dataprefetch

[Carlos Muñoz_1]

hello, good day. I reader a note of oracle that it indicates to change parameter dataprefetch to disable( this parameter it is modified in the starting of the machine and is of firmware) in the fisical partitions of superdome. This improvement the yield with oracle.Do you now something of this?

thank you.

[Kent Ostby]

This is done because by turning off dataprefetch, you use the 64-byte cache lines and these are more efficient because of Oracle's use of 64-byte aligned semaphores.

So there is less conversion from the HW to the SW level.

Best regards,

Kent M. Ostby

[David de Beer]

Carlos,

Look at the following link regarding Oracle and HP tuning - with specific reference to your question on disabling Data Prefetch on HP SuperDome systems:

http://www.cs.nott.ac.uk/TSG/manuals/databases/oracle/standard/a90347/appb_hp.htm

It covers the following issues:
HP SCHED_NOAGE Scheduling Policy
Lightweight Timer Implementation
Asynchronous I/O
Disabling Data Prefetch on the HP SuperDome for Oracle

Here is the part that you will find relevant:

Disabling Data Prefetch on the HP SuperDome for Oracle

HP SuperDome systems have a data prefetch feature that might impair Oracle performance in update or insert intensive applications. Oracle Corporation and Hewlett-Packard Corporation recommend that you disable this feature for these types of applications.

Prefetching data usually improves application performance. However, the Oracle server is developed to run well on all HP systems, including those that do not include the prefetch feature. In update and insert intensive applications, enabling the data prefetch feature unintentionally creates contention on redo allocation and redo copy latches. This contention is increased as the number of processors is increased. Disabling the data prefetch feature helps to reduce redo latch contention.

HP SuperDome systems can run multiple instances of the HP-UX 11i operating system on a single server by defining multiple partitions within a SuperDome server. Each partition on a HP SuperDome system acts as a logical server running a single instance of HP-UX. Each system can boot, reboot, and operate independently of other partitions and hardware within the SuperDome system. Each partition has its own console.

To disable data prefetch on a HP SuperDome system, you must disable the prefetch option in each partition on which the Oracle server is running. To disable the prefetch option for each partition:

Telnet to the SuperDome system:

$ telnet superdome_hostname


The Guardian Server Processor (GSP) prompt appears.

At the prompts, enter your GSP username and password.

At the GSP prompt, enter the following command to access the Consoles menu:

GSP> CO


At the prompt, enter the number of the partition running the Oracle server.

The partition console appears.

Respond to the prompts that appear.

Log in to UNIX as the root user.

Enter the following command to determine the partition hostname:

# hostname


Enter the following command to reboot the partition:

# shutdown -r


The following message appears:

To discontinue boot, hit space bar within 10 secs....


Press the space bar within ten seconds to display the Boot Console Handler (BCH) menu.



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Note:
If you do not press the space bar within ten seconds, the partition reboots and you cannot access the BCH menu. If this happens, you must repeat steps 6 through 8.

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At the BCH menu prompt, enter CO to display the BCH Configuration menu.

At the Configuration Menu prompt, enter the following command:

DataPrefetch DISABLE


In UNIX, enter the following command to reboot the partition:

# shutdown -r


The following message appears:

To discontinue boot, hit space bar within 10 secs....


Ignore this message and allow the partition to reboot completely.

After the partition reboots, enter exit to exit the partition.

To disable data prefetch on another partition where the Oracle server is running, perform steps 4 through 14.


Regards,
David de Beer.