pmlogreduce — temporal reduction of Performance Co-Pilot archives
$PCP_BINADM_DIR/pmlogreduce [-z?] [-A align] [-s samples] [-S starttime] [-t interval] [-T endtime] [-v volsamples] [-Z timezone] input output
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 available command line options are:
- -A align, --align=align
Specify a “natural” alignment of the output sample times; refer to PCPIntro(1).
- -s samples, --samples=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 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.
- -S starttime, --start=starttime
Define the start of a time window to restrict the samples retrieved from the input archives; refer to PCPIntro(1).
- -t interval, --interval=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).
- -T endtime, --finish=endtime
Define the termination of a time window to restrict the samples retrieved from the input archives; 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.
- -z, --hostzone
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.
- -Z timezone, --timezone=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(7).
- -?, --help
Display usage message and exit.
The statistical and temporal reduction follows the following rules:
- 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.
- 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.
If the semantics of a metric indicates it is a counter then the following transformations are applied:
Metrics with 32-bit precision are promoted to 64-bit precision.
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 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.
- Any changes in instance domains, and indeed all metadata, is preserved.
- 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.
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.
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 status.
For each of the input and output archives, several physical files are used.
metadata (metric descriptions, instance domains, etc.) for the archive log
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).
PCPIntro(1), pmdumplog(1), pmlc(1), pmlogextract(1), pmlogger(1), pcp.conf(5) and pcp.env(5).
LOGARCHIVE(5), pmlogextract(1), pmlogrewrite(1), pmmgr(1).