8.1.8 Database Portability

There are two fundamental approaches to making your DL/I databases available to IMS/ESA. One is to unload the database using DL/I utilities and reload it using IMS/ESA utilities. The other is to ²position² your DL/I databases using DL/I and IMS/ESA compatibility options in the DBD during a normal database reorganization under DL/I.

Since database reorganization involves considerable processing for large and complex databases, ²positioning² may offer some advantages. It can reduce the time required to actually switch the production applications from VSE to MVS. It can also allow alternate, not concurrent, access to the database by DL/I and IMS/ESA applications. Both approaches are described below.

8.1.8.1 Alternate DL/I and IMS/ESA Access

A database may be alternately accessed by VSE and MVS if the physical organization meets certain restrictions and compatibility options are specified in the appropriate DBDs. This allows IMS/ESA to access and update a DL/I database. However, the database must be initially unloaded and reloaded using DL/I utilities. If any reorganization is desired, this must also be performed under DL/I. IMS/ESA utilities may be used to make IMS image copies, merge IMS log tapes and execute IMS backout or forward recovery operations. Note that the image copy tapes, change accumulation tapes, or logs are not portable between DL/I and IMS/ESA.

To establish this environment, compatibility options must be used.

1.Unload the database using the VSE DL/I utility.

2.Identify and resolve any VSE VSAM incompatibilities as described in 5.6, ªVSAM Differencesº on page 110.

3.Specify IMSCOMP=YES in the DL/I DBDs describing the data portions of the database. Note that changes to the VSAM logical record sizes will be required. These are identified during the DBD generation.

4.Regenerate the DBDs and ACBs in VSE.

5.Reload the database using the appropriate VSE DL/I utility. The database may now be accessed by VSE applications again.

6.Specify DOSCOMP in the IMS/ESA DBDs describing primary or secondary index portions of the database.

7.Generate the IMS/ESA DBDs under MVS. The database is now accessible by IMS/ESA whenever the VSAM user catalog defining it has been disconnected from VSE and connected to MVS.

The database must be on a compatible VSAM supported device such as 3380, 3350 or 3375. FBA devices such as 3310 and 3370 are not supported by MVS.

When running in compatibility mode make sure the IMS/ESA and DL/I DBD definitions are kept in synchronization. Do this by explicitly defining parameters rather than letting them default. For example, CI size and record length for IMS/ESA should be defined to be the same as the DL/l values.

Once migration is complete the DOSCOMP parameter may be removed when the database is reorganized using the IMS/ESA utilities. There is no need to unload under DL/I and reload under IMS/ESA in this case.

Chapter 8. Databases 175

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IBM OS/390 manual Database Portability, Alternate DL/I and IMS/ESA Access

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.