Abstract: Segments of storage of a computer system are shared among any number of users at varying virtual addresses. The virtual addresses can be in the same address space or different address spaces. The sharing of a segment of storage is provided by storing the real address of a page table corresponding to the segment of storage to be shared at different virtual addresses. This allows users of the same or different address spaces to share the same segment of storage by referencing the same page table.

Abstract: An indicator is provided in a Page Frame Table Entry to identify a page frame as “Permanently Non-Preferred” (PNP). The indicator is set for page frames in storage subincrements which have locations corresponding to page frames determined to be “bad” (permanent errors) during system IPL, when reconfiguring storage on-line, or when a storage-related error occurs for such a frame during system execution. Mechanisms are provided to convert even PNP page frames to preferred status when shortages of preferred pages exist; but the mechanism used for choosing PNP frames, and for determining which PNP frames to convert to preferred status when conversion is needed, increase the likelihood of locating a target subincrement to use in copying pages from a preferred storage subincrement when the preferred storage is taken off-line.

Abstract: A multisystem log stream of a multisystem environment is compressed. The oldest record needed for each system that can write or delete entries from the multisystem log stream is tracked, and that information is used in compression of the log stream. The block ids associated with those oldest records are maintained within a vector, and when the vector is updated, a determination is made as to whether the entry in the vector that it replaced previously contained the lowest block id in the vector. If so, all the records having block ids lower than the new lowest block id in the vector are deleted.

Abstract: One system of a multisystem environment takes over log entries owned by another system of the environment. When a system owning entries on a primary log stream is inactive (or a sync point manager on the system is inactive), another system of the multisystem environment writes the log entries corresponding to the inactive system to other locations. The entries within the other locations are not owned by any system. Thus, the resource managers associated with those log entries are eligible for restarting on any system of the multisystem environment. However, all resource managers involved in a common set of transactions are to restart on the same system. The other resource managers can restart on another system. When one of the resource managers restarts on a system, the system takes back ownership of the entries associated with the common set of transactions.

Abstract: One system of a multisystem environment takes over log entries owned by another system of the environment. When a system owning entries on a primary log stream is inactive (or a sync point manager on the system is inactive), another system of the multisystem environment writes the log entries corresponding to the inactive system to other locations. The entries within the other locations are not owned by any system. Thus, the resource managers associated with those log entries are eligible for restarting on any system of the multisystem environment. However, all resource managers involved in a common set of transactions are to restart on the same system. The other resource managers can restart on another system. When one of the resource managers restarts on a system, the system takes back ownership of the entries associated with the common set of transactions.

Abstract: A multisystem log stream of a multisystem environment is compressed. The oldest record needed for each system that can write or delete entries from the multisystem log stream is tracked, and that information is used in compression of the log stream. The block ids associated with those oldest records are maintained within a vector, and when the vector is updated, a determination is made as to whether the entry in the vector that it replaced previously contained the lowest block id in the vector. If so, all the records having block ids lower than the new lowest block id in the vector are deleted.

Abstract: The amount of real memory space used by descriptor tables of a computer system is reduced. On system initialization, sufficient contiguous virtual memory space for each table is allotted for descriptors in the tables to define all memory space in both central storage and expanded storage. However, only descriptors for on-line storage locations, relative to a particular partition, are placed in these tables. As the system operates, the tables are continuously updated, removing descriptors for storage locations taken off-line and adding descriptors for blocks of memory brought on-line so that the tables reflect only the storage locations then on-line in the particular partition.