Pinning Db2 database shared memory (AIX)

To pin Db2 database shared memory on AIX® operating systems, you must configure some operating system parameters and then set the DB2_PINNED_BP registry variable.

Before you begin

You must have root authority to perform the AIX operating system commands.

About this task

The advantage of having portions of memory pinned is that when you access a page that is pinned, you can retrieve the page without going through the page replacement algorithm. A disadvantage is that you must take care to ensure that the system is not overcommitted, as the operating system will have reduced flexibility in managing memory. Pinning too much memory results in heavy paging activities for the memory pages that are not pinned.


Restrictions

If you set the DB2_PINNED_BP registry variable to YES, self tuning for database shared memory cannot be enabled.

Procedure

To pin Db2 database shared memory on AIX operating systems:

  1. Configure the AIX operating system to enable pinned memory.
    Issue the vmo command with the following flags:
    vmo -p -o v_pinshm=1

    For detailed instructions on how to run the vmo command, refer to your AIX manuals.

  2. (Optional) If you are using medium sized pages (which is the default behavior), ensure that the Db2 instance owner has the CAP_BYPASS_RAC_VMM and CAP_PROPAGATE capabilities.
    For example:
    chuser capabilities=CAP_BYPASS_RAC_VMM,CAP_PROPAGATE db2inst1
    where db2inst1 is the Db2 instance owner user ID.
  3. Run the bosboot command so that the vmo command will take effect following the next system boot.
  4. After the server comes up, enable the Db2 database system for pinned memory.
    1. Issue the db2set command to set the DB2_PINNED_BP registry variable to YES.
    2. Start the Db2 database manager.
    For example:
    db2set DB2_PINNED_BP=YES
db2start

Results

When these steps are complete, the Db2 database system directs the operating system to pin the Db2 database shared memory.