D Administering Oracle Database on HP-UX

D.2.1 Enabling SCHED_NOAGE for Oracle Database

To permit Oracle Database to use the SCHED_NOAGE scheduling policy, the OSDBA group (typically, the dba group) must have the RTSCHED and RTPRIO privileges to change the scheduling policy and set the priority level for Oracle processes. To give the dba group these privileges:

1. Log in as the root user.

2. Using any text editor, open the /etc/privgroup file, or create it if necessary.

3. Add or edit the following line, which begins with the name of the OSDBA group, specifying the privileges RTPRIO and RTSCHED that you want to grant to this group every time the system restarts:

   dba RTPRIO RTSCHED
   

4. Save the file, and quit the text editor.

5. Enter the following command to grant the privileges to the OSDBA group:

   # /usr/sbin/setprivgrp -f /etc/privgroup
   

6. Enter the following command to verify that the privileges are set correctly:

   # /usr/bin/getprivgrp dba
   

Add the HPUX_SCHED_NOAGE initialization parameter to the parameter file for each instance, setting the parameter to an integer value to specify process priority levels. The supported range of values is 178 to 255. Lower values represent higher priorities. The default value of HPUX_SCHED_NOAGE initialization parameter is 178 for all Oracle processes. For LMS processes, this can be changed by setting the initialization parameter _os_sched_high_priority. If the parameter _os_sched_high_priority is between 31 and 2, LMS processes run with SCHED_RR at the set priority. If the parameter value is between 178 and 255, the processes run at the set value with SCHED_NOAGE. However, LMS does not run at priority level less than the value of HPUX_SCHED_NOAGE.

If the HPUX_SCHED_NOAGE parameter setting is out of range, then Oracle Database automatically sets the parameter to a permissible value and continues with the SCHED_NOAGE policy with the new value. It also generates a message in the alert_sid.log file about the new setting. Whenever the highest priority is assigned to Oracle processes, either by the user or by automatic readjustment, Oracle Database generates a message in the alert_sid.log file warning about the possibility of exhaustion of CPU resources on the system. Oracle recommends that you set the parameter to assign the priority level you want for Oracle processes.

D.4.1 Granting MLOCK Privilege

To permit Oracle Database to process asynchronous Input-Output operations, the OSDBA group (dba) must have the MLOCK privilege. To give the dba group the MLOCK privilege:

1. Log in as the root user.

2. Using any text editor, open the /etc/privgroup file, or create it if necessary.

3. Add or edit the following line, which begins with the name of the OSDBA group, specifying the privilege MLOCK:

   Note:

   You must use only one line to specify the privileges for a particular group in this file. If the file already contains a line for the dba group, then add the MLOCK privilege on the same line.

   dba RTPRIO RTSCHED MLOCK
   

4. Save the file, and quit the text editor.

5. Enter the following command to grant the privileges to the OSDBA group:

   # /usr/sbin/setprivgrp -f /etc/privgroup
   

6. Enter the following command to verify that the privileges are set correctly:

   # /usr/bin/getprivgrp dba
   

D.4.2 Implementing Asynchronous Input-Output

To use asynchronous Input-Output on HP-UX, you must use an Automatic Storage Management disk group that uses raw partitions as the storage option for database files.

Before you can implement asynchronous Input-Output with either storage option, you must use the System Administrator Management utility to configure the asynchronous disk driver into the HP-UX kernel.

To add the asynchronous disk driver and configure the kernel by using the System Administrator Management utility:

1. Run the following command as the root user:

   # sam
   

2. Select the Kernel Configuration area.

3. Select the Drivers area.

4. Select the asynchronous disk driver (asyncdsk).

5. Select Actions, and then select Add Driver to Kernel.

6. Select List, and then select Configurable Parameters.

7. Select the MAX_ASYNC_PORTS parameter.

8. Select Action, and then select Modify Configurable Parameter.

9. Specify a new value for the parameter, using the following guidelines, and then click OK.

   The MAX_ASYNC_PORTS parameter is a configurable HP-UX kernel parameter that controls the maximum number of processes that can open the /dev/async file simultaneously.

   The system displays an error message when a process tries to open the /dev/async file after the maximum number of processes have opened the file. This error can reduce performance on systems with a large number of shadow processes or many parallel query slaves performing asynchronous Input-Output. This error is not recorded. To avoid this error, estimate the highest likely number of processes that can access the /dev/async file and set the MAX_ASYNC_PORTS parameter to this value.

10. Select Actions, and then select Process a New Kernel.

11. Select one of the following options, and then click OK:

    • Move Kernel Into Place and Shutdown System/Reboot Now

    • Do Not Move Kernel Into Place: Do Not Shutdown/Reboot Now

    If you choose the second option, then the new kernel, vmunix_test, and the system.SAM configuration file used to create it, are both created in the /stand/build directory.

To enable asynchronous Input-Output operations using the HP-UX asynchronous device driver:

1. Log in as the root user.

2. If /dev/async does not exist, use the following command to create it:

   # /sbin/mknod /dev/async c 101 0x0
   

   By default, the minor number is set to 0. The following table describes the various minor numbers for 8-bit that you can use to create a device file:

   Minor number	Description
   0x0	This is the HP-UX default value for /dev/async.
   0x4	Enable disc device timeouts to complete with an error code rather than retrying forever. This setting is necessary for application-level disc mirroring, so as to avoid the situation where the application waits forever for a failed disc device to be repaired. Oracle RDBMS users should enable this feature when Automatic Storage Management mirroring/replication (internal redundancy) is used. SGA will be locked in memory.
   0x100	Enable on-demand locking of memory pages by async driver when asyncdsk_open(2) is called.   A low-overhead routine is then used to lock a page into memory during I/O operations. On-demand locking is critically important when using Oracle's Automatic Memory Management feature (the use of MEMORY_TARGET in the init.ora file to control memory usage). RDBMS deployments utilizing dynamic nPar or dynamic vPar features should also configure on-demand locking. More traditional RDBMS deployments can consider on-demand locking in light of its more obvious effects. Generally speaking, RDBMS startup will be quicker because the complete SGA is not locked into memory immediately. However, some instances will experience a slight run-time performance penalty with on-demand locking as memory pages are dynamically locked/unlocked for each I/O request.
   0x104	This is a combination of 0x100 and 0x4. Both the features are enabled.

   
   

3. Enter the following command to verify that the /dev/async device file exists and has the major number 101:

   # ls -l /dev/async
   

   The output of this command should look similar to the following:

   crw------- 1 oracle   dba     101 0x000000 Oct 28 10:32  /dev/async
   

4. If required, give the device file the operating system owner and permissions consistent with those of the Oracle software owner and OSDBA group.

   If the Oracle software owner is oracle and the OSDBA group is dba, then run the following commands:

   # /usr/bin/chown oracle:dba /dev/async
   # /usr/bin/chmod 660 /dev/async
   

D.4.3 Verifying Asynchronous Input-Output

To verify asynchronous Input-Output, first verify that the HP-UX asynchronous driver is configured for Oracle Database, then verify that Oracle Database is executing asynchronous Input-Output through the HP-UX device driver:

• Verifying That HP-UX Asynchronous Driver is Configured for Oracle Database

• Verifying that Oracle Database is Using Asynchronous Input-Output

D.4.4 Asynchronous Flag in SGA

Oracle Database on HP-UX uses a nonblocking polling facility provided by the HP-UX asynchronous driver to check the status of Input-Output operations. This polling is performed by checking a flag that is updated by the asynchronous driver based on the status of the Input-Output operations submitted. HP-UX requires that this flag be in shared memory.

Oracle Database configures an asynchronous flag in the SGA for each Oracle process. Oracle Database on HP-UX has a true asynchronous Input-Output mechanism where Input-Output requests can be issued even though some previously issued Input-Output operations are not complete. This helps to enhance performance and ensures good scalability of parallel Input-Output processes.

Releases of Oracle Database earlier than release 8.1.7 were able to run Input-Output operations only from shared memory by using the HP-UX asynchronous driver. Oracle Database 11g runs Input-Output operations from both shared memory and process-private regions using the new HP-UX asynchronous driver. However, Input-Output operations through the asynchronous driver are not asynchronous in nature. This is because Oracle Database must perform a blocking wait to check the status of Input-Output operations submitted to the asynchronous driver. This causes some Oracle processes, such as the database writer process, to essentially process synchronous Input-Output.

D.5.1 Default Large Virtual Memory Page Size

By default, Oracle Database uses the largest virtual memory page size setting available on HP-UX for allocating process-private memory. It is defined by the value L (largest.) This value is set as one of the LARGE_PAGE_FLAGS options when linking an Oracle executable.

When the virtual memory page size is set to L, HP-UX allocates the available process-private memory to pages of 1 MB, 4 MB, 16 MB and so on, until it reaches the 1 GB limit, or until it reaches the total amount of allocated memory. If you allocate enough memory to the Oracle PGA for the operating system to be able to allocate memory in larger data page size units, then the operating system allocates the maximum page size at once. For example, if you allocate 48 MB for the Oracle PGA, then the system can have either 3 pages each of 16 MB, or a series of pages in unit sizes with the smaller multiples. For example, four 1 MB pages, three 4 MB pages, and two 16 MB pages. If you allocate 64 MB to the PGA, then the operating system allocates one page of 64 MB, as the data page unit size matches the available memory.

In general, large memory pages yield better application performance by reducing the number of virtual memory translation faults that must be handled by the operating system, freeing more CPU resources for the application. Large pages help to reduce the total number of data pages required to allocate the process-private memory. This reduction decreases the chances of translation lookaside buffer misses at the processor level.

However, if applications are constrained in memory and tend to run a very large number of processes, then this drastic page size increase may lead processes to indicate large memory allocations, followed by an Out of memory error message. If this happens, then you must lower the page size to a value between the D (default) size of 4 KB and the L (largest) size of 4 GB.

With the lowest page size setting (4 KB), CPU utilization can be 20 percent higher than that with a larger page size setting. With the highest setting of L, the memory utilization can be 50 percent higher than that with a 4 MB setting. In cases where the system shows memory constraints, Oracle recommends that you set the page size to match the requirements of the particular application, within the constraints of available memory resources.

For example, an application that has problems with the L setting may show reasonable performance with a 4 MB virtual memory page setting.

D.5.2 Tuning Recommendations

To address tuning for the increased memory allocation required for persistent private SQL areas and large virtual memory page sizes, Oracle recommends that you decrease the virtual memory data page size for Oracle Database as required. Use the following command to alter the page size setting:

# /usr/bin/chatr +pd newsize $ORACLE_HOME/bin/oracle

In the preceding example, newsize represents the new value of the virtual memory page size.

Display the new setting using the chatr command as follows:

# /usr/bin/chatr $ORACLE_HOME/bin/oracle

D.5.3 Tunable Base Page Size

A large base page size enables efficient memory management. The default value for base_pagesize is 4 KB. The new feature introduced with HP-UX 11.31 enables to adjust the size of the base page, by invoking kctune (1 M) to change the tunable base_pagesize and then restart the computer.