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

Obsolete AdvFS system parameters

The following AdvFS tunable parameters are obsolete since the integration of AdvFS with the regular

UBC mechanisms in Tru64 UNIX V5.1:

• AdvfsCacheMaxPercent

• AdvfsCacheHashSize

• AdvfsCleanupPercent

• AdvfsMaxFreeAccessPercent

• AdvfsMinFreeAccess

Those parameters are no longer used to tune the AdvFS buffer cache and should be removed from

/etc/sysconfigtab.

Use the UBC parameters ubc_maxpercent and ubc_minpercent to tune the file system cache.

VFS Subsystem

Modify the following tunable parameters in the vfs subsystem section of /etc/sysconfigtab.

fifo_do_adaptive

This is one of the tunable parameters where the default value may not have been chosen perfectly if

the system is running as a database server.

The default setting of the fifo_do_adaptive parameter enables an alternate algorithm in the FIFO

routines (used for pipes). The original intent was to come up with an optimal working set size and

then attempt to perform fewer data transfer operations (but of a larger size).

This works reasonably well for applications that perform data transfers of a uniform or near-uniform

size. This does not work so well for some applications that perform data transfers of a random size

(for example, those applications that started out performing transfers so that the FIFO code

determined an optimal transfer size), and works poorly for some applications in which the peer

processes operate in sync (meaning process A transfers data to process B and then waits for process

B's response).

By disabling the fifo_do_adaptive parameter, the performance for some applications will

degrade and improve for others. The performance change depends on how the pipes get used.

For Oracle environments, HP recommends the fifo_do_adaptive = 0 setting.

smoothsync

The smoothsync_age attribute is currently configured at the default setting of 30 seconds. The

smoothsync_age attribute is used to determine how a buffered dirty page is allowed to age before

it is written to disk. With Oracle, buffered I/O is utilized when accessing redo logs and archive logs.

Write requests to the redo and archive logs flow into UBC where they are eventually transferred,

usually asynchronously, to physical storage by some synchronization mechanism (smoothsync,

fsync, and so on). smoothsync provides the behavior that each written page will age for

smoothsync_age seconds in UBC before being flushed to disk.

Reducing the smoothsync_age time allows dirty buffer writes to occur sooner after they arrive,

which has the effect of keeping the I/O pipe more evenly loaded at all times. The downside is that

frequently updated buffers may be written multiple times; however, this is unlikely to happen on an

Oracle database server. A reasonable starting point for smoothsync_age on most modern systems

is 4 (seconds). Faster CPUs and networks and slower storage systems all call for smaller values of

smoothsync_age.

To change the time of smoothsync_age attribute, make the following change in /etc/inittab: