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 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 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 consecutive
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 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.
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 configuration
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 sometimes 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.