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Lesson 3OS memory management
ObjectiveExplain UNIX memory management

Explain UNIX memory management

The UNIX operating system is designed to manage memory structures to maximize the memory usage. UNIX rules depend upon both OS parameters and Oracle memory parameters. The systems administrator is required to define a swap disk in all UNIX environments. The swap disk temporarily holds memory segments that must be paged-out from UNIX to make room for incoming memory requirements.—The swap disk is a component of the virtual memory, that memory in excess of the physical RAM memory capacity of the database server. To better understand how the swap disk functions, examine the following Slide Show.
Swap Disk1
1) Swap Disk1
Swap Disk2
2) Swap Disk2
Swap Disk3
3) Swap Disk3
Swap Disk4
4) Swap Disk4
Swap Disk5
5) Swap Disk5

Here we see the basic constructs of virtual memory management. While it is common for all OS systems to page-out unreferenced memory, the page-in operations are of concern because they slow down the process.

Swap disk data

To display the amount of swap disk defined on your server and how much has been used, use the following UNIX command:
diogenes:> lsps –s

Total Paging Space   Percent Used

512MB              35%

While we are using UNIX in these lessons, the same virtual memory principles apply to all Oracle servers, including NT servers and IBM mainframes. In fact, the common mainframe MVS/ESA stands for Multiple Virtual Storage/Extended Storage Architecture. The next lesson looks at a common UNIX utility for detecting memory paging.

OS Memory Management - Exercise

Before moving on to the next lesson, click the Exercise link to assess your overall understanding of virtual memory with the following matching exercise.
OS Memory Management - Exercise