CPU Usage Tuning

The CPU is perhaps the most important resource available for any software. While Chapter 20, "Capacity Planning for the Directory" gives a rough estimate of the required CPU horsepower for a given application load, sometimes insufficient tuning can cause inefficient use of the CPU resources. Consider tuning CPU resources if either of the following cases is true:

• At peak loads the CPU is 100 percent utilized.

• At peak loads the CPU is underutilized, there is a significant amount of idle time in the system, and this idle time cannot be eliminated at even higher loads.

Internal benchmarks show that Oracle Internet Directory performs best when approximately 70 to 75 percent of the CPU resources are consumed by Oracle Internet Directory processes, and the remaining (about 25 to 30 percent) are consumed by the Oracle foreground processes corresponding to the database connections. While monitoring CPU usage, it is also important to monitor the percentage of time spent in the system space compared to user space. Internal benchmarks show best throughput numbers at about 85 percent user and 15 percent system time.

This section contains these topics:

• Tuning CPU for Oracle Internet Directory Processes

• Tuning CPU for Oracle Foreground Processes

• Taking Advantage of Processor Affinity on SMP Systems

• Other Alternatives for a CPU Constrained System

Tuning CPU for Oracle Internet Directory Processes

The demands placed by Oracle Internet Directory processes on the CPU can be controlled by the ORCLSERVERPROCS and ORCLMAXCC parameters. This table lists suggested values for these parameters for various client loads:

ORCLSERVERPROCS	ORCLMAXCC	# Concurrent clients supported without degrading throughput of operations	# Clients supported without dropping connections	Required # of CPUs
1	2	40		1
2	10	400	800	2
4	10	800	1600	4
8	10	1600	3200	8

If we take the example of 500 concurrent clients, a value of 4 for ORCLSERVERPROCS with a value of 10 for ORCLMAXCC will result in the following configuration:

• There will be four server processes created.

• Each server process will spawn 10 worker threads that will do the actual work.

• Each server process will also maintain a pool of eleven database connections (10+1) that will be shared among the worker threads.

Oracle Internet Directory scales very well with CPU resources both with respect to the throughput of operations and concurrency of clients. From the previous table, say we have a 4 CPU box and are able to maintain a peak throughput of 'p' operations every second for a concurrency of 'n' clients.

With additional number of CPUs or with faster CPUs, we can achieve either or both of the following benefits:

• Achieve a thoughput higher than 'p' for the same concurrency of 'n' clients

• Maintain the same 'p' operations throughput for a concurrency higher than 'n'

If the CPU usage at peak loads is not at 100 percent and the system is idle for a large percentage of the time (that is, more than 5 percent), this indicates that Oracle Internet Directory processes are under-configured and are not making the best utilization of the CPU resources. To solve this problem, one must systematically increase the values of ORCLSERVERPROCS and ORCLMAXCC until the CPU utilization reaches 100 percent and the system and user time are split up as follows:

• User time: 85 percent or higher

• System time: 15 percent or lower

Tuning CPU for Oracle Foreground Processes

Tuning of CPU resources for Oracle Foreground processes should be considered only if both of the following conditions are met:

• The CPU usage is close to 100 percent at peak loads.

• Oracle foreground processes consume more than 30 percent of all available CPU resources.

If Oracle foreground processes are consuming excessive CPU, it implies that the queries that Oracle Internet Directory is making against the database are using too many CPU cycles. Although there is very little control available to the users on the types of underlying operations performed by the database, the following should be attempted:

• Database statistics on all of the tables and indexes associated with the ODS user on the database must be collected using the ANALYZE command. This helps the cost-based optimizer make better execution plans for the queries generated by Oracle Internet Directory. $ORACLE_HOME/ldap/admin/oidstats.sh can be used to collect statistics.

• If the ANALYZE fails to produce better results, and the LDAP queries used have a lot of filters in them, then a simple reorganization of the order in which the filters are specified (with the most specific filter in the beginning and the most generic filter at the end) helps reduce the CPU consumption of the Oracle foreground processes.

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Taking Advantage of Processor Affinity on SMP Systems

Several Symmetric Multi-Processor (SMP) systems offer the capability to bind a particular process to a particular CPU. While it is generally a good idea not to bind any process to any processor, it may improve performance if the following conditions are met:

• The CPU utilization of the entire system is close to 100 percent.

• There are more than two CPUs on the computer.

In internal benchmarks, it has been observed that binding the OID Server process and its associated Oracle shadow processes to the same CPU generally gives the best performance.

Other Alternatives for a CPU Constrained System

If none of the tips stated in the preceding sections solve CPU related performance problems, the following options are available:

• Upgrade the processing power of the computer, that is, add more CPUs or replace slower CPUs with faster ones.

• Keep the Oracle directory server and the associated Oracle9i database on separate computers.