EZ-Synchro/Share & XMVS

Full Integrity for Multiple CV IDMS Environments

EZ-Synchro & EZ-Share

EZ-Synchro and EZ-Share give CA-IDMS users far greater scope and flexibility in defining multiple CV environments by using MVS cross-memory services to synchronize the database buffers.

The Problem

CA-IDMS itself permits the sharing of areas between multiple CVs and local mode batch jobs with the restriction that only one at a time may READY an area for update processing. However, users who operate in this fashion will invariably suffer from undesirable side effects, namely inconsistent data and perceived broken chains. This is because of the manner in which CA-IDMS manages its buffer storage; Use of a stack for buffers ensures that frequently accessed database pages remain in memory without requiring disk access.

If an update process in another CV or batch job modifies a database page that is currently in memory in a retrieval CV, the retrieval CV will reference out-of-date data for an indeterminate time. Worse still, if an update process in another CV or batch job were to delete a set-member, the retrieval process could abend with a "broken-chain" error while walking the set.

The Solution

EZ-Synchro uses MVS cross-memory services to maintain buffer integrity and ensures these problems do not occur. Whenever a database page is updated, the buffers of other synchronized CA-IDMS jobs are searched for the existence of this page. If it is found, EZ-Synchro invalidates the page in the buffer, forcing a re-read of the page next time it is required.

Synchronization between CA-IDMS systems on different LPARs or machines is enabled with the EZ-XMVS (Cross-MVS) Option.

With the EZ-Share active, EZ-DB dataspaces are automatically shared between all concurrently executing CA-IDMS central version and local mode batch jobs.

In addition, by specifying a EZ-Share ShrdREAD Table, users may also share CA-IDMS DMCL buffer pools and CA-IDMS dataspaces . The ability to share dataspaces and DMCL buffer pools between multiple CA-IDMS services allows users to achieve optimum I/O rates for the minimum cost of virtual storage.

EZ-XMVS

Cross-MVS Option - EZ-Synchro Cross-MVS option is an extension to EZ-Synchro which permits database buffer synchronization to take place between CA-IDMS jobs executing on different physical processors. Standard EZ-Synchro achieves buffer synchronization between CA-IDMS jobs running on the same MVS system using cross-memory services. Cross-MVS option achieves buffer synchronization between CA-IDMS jobs running on different MVS systems using a combination of cross-memory services and LU6.2 (APPC).

Cross-MVS option permits users even greater flexibility in designing multi-central version environments by allowing exploitation of IBM's PR/SM and multi-cpu environments.

 

EZ-Synchro/Share Applications & Benefits

Performance and Throughput

Many sites operating large CA-IDMS systems find themselves CPU bound within a single processor and unable to exploit unused power available within other processors. CA-IDMS Multi-Processing (MP mode) often does not help (depending on contention for the different modes), and often the database/application design does not lend itself to segmentation techniques required to split the processing over multiple CVs.

Many sites have used the far simpler and more effective technique of splitting transactions over multiple update and read-only CVs. When the right balance of update and read transactions can be achieved, this technique gives unsurpassed levels of multiprocessing.

However, without EZ-Synchro®, this technique is susceptible to the types of errors described earlier (i.e. inconsistent data or perceived broken chains). Where CPU bottlenecks are the problem, it is usually a simple task to split the processing between update and retrieval transactions.

Many users of EZ-Synchro® are attaining transaction levels unobtainable in conventional CA-IDMS environments and have avoided costly upgrades.

Sharing of Areas

It is common for sites to have multiple CVs having retrieval only access to another CV's dictionary or to centralized reference or security data areas. Typically, reference data is the most likely to remain stuck in the buffers of the retrieval CVs hence providing inconsistent data to users. This is another example of the sort of problem that can be avoided with EZ-Synchro.

Local Mode Processing

It is common practice at some sites to VARY areas OFFLINE or to RETRIEVAL, while a local mode batch UPDATE process runs against the area. If the local mode job is executed under EZ-Synchro control, users accessing the area under CV will always have access to the most current data available, as EZ-Synchro will flush any pages from the CV buffers which have been updated by the local job.

Security Domains

The security system of CA-IDMS uses GLOBAL RESOURCES and SECURITY DOMAINS. The GLOBAL RESOURCES are USERS, GROUPS, USER PROFILES and SYSADMIN privileges. A SECURITY DOMAIN consists of all of the CA-IDMS services (batch jobs and central versions) that share the same physical user catalog (i.e., the SYSUSER segment).

Sharing these GLOBAL resources can greatly reduce the effort needed to maintain the security environment as there is no duplication of effort when adding new users, groups etc. Also, once a change is made to the shared SYSUSER segment, it will be reflected across all systems, thus eliminating possible inconsistences. But will the change be reflected IMMEDIATELY across all systems? It is possible that following an update to the SYSUSER segment, a CA-IDMS central version that has read only access to the SYSUSER segment will not pick up the change as the relevant database pages are still in the buffer pool and will therefore not be re-read from disk. This inconsistency might manifest in a new user signing on only to find that his user ID is not defined to the user catalog. Security administration quickly adds the user ID and the user attempts the signon once more. The relevant pages are still in the buffer of the central version being accessed and so it still does not see the user in the user catalog. This results in confusion for the user and the security administration function.

The ideal solution would have the read only service read the updated pages from disk. This is exactly the solution provided by EZ-Synchro. The combination of EZ-Synchro and central security means that changes can be made to the security definitions with such changes IMMEDIATELY reflected across the SECURITY DOMAIN.