Chapter 6. Logging performance data with pmlogger

With the PCP tool you can log the performance metric values and replay them later. This allows you to perform a retrospective performance analysis.

Using the pmlogger tool, you can:

  • Create the archived logs of selected metrics on the system
  • Specify which metrics are recorded on the system and how often

6.1. Modifying the pmlogger configuration file with pmlogconf

When the pmlogger service is running, PCP logs a default set of metrics on the host.

Use the pmlogconf utility to check the default configuration. If the pmlogger configuration file does not exist, pmlogconf creates it with a default metric values.

Prerequisites

Procedure

  1. Create or modify the pmlogger configuration file: 

    # pmlogconf -r /var/lib/pcp/config/pmlogger/config.default
  2. Follow pmlogconf prompts to enable or disable groups of related performance metrics and to control the logging interval for each enabled group.

Additional resources

6.2. Editing the pmlogger configuration file manually

To create a tailored logging configuration with specific metrics and given intervals, edit the pmlogger configuration file manually. The default pmlogger configuration file is /var/lib/pcp/config/pmlogger/config.default. The configuration file specifies which metrics are logged by the primary logging instance.

In manual configuration, you can:

  • Record metrics which are not listed in the automatic configuration.
  • Choose custom logging frequencies.
  • Add PMDA with the application metrics.

Prerequisites

Procedure

  • Open and edit the /var/lib/pcp/config/pmlogger/config.default file to add specific metrics: 

    # It is safe to make additions from here on ...
#

log mandatory on every 5 seconds {
    xfs.write
    xfs.write_bytes
    xfs.read
    xfs.read_bytes
}

log mandatory on every 10 seconds {
    xfs.allocs
    xfs.block_map
    xfs.transactions
    xfs.log

}

[access]
disallow * : all;
allow localhost : enquire;

Additional resources

6.3. Enabling the pmlogger service

The pmlogger service must be started and enabled to log the metric values on the local machine.

This procedure describes how to enable the pmlogger service.

Prerequisites

Procedure

  • Start and enable the pmlogger service: 

    # systemctl start pmlogger

# systemctl enable pmlogger

Verification steps

  • Verify if the pmlogger service is enabled: 

    # pcp

Performance Co-Pilot configuration on workstation:

platform: Linux workstation 4.18.0-80.el8.x86_64 #1 SMP Wed Mar 13 12:02:46 UTC 2019 x86_64
hardware: 12 cpus, 2 disks, 1 node, 36023MB RAM
timezone: CEST-2
services: pmcd
pmcd: Version 4.3.0-1, 8 agents, 1 client
pmda: root pmcd proc xfs linux mmv kvm jbd2
pmlogger: primary logger: /var/log/pcp/pmlogger/workstation/20190827.15.54

Additional resources

6.4. Setting up a client system for metrics collection

This procedure describes how to set up a client system so that a central server can collect metrics from clients running PCP.

Prerequisites

Procedure

  1. Install the pcp-system-tools package: 

    # dnf install pcp-system-tools

  2. Configure an IP address for pmcd: 

    # echo "-i 192.168.4.62" >>/etc/pcp/pmcd/pmcd.options

    Replace 192.168.4.62 with the IP address, the client should listen on.

    By default, pmcd is listening on the localhost.

  3. Configure the firewall to add the public zone permanently: 

    # firewall-cmd --permanent --zone=public --add-port=44321/tcp
success

# firewall-cmd --reload
success

  4. Set an SELinux boolean: 

    # setsebool -P pcp_bind_all_unreserved_ports on

  5. Enable the pmcd and pmlogger services: 

    # systemctl enable pmcd pmlogger
# systemctl restart pmcd pmlogger

Verification steps

  • Verify if the pmcd is correctly listening on the configured IP address: 

    # ss -tlp | grep 44321
LISTEN   0   5     127.0.0.1:44321   0.0.0.0:*   users:(("pmcd",pid=151595,fd=6))
LISTEN   0   5  192.168.4.62:44321   0.0.0.0:*   users:(("pmcd",pid=151595,fd=0))
LISTEN   0   5         [::1]:44321      [::]:*   users:(("pmcd",pid=151595,fd=7))

Additional resources

6.5. Setting up a central server to collect data

This procedure describes how to create a central server to collect metrics from clients running PCP.

Prerequisites

Procedure

  1. Install the pcp-system-tools package: 

    # dnf install pcp-system-tools

  2. Create the /etc/pcp/pmlogger/control.d/remote file with the following content: 

    # DO NOT REMOVE OR EDIT THE FOLLOWING LINE
$version=1.1

192.168.4.13 n n PCP_ARCHIVE_DIR/rhel7u4a -r -T24h10m -c config.rhel7u4a
192.168.4.14 n n PCP_ARCHIVE_DIR/rhel6u10a -r -T24h10m -c config.rhel6u10a
192.168.4.62 n n PCP_ARCHIVE_DIR/rhel8u1a -r -T24h10m -c config.rhel8u1a
192.168.4.69 n n PCP_ARCHIVE_DIR/rhel9u3a -r -T24h10m -c config.rhel9u3a

    Replace 192.168.4.13, 192.168.4.14, 192.168.4.62 and 192.168.4.69 with the client IP addresses.

  3. Enable the pmcd and pmlogger services: 

    # systemctl enable pmcd pmlogger
# systemctl restart pmcd pmlogger

Verification steps

  • Ensure that you can access the latest archive file from each directory: 

    # for i in /var/log/pcp/pmlogger/rhel*/*.0; do pmdumplog -L $i; done
Log Label (Log Format Version 2)
Performance metrics from host rhel6u10a.local
  commencing Mon Nov 25 21:55:04.851 2019
  ending     Mon Nov 25 22:06:04.874 2019
Archive timezone: JST-9
PID for pmlogger: 24002
Log Label (Log Format Version 2)
Performance metrics from host rhel7u4a
  commencing Tue Nov 26 06:49:24.954 2019
  ending     Tue Nov 26 07:06:24.979 2019
Archive timezone: CET-1
PID for pmlogger: 10941
[..]

    The archive files from the /var/log/pcp/pmlogger/ directory can be used for further analysis and graphing.

Additional resources

6.6. Replaying the PCP log archives with pmrep

After recording the metric data, you can replay the PCP log archives. To export the logs to text files and import them into spreadsheets, use PCP utilities such as pcp2csv, pcp2xml, pmrep or pmlogsummary.

Using the pmrep tool, you can:

  • View the log files
  • Parse the selected PCP log archive and export the values into an ASCII table
  • Extract the entire archive log or only select metric values from the log by specifying individual metrics on the command line

Prerequisites

Procedure

  • Display the data on the metric: 

    $ pmrep --start @3:00am --archive 20211128 --interval 5seconds --samples 10 --output csv disk.dev.write
Time,"disk.dev.write-sda","disk.dev.write-sdb"
2021-11-28 03:00:00,,
2021-11-28 03:00:05,4.000,5.200
2021-11-28 03:00:10,1.600,7.600
2021-11-28 03:00:15,0.800,7.100
2021-11-28 03:00:20,16.600,8.400
2021-11-28 03:00:25,21.400,7.200
2021-11-28 03:00:30,21.200,6.800
2021-11-28 03:00:35,21.000,27.600
2021-11-28 03:00:40,12.400,33.800
2021-11-28 03:00:45,9.800,20.600

    The mentioned example displays the data on the disk.dev.write metric collected in an archive at a 5 second interval in comma-separated-value format.

    Note

    Replace 20211128 in this example with a filename containing the pmlogger archive you want to display data for.

Additional resources

6.7. Enabling PCP version 3 archives

Performance Co-Pilot (PCP) archives store historical values of PCP metrics recorded from a single host and support retrospective performance analysis. PCP archives contain all the important metric data and metadata needed for offline or offsite analysis. These archives can be read by most PCP client tools or dumped raw by the pmdumplog tool.

From PCP 6.0, version 3 archives are supported in addition to version 2 archives. Version 2 archives remain the default and will continue to receive long-term support for backwards compatibility purposes in addition to version 3 archives receiving long-term support from RHEL 9.2 and on.

Using PCP version 3 archives offers the following benefits over version 2:

  • Support for instance domain change-deltas
  • Y2038-safe timestamps
  • Nanosecond-precision timestamps
  • Arbitrary timezones support
  • 64-bit file offsets used for individual volumes larger than 2GB

Prerequisites

Procedure

  1. Open the /etc/pcp.conf file in a text editor of your choice and set the PCP archive version: 

    PCP_ARCHIVE_VERSION=3

  2. Restart the pmlogger service to apply your configuration changes: 

    # systemctl restart pmlogger.service
  3. Create a new PCP archive log using your new configuration. For more information, see Logging performance data with pmlogger.

Verification

  • Verify the version of the archive created with your new configuration: 

    # pmloglabel -l /var/log/pcp/pmlogger/20230208
Log Label (Log Format Version 3)
Performance metrics from host host1
        commencing Wed Feb   08 00:11:09.396 2023
        ending           Thu  Feb   07 00:13:54.347 2023

Additional resources