DB2 Version 9.7 for Linux, UNIX, and Windows

Enabling large page support (AIX)

To enable large page support in DB2® database systems on AIX® operating systems, you must configure some operating system parameters and then set the DB2_LARGE_PAGE_MEM registry variable.

About this task

In addition to the traditional page size of 4 KB, the POWER4 processors (and higher) on System z® also support a 16 MB page size. Applications such as IBM® DB2 Version 9.7 for AIX, that require intensive memory access and that use large amounts of virtual memory can gain performance improvements by using large pages.

Note:

Setting the DB2_LARGE_PAGE_MEM registry variable also implies that the memory is pinned.
You should be extremely cautious when configuring your system for pinning memory and supporting large pages. Pinning too much memory results in heavy paging activities for the memory pages that are not pinned. Allocating too much physical memory to large pages will degrade system performance if there is insufficient memory to support the 4 KB pages.

Restrictions

Enabling large pages prevents the self-tuning memory manager from automatically tuning overall database memory consumption, so it should only be considered for well-defined workloads that have relatively static database memory requirements.

Before you begin

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

Procedure

To enable large page support in DB2 database systems on AIX operating systems:

Configure your AIX server for large page support by issuing the vmo command with the following flags:
```
vmo -r -o lgpg_size=LargePageSize -o lgpg_regions=LargePages
```
where LargePageSize specifies the size in bytes of the hardware-supported large pages, and LargePages specifies the number of large pages to reserve. For example, if you need to allocate 25 GB for large page support, run the command as follows:
```
vmo -r -o lgpg_size=16777216 -o lgpg_regions=1600
```
For detailed instructions on how to run the vmo command, refer to your AIX manuals.
Run the bosboot command so that the vmo command that you previously run will take effect following the next system boot.
After the server comes up, enable it for pinned memory. Issue the vmo command with the following flags:
```
vmo -o v_pinshm=1
```
Use the db2set command to set the DB2_LARGE_PAGE_MEM registry variable to DB, then start the DB2 database manager. For example:
```
db2set DB2_LARGE_PAGE_MEM=DB
db2start
```

Results

When these steps are complete, the DB2 database system directs the operating system to use large page memory for the database shared memory region.