16.10 - About Shared Memory - Teradata Database

Teradata Database Administration

Product
Teradata Database
Release Number
16.10
Release Date
April 2018
Content Type
Administration
Publication ID
B035-1093-161K
Language
English (United States)

The system determines how memory is shared between the OS and FSGCache. For example, the following figure illustrates how the system calculates FSG Cache for a Teradata Database system with 16 GB shared memory.



When Linux boots, PDE:

  • Determines how much memory the OS is already using.

    In the example, memory is shown to be 500 MB. This number may vary depending on the system configuration.

  • Leaves to the OS an amount of memory equal to the number of vprocs times the memory allocated to each vproc.

    In the example, this amount is 90 MB for each of the 28 vprocs.

    Vprocs include AMPs, PEs, the Gateway, and the Node vproc.
  • Calculates the FSG Cache by (1) subtracting the OS-managed memory from total memory size and then (2) applying a FSG Cache% to that amount.
    To calculate the FSG Cache per AMP, divide the FSG Cache by the number of AMPs.

    The amount of OS-managed memory is 3020 MB and the FSG Cache, if the FSG Cache% is 100%, would be 13364 MB.

    If the FSG Cache% were set to 65%, then the FSG Cache would be 8687 MB, and the additional free memory would be 13364 MB minus 8687 MB, or 4677 MB.

    If you want to run applications with memory requirements unknown to Teradata Database software, reduce the FSG Cache% to leave memory for the applications.

    FSG Cache is managed in multiples of 4 KB up to 128 KB, and then in increments of 256 KB, 512 KB, and 1 MB.

Reserving Additional Free Memory for Applications

To reserve 20% of the FSG Cache for applications over and above the 90 MB/vproc reserved for the OS, go to the DBS screen and set FSG Cache percent to 80. The system assigns 80% of the FSG Cache to FSG and leaves the remaining 20% for other applications.

For information on ctl, see Utilities.