pmlogreduce reads one set of Performance Co-Pilot (PCP) archives
identified by input and creates a temporally reduced PCP archive in
output. input is a comma-separated list of names, each of which may
be the base name of an archive or the name of a directory containing
one or more archives. 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 archives), 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.
The command line options for pmlogreduce are as follows:
Specify a ``natural'' alignment of the output sample times;
refer to PCPIntro(1).
Define the start of a time window to restrict the samples
retrieved from the input archives; refer to PCPIntro(1).
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 set of PCP
archives, 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.
Define the termination of a time window to restrict the
samples retrieved from the input archives; refer to
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
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.
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).
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(7).
-z Use the local timezone of the host from the input archives
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.
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 interval.
3. If the semantics of a metric indicates it is a counter then the
following transformations are applied:
a) Metrics with 32-bit precision are promoted to 64-bit
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 archives, and silently overestimate
in the case where a counter is reset occurs between
consecutive observations in the input archives; 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
5. Any ``mark'' records in the input archives (as created by
pmlogextract(1)) will be preserved 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.
For each of the input and output archives, several physical files are
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.
temporal index to support rapid random access to the other
files in the archive log.
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).
All error conditions detected by pmlogreduce are reported on stderr
with textual (if sometimes terse) explanation.
Should the input archives 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 archives will
not be processed.
If any error is detected, pmlogreduce will exit with a non-zero
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.
This page is part of the PCP (Performance Co-Pilot) project.
Information about the project can be found at ⟨http://www.pcp.io/⟩.
If you have a bug report for this manual page, send it to
firstname.lastname@example.org. This page was obtained from the project's upstream
Git repository ⟨git://git.pcp.io/pcp⟩ on 2017-03-13. If you discover
any rendering problems in this HTML version of the page, or you
believe there is a better or more up-to-date source for the page, or
you have corrections or improvements to the information in this
COLOPHON (which is not part of the original manual page), send a mail
Performance Co-Pilot PCP PMLOGREDUCE(1)