Tuning HP Tru64 UNIX V5.1A and V5.1B for Oracle

5
Key Tunable Parameters
This section describes the various kernel parameter changes that HP recommends for use in an Oracle
environment.
HP recommends that only those parameters that are changed from the default value be included in the
/etc/sysconfigtab file. HP further recommends that changes to the /etc/sysconfigtab file
are made using the sysconfigdb command.
When the version of the release to which a parameter applies is not explicitly mentioned, then the
recommendation is valid for both Tru64 UNIX V5.1A and Tru64 UNIX V5.1B systems.
VM Subsystem
The following sections describe the tunable parameters to modify in the VM subsystem section of
/etc/sysconfigtab.
new_wire_method
Since the introduction of the light-weight wiring (vm:new_wire_method=1) algorithm as a means to
wire pages in memory, there have been several issues that have prevented its successful use. Some
examples of such problems were:
• An interaction between asynchronous I/O (AIO) and light-weight wiring resulting in high system
times
• The combination of granularity hints memory (gh_regions > 0 or rad_gh_regions > 0) with
light-weight wiring, preventing the successful start-up of Oracle
Since there was no negative impact to the use of the regular wiring algorithm, the recommendation
has, for many years, been to disable light-weight wiring; that is, new_wire_method = 0.
With the introduction of Tru64 UNIX V5.1B, all known problems with light-weight wiring have been
fixed and light-weight wiring has become the preferred page-wiring algorithm for HP. In addition,
Oracle has also qualified Oracle 9i (9.2) and later releases with light weight wiring.
In the Tru64 UNIX V5.1B PK3 Service PAK, additional fixes were introduced to the AIO mechanism
that may cause asynchronous I/Os to be slow in combination with regular style page wiring.
Therefore, Oracle now requires that systems running Tru64 UNIX V5.1B PK3 Service PAK or later use
light-weight page wiring; that is, new_wire_method = 1.
In summary, HP recommends the following values for new_wire_method:
• new_wire_method = 1 when running Oracle on Tru64 UNIX V5.1B PK3 Service PAK or later
• new_wire_method = 0 when running Oracle on Tru64 UNIX V5.1B PK2 or earlier (including
previous releases of Tru64 UNIX)
Note: In Tru64 UNIX V5.1B-3 (PK5) and later, the vm:new_wire_method kernel parameter is
deprecated. Tuning of this parameter is no longer possible and light-weight wiring is always enabled.
ubc_maxpercent
As of Oracle 8.1.7, AdvFS direct I/O was enabled by default, resulting in there no longer being a
need to artificially restrict the UBC. Before the availability of direct I/O, HP recommended that the
amount of memory used by the UBC should be reduced to prevent double-caching of Oracle data by
the file system. Now that the AdvFS file system is fully integrated with the regular UBC mechanisms,
double-caching is no longer an issue for Tru64 UNIX and Oracle based database environments when
using the direct I/O settings recommended by Oracle. However, setting this tunable parameter to a
low value may cause contention in the kernel and have a negative impact on performance.