The SHMTOTAL configuration parameter and memory utilization

The SHMTOTAL configuration parameter places an absolute upper limit on the amount of shared memory that an instance of the database server can use.

If the SHMTOTAL configuration parameter is set to 0 or left unassigned, the database server continues to attach additional shared memory as needed until no virtual memory is available on the system.

You can usually set the SHMTOTAL configuration parameter to 0, except in the following cases:
  • You must limit the amount of virtual memory that the database server uses for other applications or other reasons.
  • Your operating system runs out of swap space and performs abnormally. In this case, you can set SHMTOTAL to a value that is a few megabytes less than the total swap space that is available on your computer.
  • You are using automatic low memory management.

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