Shared Memory

Shared memory is an operating-system feature that allows the database server threads and processes to share data by sharing access to pools of memory. The database server uses shared memory for the following purposes:

• To reduce memory usage and disk I/O
• To perform high-speed communication between processes

Shared memory enables the database server to reduce overall memory uses because the participating processes, in this case, virtual processors, do not need to maintain private copies of the data that is in shared memory.

Shared memory reduces disk I/O because buffers, which are managed as a common pool, are flushed on a database server-wide basis instead of a per-process basis. Furthermore, a virtual processor can often avoid reading data from disk because the data is already in shared memory as a result of an earlier read operation. The reduction in disk I/O reduces execution time.

Shared memory provides the fastest method of interprocess communication because it processes read and write messages at the speed of memory transfers.