Work with access methods for DDM

Access methods control what subsets of functions can be performed after a particular remote file is opened. This might mean that an iSeries™ program, or a group of programs sharing a non-iSeries file, cannot do all the same operations that are possible using a file that is on the local iSeries server.

For example, assume that an iSeries application program opens a keyed file with SHARE(*YES) and performs keyed I/O operations. It then calls another program that does relative record number operations using the same open data path (ODP) (because SHARE was specified). Relative record numbers specify the relationship between the location of a record and the beginning of a database file, member, or subfile. If the first program is redirected by an Override with Database File (OVRDBF) command to use a remote keyed file on a System/36™, this scheme no longer works. If a keyed access method is selected, record number operations fail. If a record number access method is selected, keyed operations fail.

Notice that when both source and target servers are iSeries servers, access methods are not used. A potential problem exists when the target server is neither an iSeries server nor a System/38™. Notice also that the combined-access access method (*COMBINED) is not supported by System/36, and probably not by any target other than an iSeries server or System/38.

• Access intents
  When a program opens a file, it must specify how it intends to work with the records in the file: read, add, update, delete, or a combination of these.
• Key field updates
  An iSeries program is allowed to change any part of a data record including key fields.
• Deleted records
  On the iSeries server, a record is marked as deleted by the server.
• Blocked record processing
  If SEQONLY is used to block records sent to a remote server, the records are not sent until the block is full. If a source job is canceled before a block is sent, the records in the block are lost. If blocking is used, the user should make sure a force end of data or close of the file is done before canceling the source job.
• Variable-length records
  If your iSeries source server is running OS/400^® Version 2 Release 1 Modification 1, DDM supports variable-length record files as defined in the DDM architecture.