SUMMARY OF MODIFICATONS AND ENHANCEMENTS V8.0

SINGLE SYSTEM RECORD LEVEL SHARING

IAM Version 8.0 introduces the first phase of IAM Record Level Sharing (RLS) support, which features single system record level sharing capabilities. Customers can use IAM Record Level Sharing to run multiple batch jobs and CICS regions that concurrently update the same IAM enhanced format file(s) on a single z/OS or OS/390 system image. IAM RLS provides full data integrity for concurrent users of IAM files under IAM RLS control, along with journaling and file recovery capabilities. Locking is provided at the record level by IAM RLS, to prevent concurrent updating of the same record by different jobs or CICS transactions. For most applications, no JCL or programming changes will be necessary to use IAM RLS. Some of the key features of IAM RLS are:

• Record level locking across multiple jobs and CICS regions on the same z/OS image

• Provides journaling and recovery capabilities

• Automatic deadlock detection, within the realm of locks held for IAM datasets

• Supports enhanced format IAM KSDS and ESDS files

• Datasets are selected automatically for inclusion in IAM RLS, based on the file's share options and / or on installation provided list of dataset names

• Offers a batch syncpoint process for batch applications that update a substantial portion of IAM files. (Requires changes to the application program to use this facility.)

• Provides an optional Dynamic Job Backout facility, which will backout updates made to IAM files being processed under IAM RLS control, when a batch job step abends.

• Customers can select the action that IAM RLS will take when there is record lock contention.

  The choices are to wait until the lock is available, wait for a specified amount of time, or to immediately fail the request. If the request is failed, customers can select to either receive VSAM logical error codes and have the application programs handle the error, or request that IAM abend the job step or transaction.

Full Sysplex record level sharing capabilities for IAM files will be available in a future release.

LARGE DEVICE SUPPORT IAM Version 8.0 provides support for IAM enhanced format datasets being defined as DFSMS extended format sequential datasets. These IAM datasets can now exceed the 64K tracks per device limitation that previously existed, allowing IAM to fully utilize 3390-9 and other even larger devices. When defined as DFSMS extended format, IAM datasets can use up to 123 extents per volume, can use all available space on the large volumes, and can exceed the prior limit of a total of 255 extents when multiple volumes are specified. This will raise the theoretical maximum file size to almost 3 terabytes of compressed data.

HARDWARE COMPRESSION SUPPORT IAM Version 8.0 provides customers with the option of using the z/OS hardware compression. With the performance improvements that IBM has made on the data compression instructions on the zSeries processors, IAM customers may realize some CPU time reductions when reading data by using hardware compression. The use of hardware compression is not recommended on the older processors, because the additional CPU time is substantial. Hardware compression is an option that users can select for the desired files through the IAM Override facility. IAM is providing one compression dictionary, which was designed to handle primarily text data, with some numerical data, such as might be found in files containing name and address information. Users can also create their own compression dictionaries to be used by IAM for selected files. Such dictionaries can provide for a higher degree of compression than would be possible with a generic dictionary. Instructions are provided in the manual for creating a hardware compression dictionary that can be used by IAM. When an IAM file is loaded with a user provided compression dictionary, that dictionary will be written into the IAM file to insure that the dataset can be successfully processed should some subsequent changes be made to the user provided dictionary.

PAV SUPPORT IAM Version 8.0 provides full Parallel Access Volume (PAV) support for enhanced format IAM files. PAV is a feature of some DASD devices, which provides for concurrent physical I/O activity against the same physical z/OS DASD volume. Use of this capability can provide for substantial improvements in response times for online systems, or batch jobs, that have heavy concurrent I/O activity. Prior to IAM Version 8.0, parallel access was automatically being handled for input requests to IAM files, but concurrent output I/O requests would only be concurrently processed if the requests were to different DASD extents. With Version 8.0, changes have been made to the IAM I/O driver for enhanced format files that will facilitate concurrent output and update I/O through PAV.

BWO SUPPORT IAM Version 8.0 provides support for users of the callable BWO (Backup While Open) service. This interface is primarily used by CICS and CICS/VR to allow for backing up open VSAM files, and then for subsequent forward recovery by CICS/VR after the dataset has been restored. IAM will now keep the BWO data in the IAM file's control information. The BWO data includes three flags, indicating the BWO state of the file, and the 8-byte date and time stamp field. The date and time stamp field is used as a file recovery starting point in time by CICS/VR when recovering a dataset that has been restored. When present in an IAM file, the BWO data will be printed on the IAMPRINT LISTCAT report.

IAM files could previously be backed up while open, and the restored copy would retain file structure integrity. However, now with the IAM BWO support, the forward recovery function can automatically determine the point in time from which the recovery should start. In effect, IAM BWO callable service support allows for the recovery coordination between CICS and CICS/VR.

IAM JOURNAL RECOVERY IAMJREST is the IAM program that will read data from an IAM journal, and perform the requested recovery. For V8.0, this program has been enhanced to handle the journal datasets produced by IAMRLS, and perform either a forward or backward recovery, as requested. This enhancement includes new keywords and functionality for recovering files after abends or failures when such files are used under IAM RLS. If a batch job abends, the IAM datasets that have been accessed through IAM RLS, can have the changes removed from the IAM file by a process referred to as a backout. The backout can be for only the failing job step, for the entire job, or also for other preceding jobs. If the failing program makes use of the IAM Batch Syncpoint, the back out can be done up to the last syncpoint taken prior to the abend.

Also note that all of the utility functions previously performed by IAMJREST have been moved to a new program, called IAMJUTIL. IAMJREST will only handle the actual recovery. To print journal records, find out information from journal records, or resetting the System Logger files, IAMJUTIL can be used.

AIX USEABILITY ENHANCEMENT Many users of IAM/AIX have been taking instant backups or snapshot copies of IAM base clusters without the alternate indices or paths. This has caused some various problems because the IAM AIX information is still in the copied base cluster. With V8.0, the IAM/AIX alternate index information can be removed from the copied base cluster through an IDCAMS delete command that specifies the copied base cluster name, and the keywords AIX and NOSCRATCH. A subsequent LISTCAT on the file will verify the removal of the AIX relationships from the base cluster.

Z-SERIES PROCESSORS IAM Version 8.0 has modified various portions of code that may have been adversely impacted by changes in the cache structure on the IBM Z-series processors. This may result in some CPU time reductions for customers upgrading from prior releases of IAM. The modifications were made in such a manner as to not degrade IAM performance for customers on the prior IBM mainframe processors.

VSAM QUICK INDEX The VSAM Quick Index from EMC (formerly Softworks) can be used with IAM alternate indexes starting with V8.0 of IAM. VSAM Quick Index must be run either defaulting to, or explicitly specified on the BASE control card, the NOFASTPATH option. Customers that are going to have both V7.0 and V8.0 of IAM active on the same LPAR during the V8.0 test period must apply PTF P-70.0150 to their V7.0 IAM to use VSAM Quick Index with IAM V8.0.

IAM ALTERNATE INDEX PERFORMANCE AIX PERFORMANCE As can be seen from the example data provided below, IAM can provide significant performance benefits over using VSAM. The performance benefits of using IAM for any particular application will vary from the results shown here, as there are many variables. Such variables include the number of upgradeable alternate index datasets, the data reference pattern, the amount of VSAM tuning that has been done, plus many others. The jobs were run on a Z800-2066 CPU under z/OS 1.3. The following numbers are from a base cluster with 2,500,000 records with two upgradeable alternate index datasets. One of the alternate index datasets has UNIQUE keys, the other has NONUNIQUE keys, and both were upgradeable. All of the measurements were done with minimal other activity on the system.

The IAM run was performed with the default options and the following buffer overrides:

ACCESS DD=&ALLDD,MINBUFNO=60,MAXBUFNO=100