gtpc3m20Concepts and Structures

Database Utilities

A large volume of application data records organized to enhance performance are usually characteristics of a TPF environment. These characteristics dictate the need for special support programs that are often referred to as database utilities.

Database utilities provide a variety of functions:

While most of these utilities are run on a regular basis, the utilities used in the initialization process are generally run only once (to generate the system) or very rarely (when the system definition requires change).

Generally, utilities are run during periods of low system activity and, in a loosely coupled environment, on only one CPC. They are also sensitive to subsystems and subsystem users.

The complexities of multiprocessing and MDBF are ignored in this conceptual description of the database utilities.

File Capture and Restore

The constant availability of the online data increases the exposure of file storage to the effects of software and hardware malfunctions. This exposure is minimized by ensuring that critical data can be replaced if necessary.

Maintenance of copies of file storage on auxiliary storage media (such as other module devices and magnetic tape) helps to protect against the loss of critical data. The process of copying file storage to auxiliary storage is called file capture or simply capture, and the process of restoring the data to the file storage is called restore.

The TPF system provides the ability to tailor the restoration of data to the severity of the loss of data. A full restore restores all file storage, whereas a partial restore restores one or more devices. Partial restores occur more frequently than full restores. The principal reason for a partial restore is the physical destruction of the data on a module.

The TPF system provides an online capture facility that captures data records during normal system operation, but during periods of low activity. Each file storage device is copied to magnetic tape. Simultaneously, a separate tape, called an exception tape, collects a copy of all records modified after they have already been captured. The combination of these two sets of tapes (capture tapes and exception tapes) is a total representation of the database at the instant that the online capture completes.

By the very nature of its function, the capture utility places very high demands on module resources, which impacts TPF system performance. To avoid over utilization of a group of channel paths or control units, the capture utility performs load balancing based on limits specified by the user installation. This minimizes the impact that this utility has on the I/O throughput of a TPF system.

Full restoration of a system brings the system back to the date and time of the capture completion. Additional programs or procedures may be required to reconstruct the file activity that occurred between the time of capture and the time of restoration. Because the data is application dependent, the additional reconstruction is an application function.

Database Reorganization

Normal system growth usually dictates an increase in the number of file storage devices. The addition of new devices provides an increase in both fixed and pool areas. While the pseudo module support, dispensing techniques, and directory maintenance used for the pool addresses permit the temporary addition of devices to the pool area, a database reorganization is required for the expansion of the fixed area and for permanent expansion to the pool area.

The expansion of the file area is accomplished by a TPF system utility called database reorganization. The database reorganization program collects all records using the record types and ordinal numbers of the current system definition. These records are then written into the new database configuration by using a new FACE table definition. Because of FARF, a database reorganization is transparent to application programs.

Figure 49 shows an example of reorganizing a database from three devices to four devices. Notice that the physical location of each record is changed while the numerical sequence of the records is retained. Records 10 and 11 are highlighted.

Figure 49. Database Reorganization


File Copy

The TPF system provides the file copy utility as a means of maintaining the module hardware devices by duplicating and replacing in-use modules during system operation. Therefore, the TPF objective of high availability is maintained.

This utility can:

Although the utility is designed for maximum efficiency, TPF system performance is adversely impacted because of the high demand on the module control units needed for the two modules used by the utility.

In a loosely coupled complex, the copy process is synchronized across the CPCs using XLF.

File Recoup

Occasionally, application programs may fail to return long-term pool addresses to the system, in which case the records are lost for further application usage. This causes the amount of available long-term pool records to be diminished and, if left unchecked, would result in pool depletion. Correcting application errors reduces this problem. Additionally, whenever the TPF system experiences a catastrophic error, some Entries may be partially processed. After a system restart, the TPF system, in order to guarantee data integrity, throws away a pre-defined amount of long-term pool addresses, which are never returned.

The file recoup utility is provided to recover usable long-term pool addresses. These lost addresses are made available to the system for subsequent reuse. The file recoup utility interfaces closely with the application environment to determine which long-term pool addresses are validly in use. A by-product of the file recoup utility is information that identifies application programs which may have lost long-term pool addresses.

Long-term pool addresses are lost in the following ways:

File recoup reconciles the long-term file pool directories with the actual status of the pool area, and in so doing, provides error summaries that can be used to isolate the causes of directory discrepancies. The file recoup program must access every fixed record and main storage table that can reference a pool record or a chain of pool records. The data gathered during this record accessing and chain-chasing phase is then used to create file pool directories that reflect the actual status of the file pool area. These reconstructed directories in which lost addresses have been recovered (recouped) are called pseudo directories. A pseudo directory is an accurate account of the long-term pool addresses at a discrete instant of time.

For more information about file recoup, see TPF Database Reference.

Pool Directory Generation and Maintenance

Use the ZPOOL GENERATION command to create new directory records or change existing directory records to conform to a changed file layout. For more information about the ZPOOL GENERATION command, see TPF Operations. For more information about file pool procedures, see TPF Database Reference.