Can large page improve timesten performance on aix??

Question

hello, chris:
Can large page imporove timesten performance on aix? we havenot test it yet, I just want to know whether it is ok?? thank you.

Answer 1

Enabling large page support on AIX may help performance under some circumstances (typically with large datastores). TimesTen does support use of large pages on AIX and no special action is needed on the TimesTen side to utilise large pages. Here is some information on this which should eventually appear in the TimesTen documentation.
The TimesTen shared memory segment for AIX has been created with the flags
( SHM_PIN | SHM_LGPAGE) necessary for large page support for many releases.
It used to be the case that special kernel flags needed to be enabled so it
was never documented as being supported. Subsequent AIX releases have made
enabling large pages a matter of system administration.
1) Enable capabilities (chuser)
2) Configure page pool (vmo -r)
3) Enable memory pining (vmo -p)
4) [restart timesten daemons]
The documentation is quoted below.
AIX maintains separate 4 KB and 16 MB physical memory pools. You can
specify the amount of physical memory in the 16 MB memory pool using the vmo
command. Starting with AIX 5.3, the large page pool is dynamic, so the amount
of physical memory that you specify takes effect immediately and does not
require a system reboot. The remaining physical memory backs the 4 KB virtual
pages.
AIX treats large pages as pinned memory. AIX does not provide paging
support for large pages. The data of an application that is backed by large
pages remains in physical memory until the application completes. A security
access control mechanism prevents unauthorized applications from using large
pages or large page physical memory. The security access control mechanism
also prevents unauthorized users from using large pages for their
applications. For non-root user ids, you must enable the CAP_BYPASS_RAC_VMM
capability with the chuser command in order to use large pages. The following
example demonstrates how to grant the CAP_BYPASS_RAC_VMM capability as the
superuser:
# chuser capabilities=CAP_BYPASS_RAC_VMM,CAP_PROPAGATE <user id>
The system default is to not have any memory allocated to the large page
physical memory pool. You can use the vmo command to configure the size of
the large page physical memory pool. The following example allocates 4 GB to
the large page physical memory pool:
# vmo -r -o lgpg_regions=64 -o lgpg_size=16777216
To use large pages for shared memory, you must enable the SHM_PIN shmget()
system call with the following command, which persists across system reboots:
# vmo -p -o v_pinshm=1
To see how many large pages are in use on your system, use the vmstat -l
command as in the following example:
# vmstat -l
kthr memory page faults cpu large-page
r b avm fre re pi po fr sr cy in sy cs us sy id wa alp flp
2 1 52238 124523 0 0 0 0 0 0 142 41 73 0 3 97 0 16 16
From the above example, you can see that there are 16 active large pages, alp, and
16 free large pages, flp.
Documentation is at:
http://publib.boulder.ibm.com/infocenter/pseries/v5r3/index.jsp?topic=/com.ibmaix.prftungd/doc/prftungd/large_page_ovw.htm
Chris