pmlogreduce - Online in the Cloud

PROGRAM:

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(7).

-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.

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