Checkpoint-Restart in PL/I Plickpt, Plirest

15.5.2.9 SORT TECHNIQUES

The user can specify a particular sort technique:

PEER Peerage sort

BALN Balanced

CRCX Criss-cross

OSCL Oscillating

POLY Polyphase

The sort call is, therefore, little different to that of DOS PL/I. In all cases, reading the Programmers′ Guide for the appropriate version of the sort is recommended.

15.6 Checkpoint-Restart in PL/I

15.6.1 PLICKPT

Whereas the DOS checkpoint authorizes only manual restart with operator intervention, in MVS it is possible to request it by means of JCL and if the program lends itself to automatic restart, it will restart at the last step or the last checkpoint.

There are always four parameters to be supplied:

CALL PLICKPT (pl,p2,p3,p4); (DOS and MVS)

but the third has functional differences. In DOS the parameter defines the physical and logical unit on which the checkpoints will be written (SYS00x..,33xx). In MVS this defines the checkpoint organization (sequential or partitioned). For the other parameters, there is little or no difference:

P1: DLBL in DOS, DDNAME in MVS.

P2: Name to be given to the checkpoint by the operating system. This name will be specified in control statement on a deferred restart.

P4: Return code returned by the checkpoint routines after execution. The values of these return codes are compatible between the two compilers.

15.6.2 PLIREST

An additional function offered by MVS is available in PL/I; automatic restart. This is possible thanks to a new function of the MVS PL/I optimizer: PLIREST. This includes use of ABEND U4092. As long as this code is in the list of eligible ABEND codes specified at system generation, an automatic restart will be possible. If there is to be automatic restart, the operating system must be able to recognize an abnormal end. With PL/I intercepting program checks, the end of execution appears to the system as ′normal′. Thus the function of PLIREST is to induce an ABEND. It is, therefore. necessary to code some instructions of the type:

IF ONCODE= xxx THEN DO;

...........:

CALL PLIREST; END;

On restart, control will be returned to PL/I after the instruction CALL PLICKPT

(.......). On testing the return code, the programmer will be able to tell if he has a

restart or after writing a checkpoint.

342VSE to OS/390 Migration Workbook

OS/390 specifications

IBM OS/390, a versatile operating system, was a cornerstone in enterprise environments and played a pivotal role in mainframe computing. Released in the mid-1990s, OS/390 combined the strengths of IBM's MVS (Multiple Virtual Storage) with new features and enhancements, targeting scalability, reliability, and performance in demanding business applications.

One of the key features of OS/390 was its robust support for multiple users and processes. The system allowed thousands of concurrent users to access applications and data, ensuring high availability and minimizing downtime—a critical requirement for many large organizations. This scalability was supported through various enhancements in memory management and processor scheduling, enabling optimal resource allocation across diverse workloads.

OS/390 was known for its superior workload management capabilities. The Workload Manager (WLM) component allowed administrators to define service policies, specifying how system resources would be allocated according to the priority of tasks. This ensured that critical business processes received the necessary resources while less critical tasks were managed more flexibly.

Another significant characteristic of OS/390 was its commitment to security. The operating system provided comprehensive security features, including user authentication, data encryption, and auditing capabilities. This focus on security was vital for organizations handling sensitive data, ensuring compliance with regulations and safeguarding against unauthorized access.

OS/390 also supported advanced technologies that facilitated integration and development. The system included features like the IBM CICS (Customer Information Control System) for transaction processing and IMS (Information Management System) for database management. These technologies allowed organizations to build robust, high-performance applications tailored to specific business needs.

The ease of network integration was another strength of OS/390. With the advent of the Internet and global connectivity, OS/390 systems could easily interface with various network protocols, enabling businesses to operate in a connected world. This inclusion paved the way for many organizations to expand their capabilities and offer new services, driving digital transformation.

In conclusion, IBM OS/390 represented a significant advancement in mainframe technology, combining scalability, security, and robust workload management. Its rich feature set and support for critical enterprise applications solidified its role as a vital component of many organizations' IT infrastructures, ensuring they could meet their operational challenges head-on while supporting future growth. As technology continues to evolve, the legacy of OS/390 remains influential in the realm of computing.

IBM OS/390 Checkpoint-Restart in PL/I Plickpt, Plirest, Call Plickpt pl,p2,p3,p4 DOS and MVS

Models: OS/390