Memory Requirements

Memory is used for a number of distinct tasks by any database application, including Oracle Internet Directory. If memory resources are insufficient for any of these tasks, then the CPUs work less efficiently and system performance drops. Furthermore, memory usage increases in proportion to the number of concurrent connections to the database and the number of concurrent users of the directory. For the purposes of capacity planning, an active connection begins when a client seeks to bind to the directory and ends when that bind is terminated.

The memory available to processes comes from the virtual memory on the system, which is somewhat more than available physical memory. If the sum of all active memory usage exceeds the available physical memory on the system, the operating system may need to store some of the memory pages on disk. This is called paging. Paging can degrade performance if memory is too oversubscribed. Generally, you should not exceed 20 percent over-subscription of physical memory. If paging occurs, you need either to scale back memory usage by processes or to add more physical memory. Keep in mind the trade-offs: There are physical limits to the amount of memory you can add, but scaling back on memory usage for each process can significantly degrade performance.

The main consumers of memory are the database buffer cache within the system global area (SGA) and the OID Server Entry Cache (if enabled). Getting a good hit ratio for the buffer cache and the entry cache requires allocating enough memory in each area. The following formula gives a rough estimate for the amount of RAM required to cache 'N' entries in the entry cache:

N * [ 150+ {attrs_per_entry + 6) * (avg_attrname_len + avg_attr_size + 40) } ]
* 1.3

See Also: Chapter 21, "Tuning Considerations for the Directory" for further information on SGA tuning

The following table gives minimum memory requirements for different directory configurations:

Table 20-11  Minimum Memory Requirements for Different Directory Configurations

Directory Type	Entry Count	Minimum Memory
Small	Less than 600,000	512 MB
Medium	600,000 to 2,000,000	1 GB
Large	Greater than 2,000,000	2 GB

Going back to our example of Acme Corporation, the number of entries in the directory are close to 1,000,000 (1 million). Oracle Corporation recommends choosing the 2 GB option in order to maximize performance.