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Applies to SUSE Linux Enterprise Server for SAP Applications 12 SP4

8 Tuning

This chapter presents information about tuning SLES-SAP to work optimally with SAP applications.

Note
Note: Choosing between sapconf and saptune

On SUSE Linux Enterprise Server for SAP Applications you have the choice between sapconf and saptune. However, saptune is the more elaborate tool that offers more features.

8.1 Kernel: Page-Cache Limit

Problem

The kernel swaps out rarely accessed memory pages to use freed memory pages as cache to speed up file system operations, for example during backup operations.

SAP NetWeaver and SAP HANA use large amounts of memory for accelerated access to business data. Parts of this memory are rarely accessed. When a user request needs to access paged-out memory, the response time is poor. It is even worse when an SAP application running on Java incurs a Java garbage collection: The system starts heavy page-in (disk I/O) activity and has a poor response time for an extended period of time.

Solution

SUSE Linux Enterprise Server for SAP Applications includes a kernel tuning option that allows the system administrator to limit the amount of page cache that the kernel uses when there is competition between application memory and page cache. This option tells the kernel that when the page cache is filled to the configured limit, application memory is more important and should thus not be paged out. No pages will be paged out if the memory footprint of the workload plus the configured page-cache limit do not exceed the amount of physical RAM in the system.

These kernel options are available for configuration:

  • vm.pagecache_limit_mb (/proc/sys/vm/pagecache_limit_mb)

  • vm.pagecache_limit_ignore_dirty (/proc/sys/vm/pagecache_limit_ignore_dirty)

Tip
Tip: Use sapconf to Configure Parameters

The parameters vm.pagecache_limit_mb and vm.pagecache_limit_ignore_dirty are also configured by the tuned profiles delivered with sapconf.

For more information, see Section 8.2, “Tuning Systems with sapconf.

Important
Important: The Following Are Example Values

The values reproduced in Example 8.1, “Permanently Setting the Page-Cache Limit” are example values only. Do not set the following parameters on a productive system without first trying and calibrating them on a non-productive system.

If your system does not exhibit page-cache limit issues under the workloads it is running, there is no need to adjust these parameters.

For more information, see SAP Note 1557506: Linux Paging Improvements (https://launchpad.support.sap.com/#/notes/1557506).

Example 8.1: Permanently Setting the Page-Cache Limit

For permanent use, add both parameters to /etc/sysctl.conf, for example:

vm.pagecache_limit_mb = 1024
vm.pagecache_limit_ignore_dirty = 2

8.2 Tuning Systems with sapconf

The package sapconf contains the tuned profile sap-netweaver. This single tuning profile sets recommended parameters for SAP applications, in particular SAP NetWeaver, SAP HANA, and SAP HANA-based applications.

sapconf consists of two primary parts:

  • A systemd service that ensures tuned and related services are running and the sap-netweaver profile is applied.

  • The tuned profile sap-netweaver that applies configured sapconf tuning parameters using a script and configuration files.

    (The profile sap-hana is currently identical to sap-netweaver. sapconf additionally includes the profiles sap-ase and sap-bobj which are currently not recommended for use.)

To use sapconf, install the package sapconf on your system.

Note
Note: sapconf Utility

The command-line utility sapconf is still available in SUSE Linux Enterprise Server for SAP Applications 12 SP4. However, it is no longer the preferred utility to control sapconf.

Starting with SUSE Linux Enterprise Server for SAP Applications 15, the utility sapconf is not included in the package sapconf anymore.

Note
Note: Unified Profiles in SUSE Linux Enterprise Server for SAP Applications 15

In SUSE Linux Enterprise Server for SAP Applications 15 and up, only a single tuned profile, sapconf, is shipped. It is equivalent to the profiles sap-hana/sap-netweaver (both profiles are identical) that are shipped with sapconf in SUSE Linux Enterprise Server for SAP Applications 12 SP4.

8.2.1 Enabling and Disabling sapconf and Viewing Its Status

After the installation of sapconf, tuned is enabled and the sap-netweaver profile is activated. However, if another tuned profile is already enabled, sapconf will not enable its own tuned profile. If you previously made other changes to system tuning, these may be overridden by the profile of sapconf.

To make sure sapconf applies all tuning parameters, reboot the machine after installation.

You can inspect or change the status of sapconf as described in the following:

  • To see the status of the service sapconf:

    root # systemctl status sapconf

    The service should be displayed as active (exited), as it is only responsible for starting tuned and will exit afterward.

  • To start the service sapconf and with it the service tuned:

    root # systemctl start sapconf
  • Should sapconf be disabled, enable and start it with:

    root # systemctl enable --now sapconf
  • To stop the service sapconf and with it the service tuned:

    root # systemctl stop sapconf

    As tuned is also terminated at that point, the vast majority of optimizations which do not require a system reboot to disable are disabled immediately.

  • To disable sapconf, use:

    root # systemctl disable sapconf

    If you have not specifically enabled any of the services that sapconf depends on yourself, this will also disable most tuning parameters and all services used by sapconf.

Similarly, you can inspect and change the status of the underlying service tuned:

  • To see the status of the service tuned:

    root # systemctl status tuned
  • To see which tuned profile is currently in use:

    root # tuned-adm active

    If this command does not return the name of the currently active profile as sap-netweaver, enable that profile:

    root # tuned-adm profile sap-netweaver
Tip
Tip: Additional Services that sapconf Relies On

In addition to the sapconf service itself and the tuned service, sapconf also relies on the following two services:

  • sysstat collects data on system activity.

  • uuidd which generates time-based UUIDs that are guaranteed to be unique even in settings where many processor cores are involved. This is necessary for SAP applications.

8.2.2 Configuring sapconf

In general, the default configuration of sapconf already uses the parameter values recommended by SAP. However, if you have special needs, you can configure the tool to better suit those.

The configuration of sapconf is split in two parts that can be configured in different ways:

/usr/lib/tuned/sap-netweaver/tuned.conf

This file contains basic parameters. It also calls the script.sh from the same directory.

To configure parameters from this file, copy it to the custom profile directory of tuned under /etc/tuned first and then change values in it. If you change the file in place instead, you will lose the changes you make on the next update of the sapconf package.

Configure the file as described in the following:

Procedure 8.1:
  1. Create a new custom tuned profile directory and copy the file tuned.conf:

    root # mkdir /etc/tuned/sap-netweaver
    root # cp /usr/lib/tuned/sap-netweaver/tuned.conf /etc/tuned/sap-netweaver/
  2. Within the newly copied tuned.conf, fix the reference to script.sh to use an absolute path that points to the script from the original profile:

    script = /usr/lib/tuned/sap-netweaver/script.sh

    Do not instead copy script.sh, as that provokes update compatibility issues for sapconf.

  3. Edit the parameters in /etc/tuned/sap-netweaver/tuned.conf.

After each update to sapconf, make sure to compare the contents of the original and the custom tuned.conf.

Log messages related to this file are written to /var/log/tuned/tuned.log.

/etc/sysconfig/sapconf

This file contains most parameters of sapconf. The parameters from this file are applied using the aforementioned script /usr/lib/tuned/sap-netweaver/script.sh.

This file can be edited directly. All parameters in this file are explained by means of comments and references to SAP Notes which can be viewed at https://launchpad.support.sap.com/.

When sapconf is updated, all customized parameters from this file will be preserved as much as possible. However, sometimes parameters cannot be transferred cleanly to the new configuration file. Therefore, after updating it is advisable to check the difference between the previous custom configuration which during the update is moved to /etc/sysconfig/sapconf.rpmsave and the new version at /etc/sysconfig/sapconf.

Log messages related to this file are written to /var/log/sapconf.log.

When editing either of these files, you will find that some values are commented by means of a # character at the beginning of the line. This means that while the parameter is relevant for tuning, there is no suitable default for it.

Conversely, you can add # characters to the beginning of the line to comment specific parameters. However, you should avoid this practice, as it can lead to sapconf not properly applying the profile.

To apply edited configuration, restart sapconf:

root # systemctl restart sapconf

Confirming that a certain parameter value was applied correctly works differently for different parameters. Hence, the following serves as an example only:

Example 8.2: Checking Parameters

To confirm that the setting for TCP_SLOW_START was applied, do the following:

  • View the log file of sapconf to see whether it applied the value. Within /var/log/sapconf.log, check for a line containing this text:

    Change net.ipv4.tcp_slow_start_after_idle from 1 to 0

    Alternatively, the parameter may have already been set correctly before sapconf was started. In this case, sapconf will not change its value:

    Leaving net.ipv4.tcp_slow_start_after_idle unchanged at 1
  • The underlying option behind TCP_SLOW_START can be manually configured at /proc/sys/net.ipv4.tcp_slow_start_after_idle. To check its actual current value, use:

    root # sysctl net.ipv4.tcp_slow_start_after_idle

8.2.3 Removing sapconf

To remove sapconf from a system, uninstall its package with:

root # zypper rm sapconf

Note that when doing this, dependencies of sapconf will remain installed. However, the services sysstat and tuned will go into a disabled state. If either is still relevant to you, make sure to enable it again.

Certain parameters and files are not removed when sapconf is uninstalled. For more information, see the man page man 7 sapconf, section PACKAGE REQUIREMENTS.

8.2.4 For More Information

The following man pages provide additional information about sapconf:

  • High-level overview of tuning parameters used by sapconf: man 7 tuned-profiles-sapconf

  • Detailed description of all tuning parameters set by sapconf: man 5 sapconf

  • Information about configuring and customizing the sapconf profile: man 7 sapconf

Also see the blog series detailing the updated version of sapconf at https://www.suse.com/c/a-new-sapconf-is-available/.

8.3 Tuning Systems with saptune

Using saptune, you can tune a system for SAP NetWeaver, SAP HANA/SAP BusinessObjects, and SAP S/4HANA applications. This method relies on the system tuning service tuned.

If you used the SAP Installation Wizard to install an SAP application, tuned is usually already active and configured with a profile for the application you installed.

If you did not use the SAP Installation Wizard to install an SAP application, make sure that the packages tuned and saptune are installed on your system.

8.3.1 Enabling saptune to Tune for an SAP Application

  1. To tune a system, first find a tuning solutions. To find the appropriate solution, use:

    tux > saptune solution list

    saptune knows the following tuning solutions (groups of SAP notes):

    • BOBJ Solution for running SAP BusinessObjects.

    • HANA Solution for running a SAP HANA database.

    • MAXDB Solution for running a SAP MaxDB database.

    • NETWEAVER Solution for running SAP NetWeaver application servers.

    • S4HANA-APPSERVER Solution for running SAP S/4HANA application servers (identical to SAP NetWeaver solution).

    • S4HANA-APP+DBSolution for running both SAP S/4HANA application servers and SAP HANA on the same host (identical to SAP NetWeaver + SAP HANA solution).

    • S4HANA-DBSERVER Solution for running the SAP HANA database of an SAP S/4HANA installation (identical to SAP HANA solution)

    • SAP-ASE Solution for running an SAP Adaptive Server Enterprise database.

    Alternatively, you can tune the computer according to recommendations from specific SAP Notes. A list of notes that you can tune for is available via:

    root # saptune note list
    • To set up saptune with a preconfigured solution, use:

      root # saptune solution apply SOLUTION
    • To set up saptune for the recommendations of a specific SAP Note, use:

      root # saptune note apply NOTE
    Note
    Note: Combining Optimizations

    You can combine solutions and notes. However, only one solution can be active at a time. In rare cases, notes can have conflicting options or parameters. To avoid conflicts, order your notes, keeping in mind that the last note always overrides conflicting options or parameters of previous notes.

  2. To start saptune and enable it at boot, make sure to run the following command:

    root # saptune daemon start

In the background, saptune applies a tuned profile also named saptune that is dynamically customized according to selected solutions and notes. Using tuned-adm list, you can also see this profile.

8.3.2 Customizing a SAP Note

Every SAP note can be configured freely with:

root # saptune note customise

The command includes changing a value or disabling a parameter.

8.3.3 Creating a new SAP Note

It is possible to create a new SAP note with:

root # saptune note create

All features of saptune are available.

8.3.4 Deleting a SAP Note

This command allows to delete a created note including the corresponding override after confirmation:

root # saptune note delete

The note may not be applied at the time. SAP notes shipped by saptune cannot be deleted. Instead, the override file is removed when available.

8.3.5 Renaming a SAP Note

This command allows to rename a created note including the corresponding override after confirmation:

root # saptune note rename

The note may not be applied at the time. SAP notes shipped by saptune cannot be renamed.

8.3.6 Showing the Configuration of a SAP Note

The shipped configuration of a note can be listed with:

root # saptune note show

8.3.7 Verifying a SAP Note or a SAP Solution

The commands saptune note verify NOTE and saptune solution verify SOLUTION list the following data for each active or requested note:

  • The parameter name

  • The expected value (default)

  • A configured override (created using saptune customise)

  • The current system value

  • Whether the current state is in accordance with the SAP recommendation

8.3.8 Simulating the Application of a SAP Note or a SAP Solution

To show each parameter of a note, use:

root # saptune note simulate

To show each parameter of a solution, use:

root # saptune solution simulate

It lists the current system value and the expected values (default and override).

8.3.9 Disabling saptune

To disable saptune and to stop and disable tuned run:

root # saptune daemon stop

8.3.10 Tuning Kernel Parameters Manually Using sysctl

In addition to or instead of tuning kernel parameters using saptune, you can also use sysctl to make manual adjustments to kernel parameters. However, such changes using sysctl do not persist across reboots by default. To make them persist across reboots, add them to the file /etc/sysctl.conf (or another configuration file read by sysctl).

Tip
Tip

If you plan to configure sysctl parameters for your SAP system, consider to use saptune as a central instance for managing your system configuration.

For more information about sysctl, see the man pages sysctl(8), sysctl.conf(5), and sysctl.d(5).

8.3.11 For More Information

See the following man pages:

  • man 8 saptune

  • man 8 saptune_v1

  • man 8 saptune_v2

  • man 8 saptune-migrate

  • man 8 saptune-note

Also see the project home page https://github.com/SUSE/saptune/.

8.4 Tuning Kernel Parameters Manually Using sysctl

In addition to or instead of tuning kernel parameters using sapconf/saptune, you can also use sysctl to make manual adjustments to kernel parameters. However, such changes using sysctl do not persist across reboots by default. To make them persist across reboots, add them to one of the configuration files read by sysctl).

For more information about sysctl, see the man pages sysctl(8), sysctl.conf(5), and sysctl.d(5).

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