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Chapter 6. Tuning resource limits

Directory Server provides several settings to tune the amount of resources an instance uses. You can change them using the command line or the web console.

6.1. Updating resource limit settings using the command line

This section provides a general procedure how to change resource limit settings. Adjust the settings according to your environment.


  1. Update the performance settings:

    # dsconf -D "cn=Directory Manager" ldap:// config replace parameter_name=value

    You can set the following parameters:

    • nsslapd-threadnumber: Sets the number of worker threads.
    • nsslapd-maxdescriptors: Sets the maximum number of file descriptors.
    • nsslapd-timelimit: Sets the search time limit.
    • nsslapd-sizelimit: Sets the search size limit.
    • nsslapd-pagedsizelimit: Sets the paged search size limit.
    • nsslapd-idletimeout: Sets the idle connection timeout.
    • nsslapd-ioblocktimeout: Sets the input/output (I/O) block timeout.
    • nsslapd-ndn-cache-enabled: Enables or disables the normalized DN cache.
    • nsslapd-ndn-cache-max-size: Sets the normalized DN cache size, if nsslapd-ndn-cache-enabled is enabled.
    • nsslapd-outbound-ldap-io-timeout: Sets the outbound I/O timeout.
    • nsslapd-maxbersize: Sets the maximum Basic Encoding Rules (BER) size.
    • nsslapd-maxsasliosize: Sets the maximum Simple Authentication and Security Layer (SASL) I/O size.
    • nsslapd-listen-backlog-size: Sets the maximum number of sockets available to receive incoming connections.
    • nsslapd-max-filter-nest-level: Sets the maximum nested filter level.
    • nsslapd-ignore-virtual-attrs: Enables or disables virtual attribute lookups.
    • nsslapd-connection-nocanon: Enables or disables reverse DNS lookups.
    • nsslapd-enable-turbo-mode: Enables or disables the turbo mode feature.

      For further details, see the descriptions of the parameters in the Configuration and schema reference

  2. Restart the instance:

    # dsctl instance_name restart

6.2. Updating resource limit settings using the web console

This section provides a general procedure how to change resource limit settings. Adjust the settings according to your environment.


  • You are logged in to the instance in the web console.


  1. Navigate to ServerTuning & Limits.
  2. Update the settings. Optionally, click Show Advanced Settings to display all settings.

    tuning and limits
  3. Click Save Settings.
  4. Click ActionsRestart Instance.

6.3. Disabling the Transparent Huge Pages feature

Transparent Huge Pages (THP) is the memory management feature in Linux, which reduces the overhead of Translation Lookaside Buffer (TLB) checks on machines with large amounts of memory by using larger memory pages. The THP feature is enabled by default on RHEL systems and supports 2 MB memory pages.

The THP feature, however, works best when enabled on large, contiguous allocation patterns and can degrade performance on small, sparse allocation patterns that are typical to the Red Hat Directory Server. The resident memory size of the process might eventually exceed the limit and impact performance or get terminated by the out of memory (OOM) killer.


It is recommended to disable THP on RHEL systems with Red Hat Directory Server installed to avoid performance and memory consumption problems.


  1. Check the current status of transparent huge pages by running the following command:

    # cat /sys/kernel/mm/transparent_hugepage/enabled
  2. If the transparent huge pages feature is active, disable it either at boot time or run time:

    • Disable the transparent huge pages at boot time by appending the following to the kernel command line in the grub.conf file:

    • Disable transparent huge pages at run time by running the following commands:

      # echo never > /sys/kernel/mm/transparent_hugepage/enabled
      # echo never > /sys/kernel/mm/transparent_hugepage/defrag