What does IMS High Performance Unload do?
IMS High Performance Unload includes two unload utilities, FABHURG1 and FABHFSU, that provide high speed unloading capability. It also includes an application programming interface (API) for DL/I application programs that use GN calls.
As processing volumes increase, more work needs to be done in a shorter time due to shrinking batch windows. IMS High Performance Unload saves you time and money by reducing the CPU and elapsed time that is required to unload IMS databases and to run IMS data retrieval application programs. Powerful functions such as the ability to continue processing after a pointer error, a user exit facility, and various unloaded record formats are provided, all with the goal of improving availability and throughput.
IMS High Performance Unload is designed for use with IMS Database Reorganization Expert for z/OS® and IMS Online Reorganization Facility, as well as with other high performance IMS Tools products to provide the most efficient and powerful end-to-end solution for IMS database reorganization.
IMS High Performance Unload replaces the functionality of the IMS HD Reorganization Unload utility (DFSURGU0).
IMS High Performance Unload is serviced by a high-performance database retrieval engine called High Speed Sequential Retrieval (HSSR) Engine. IMS High Performance Unload also has an application programming interface (API) that is compatible with the HSSR call API provided by High Speed Sequential Retrieval of IMS System Utilities, Data Base Tools (PID: 5685-093).
Two unload utilities
IMS High Performance Unload provides two unload utilities; FABHURG1 and FABHFSU. Both utilities offer the following functions:
- Fast segment retrieval from databases
- The segment retrieval engine of IMS High Performance Unload, HSSR Engine, provides the facility to retrieve segments much faster than DL/I. See IMS High Performance Unload system structure.
- Unloading a database without decompressing compressed segments
- Both unload utilities can unload a database that uses the Segment Edit/Compression Exit without decompressing the segments. This method can decrease the CPU time and elapsed time. See the following topics to activate the decompress option:
- Unloading a selected partition or a selected sequence of partitions of a HALDB
- Both unload utilities support unloading of a HALDB. For details, see Methods for processing High Availability Large Databases.
- Ability to monitor the need for database reorganization by examining statistical reports
- The unload utilities can generate statistical reports that can be used for database tuning purposes. For details, see Obtaining statistics for database tuning.
- Ability to monitor the quality of HDAM or PHDAM randomizing by examining statistical reports
- The unload utilities can generate statistical reports that can be used to measure the quality of HDAM or PHDAM randomizing. For details, see Obtaining statistics for database tuning.
- Ability to continue processing after sequence errors
- HSSR Engine optionally
performs sequence-key checks for twin chains. You can select the behavior
for a sequence error from the following options:
- HSSR Engine gets to abend.
- HSSR Engine returns a GG status code and unloads neither the segment in error nor its dependents.
- HSSR Engine returns a GX status code and unloads the segment in error.
- Reading a corrupted database
- Options in IMS High Performance
Unload increases the control you have when you unload a database that
contains an incorrect pointer or incorrect HISAM records:
- Incorrect HD pointers can be bypassed.
- The processing of the remainder of the incorrect HISAM record can be skipped.
- The root segments of HIDAM or PHIDAM database can be accessed by use of the primary index, instead of traversing the root twin chain and the RAP chain.
For details, see Utility options for unloading corrupted databases.
Application programing interface
The application programming interface (API) of IMS High Performance Unload enables an IMS DL/I batch application program, which reads a database sequentially, to use HSSR Engine without being recompiled or relink-edited. The API enables DL/I application programs to use HSSR Engine to read a database by using GN calls. Through this API, the application program can retrieve a large number of segments more efficiently than the native IMS DL/I and the elapsed time and CPU time can be reduced.
Database organizations supported
IMS High Performance Unload supports the following database organizations:
- HDAM (Hierarchical Direct Access Method)
- HIDAM (Hierarchical Indexed Direct Access Method)
- PHDAM (Partitioned HDAM)
- PHIDAM (Partitioned HIDAM)
- HISAM (Hierarchical Indexed Sequential Access Method)
- SHISAM (Simple HISAM)
You can unload a partition or a sequence of partitions of a PHDAM or PHIDAM database.
Other database organizations are not supported by IMS High Performance Unload.
- Secondary index databases are supported, but are processed as independent databases. Processing of a partitioned secondary index is not supported.
- IMS/ESA® Partition Support Product for MVS/ESA (5697-A06) and IMS/ESA Partition Support Product for MVS/ESA Version 2 (5697-D85) are not supported.
Compatibility with prior products
IMS High Performance Unload is compatible with the following prior products:
- DBT V2 HSSR
- IMS System Utilities/Data Base Tools Version 2, High Speed Sequential Retrieval (5685-093)
- DBT V1 HSSR
- IMS System Utilities/Data Base Tools Version 1, High Speed Sequential Retrieval (5668-856)
- PO HSSR
- Program Offering High Speed Sequential Retrieval Version 2 (IFP 5787-LAC)
- FSU II
- IMS/VS Fast Scan Utility II Version 2 (FDP 5798-DFN)