nflocks(5)                                                       nflocks(5)
                          Tunable Kernel Parameters



 NAME    [Toc]    [Back]
      nflocks - maximum number of file locks

 VALUES    [Toc]    [Back]
    Failsafe
      1024

    Default    [Toc]    [Back]
      The default value is computed at runtime and depends on the amount of
      physical memory on the system.  For small memory systems (less than
      1GB), the default is 1200.  For systems with more than 1GB of memory,
      the default is 4096, or 4K.

    Allowed values    [Toc]    [Back]
      The minimum value is 50.  The maximum value is 0x1000000.

      Specify a positive integer value.

 DESCRIPTION    [Toc]    [Back]
      The nflocks tunable represents the maximum number of file locks that
      are available system-wide.

    Who Is Expected to Change This Tunable?
      This tunable should be changed on systems expected to run applications
      with large number of file locks.  When changing this number note that
      one file may have several locks, and databases that use lockf() or
      fcntl() may need an exceptionally large number of locks.

    Restrictions on Changing    [Toc]    [Back]
      This tunable is dynamic (tuning will take effect immediately on the
      running system).  When the value of nflocks is dynamically tuned it
      cannot be set to a value lower than the current number of file locks
      in the running kernel.

    When Should the Value of This Tunable Be Raised?
      The value should be increased when large numbers of file locks are
      expected to be used simultaneously.

    What are the Side Effects of Raising the Value?
      The kernel allocates a portion of memory proportional to the new value
      of nflocks and frees memory proportional to the old value.  Additional
      memory is consumed as new locks are created.

    When Should the Value of This Tunable Be Lowered?
      The value can be lowered to limit the number of available file locks
      on a system and reduce memory consumption.

    What are the Side Effects of Lowering the Value?
      The kernel allocates a portion of memory proportional to the new value
      of nflocks, and frees memory proportional to the old value.
      Additional memory may be released to the system to be used for other



 Hewlett-Packard Company            - 1 -      HP-UX 11i Version 2: Sep 2004






 nflocks(5)                                                       nflocks(5)
                          Tunable Kernel Parameters



      purposes if the usage was ever higher than this new value.

    What Other Tunable Values Should Be Changed at the Same Time?
      None.

 WARNINGS    [Toc]    [Back]
      Setting nflocks to the maximum value (0x1000000) will result in a
      large memory allocation (~.5GB).  A request to change the value of
      nflocks will fail with [ENOMEM] set if there is either not enough free
      memory or the remaining free memory would be so small as to
      potentially hinder system performance.

      All HP-UX kernel tunable parameters are release specific.  This
      parameter may be removed or have its meaning changed in future
      releases of HP-UX.

      Installation of optional kernel software, from HP or other vendors,
      may cause changes to tunable parameter values.  After installation,
      some tunable parameters may no longer be at the default or recommended
      values.  For information about the effects of installation on tunable
      values, consult the documentation for the kernel software being
      installed. For information about optional kernel software that was
      factory installed on your system, see HP-UX Release Notes at
      http://docs.hp.com.

 AUTHOR    [Toc]    [Back]
      nflocks was developed by HP.

 SEE ALSO    [Toc]    [Back]
      kctune(1M), sam(1M), gettune(2), settune(2), fcntl(2), lockf(2).


 Hewlett-Packard Company            - 2 -      HP-UX 11i Version 2: Sep 2004