With the shared pages function, which is available through the
IARVSERV macro, you can define virtual storage areas through which
data can be shared by programs within or between address spaces or
data spaces. Also, the type of storage access can be changed.
Sharing reduces the amount of processor storage required and the
I/O necessary to support data applications that require access to
the same data. For example, IARVSERV provides a way for a program
running below 16 megabytes, in 24-bit addressing mode, to access data
above 16 megabytes that it shares with 31-bit mode programs. IARVSERV
allows the sharing of data without the central storage constraints
and processor overhead of other existing methods of sharing data.
The sharing of data benefits many types of applications, because
data is available to all sharing applications with no increase in
storage usage. This function is useful for applications in either
a sysplex environment or a single-system environment. Additionally,
IARVSERV allows you to control whether a sharing program:
- Has read access only
- Has both read and write access and receives updates immediately
- Can modify the data without modifying the original, and without
allowing the sharing programs to view the updates
- Can modify the original while sharing programs see the change,
but without allowing the sharing programs to change the data
- Can change the current storage access
An additional macro, IARR2V, is provided as an aid to converting
central storage addresses to virtual storage addresses. See Converting a central to virtual storage address (IARR2V macro) for information on the IARR2V macro.
The IARVSERV topics described in this chapter are:
- Understanding the concepts of sharing data with IARVSERV
- Storage you can use with IARVSERV
- Obtaining storage for the source and target
- Defining storage for sharing data and access
- Changing storage access
- How to share and unshare data
- Accessing data in a sharing group
- Example of sharing storage with IARVSERV
- Use with data-in-virtual (DIV macro)
- Diagnosing problems with shared data
For coding information about the IARVSERV and IARR2V macros, see z/OS MVS Programming: Assembler Services Reference IAR-XCT.