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Chapter 25: Technical Specifications

The Remote IMS features are:

25.1 Restrictions

This section describes restrictions with Remote IMS.

25.1.1 IMS Option Definition Restrictions

Since IMS Option performs DL/I call validation and routes the call to the Requester, any database calls which cannot pass IMS Option SSA and PCB editing cannot be used with Remote IMS. This minimally requires that the DBD and PSB can be successfully genned with IMS Option.

25.1.2 PCB Field Level Sensitivity

PCB Field Level Sensitivity and the use of Processing Option "K" are only supported for retrieval calls and only when the Remote Server uses the AIBTDLI call interface. The reason for this is that the Remote Requester ignores these PCB related options when packaging the segment I/O areas for update calls and when creating the Segment Length Descriptors for the CBLTDLI Server calls. See the chapter Advanced Server Configuration for instructions on setting up processing for the AIBTDLI Server call. The Server can use AIBTDLI even when the application originally called a language-dependent DLI entry point such as CBLTLDI or ASMTDLI.

25.1.3 Fast Path MSDB

IMS/ESA only supports limited access to Fast Path MSDB databases by CPI-C driven transactions. However, the Requester sends all calls issued to MSDBs to the Server for processing and relies on IMS/ESA to issue an appropriate status code if the call is not supported. The MSDB FLD call is not supported by the Requester. The FLD call is not supported because MSDBs are supported by IMS/ESA CPI-C transactions for read-only and the FLD call is often used for updating. The maximum length of a "DL/I packet" is limited to 32,000 bytes. See the chapter Advanced Server Configuration for an explanation of this DL/I packet.

25.1.4 GSAM Databases

GSAM databases are not supported with Remote IMS. The primary reason for this is that IMS/ESA does not support accessing GSAM databases from CPI-C driven transactions. However, mainframe GSAM databases can be accessed using DataConnect. See the section GSAM Considerations in the chapter For the Database Administrator (DBA) for details on accessing GSAM databases.

25.1.5 Dynamic Database Attach (DDBA)

The IMS Option Dynamic Database Attach (DDBA) facility has the ability to generate "ACBs" and PCBs dynamically from a DBD name. A dynamically generated ACB cannot be used to access a remote database as there is no way to generate an ACB dynamically on IMS/ESA for database PCBs. With DDBA, you must use the "Schedule PSB" call which creates an "ACB" in IMS Option suitable for accessing remote databases. In addition, the Requester does not adjust the relative PCB numbers for the Remote IMS Server and thus requires the "IOPCB" option on the DDBA Schedule PSB call.

25.1.6 IMS/ESA Restrictions

The Remote IMS Server is essentially an online IMS/ESA application which can only access resources that are managed by IMS/ESA. PSBs and databases that will be accessed by Remote IMS must be available to the IMS/ESA DB/DC environment.

PSBs must be defined in Stage 1 input APPLCTN Macros and included in an ACBGEN. Databases must be defined in Stage 1 input DATABASE Macros and their DD statements available to the IMS control region. 'Off-line' database data sets, such as those accessed using DBBBATCH, are not available to Remote IMS.

25.1.7 Parallel Scheduling

Defining a PSB for 'parallel' scheduling allows the PSB to be scheduled in more than one region at the same time. In Remote IMS terms, this means it can be accessed by more than one user at the same time. This is because Remote IMS schedules a PSB instance for each user. When a PSB is not defined for parallel scheduling, it is 'serial' and is only available to one user at a time. The parallel/serial designation is specified in the IMS/ESA Stage 1 input APPLCTN Macro SCHDTYP parameter.

25.2 Other DL/I Technical Details

The Requester increases the relative PCB number by one when a DL/I type program is running under IMS Option with a PSB defined with CMPAT=NO. This is required so that the PCB number the Requester sends to the Server for calling CBLTDLI is the correct number for the PSB scheduled on IMS/ESA. The PCB list in the Server always contains an IO PCB as the first PCB. If the PCBNAME is defined for the PCB and you are using "Automatic AIB Calling", this adjustment is not necessary. See the section AIBTDLI Availability in the chapter Advanced Server Configuration for details about this feature.

Remote IMS uses the DBD and PSB Gen information that has been defined in your IMS Option system. You need to ensure that changes to the Gens are reflected in your IMS/ESA and IMS Option systems. Problems may occur if they are not the same. In general, if the PSB definitions are not the same, DL/I calls may fail but your data is not affected. However, structural changes to your DBDs that are not reflected in both systems may result in corruption of your databases. For example, if you increase the length of a segment on your IMS/ESA DBD but do not change it in IMS Option, the Requester does not send enough data from the application to the Server when inserting a segment to the Server. The "extra" data inserted to IMS/ESA is whatever is in the Server's buffer from the previous DL/I call.

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