or
		 gzip(1) and thus may have an additional .bz2 or .gz suffix.
       archive.index
		 temporal  index to support rapid random access to the other files in the archive
		 log.

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 config-
       uration file, as described in pcp.conf(5).

SEE ALSO
       PCPIntro(1),   pmdumplog(1),   pmlc(1),	 pmlogextract(1),  pmlogger(1),  pcp.conf(5)  and
       pcp.env(5).

DIAGNOSTICS
       All error conditions detected by pmlogreduce are reported on stderr with textual (if some-
       times terse) explanation.

       Should  the  input  archive be corrupted (this can happen if the pmlogger instance writing
       the archive suddenly dies), then pmlogreduce will detect and report the	position  of  the
       corruption  in the file, and any subsequent information from the input archive will not be
       processed.

       If any error is detected, pmlogreduce will exit with a non-zero status.

CAVEATS
       The preamble metrics (pmcd.pmlogger.archive, pmcd.pmlogger.host, and  pmcd.pmlogger.port),
       which  are  automatically  recorded  by	pmlogger  at the start of the archive, may not be
       present in the archive output by pmlogreduce.  These metrics are only relevant  while  the
       archive is being created, and have no significance once recording has finished.

Performance Co-Pilot			       PCP				   PMLOGREDUCE(1)
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