Create Shared-Memory Portions

The database server uses the configuration values to calculate the required size of the database server resident shared memory. In addition, the database server computes additional configuration requirements from internal values. Space requirements for overhead are calculated and stored.

To create shared memory, the database server acquires the shared-memory space from the operating system for three different types of memory:

• Resident portion, used for data buffers, buffer tables, and so on
• Virtual portion, used for most internal and user-session memory requirements
• IPC communication portion, used for IPC communication

  The database server allocates this portion of shared memory only if you configure an IPC shared-memory connection.

Next, the database server attaches shared-memory segments to its virtual address space and initializes shared-memory structures. For more information about shared-memory structures, refer to Virtual Portion of Shared Memory.

After initialization is complete and the database server is running, it can create additional shared-memory segments as needed. The database server creates segments in increments of the page size.