Main storage databases (MSDBs)

The MSDB structure consists of fixed-length root segments only, although the root segment length can vary between MSDBs.

The maximum length of any segment is 32,000 bytes with a maximum key length of 240 bytes. Additional prefix data extends the maximum total record size to 32,258 bytes.

The following options are not available for MSDBs:

Multiple data set groups
Logical relationships
Secondary indexing
Variable-length segments
Field-level sensitivity

The MSDB family of databases consists of four types:

Terminal-related fixed database
Terminal-related dynamic database
Non-terminal-related database with terminal keys
Non-terminal-related database without terminal keys

Recommendation: Use DEDBs instead of MSDBs when you develop new Fast Path databases. Terminal-related MSDBs and non-terminal-related MSDBs with terminal-related keys are no longer supported. Although non-terminal-related MSDBs with non-terminal-related-keys are still supported, you should consider converting any existing MSDBs to DEDBs. You can use the MSDB-to-DEDB Conversion utility.

An MSDB is defined in the DBD in the same way as any other IMS database, by coding ACCESS=MSDB in the DBD statement. The REL keyword in the DATASET statement selects one of the four MSDB types.

Both dynamic and fixed terminal-related MSDBs have the following characteristics:

The record can be updated only through processing of messages issued from the LTERM that owns the record. However, the record can be read using messages from any LTERM.
The name of the LTERM that owns a segment is the key of the segment. An LTERM cannot own more than one segment in any one MSDB.
The key does not reside in the stored segment.
Each segment in a fixed terminal-related MSDB is assigned to and owned by a different LTERM.

Terminal-related MSDBs cannot be accessed by ETO terminals.

Non-terminal-related MSDBs have the following characteristics:

No ownership of segments exists.
No insert or delete calls are allowed.
The key of segments can be an LTERM name or a field in the segment. As with a terminal-related MSDB, if the key is an LTERM name, it does not reside in the segment. If the key is not an LTERM name, it resides in the sequence field of the segment. If the key resides in the segment, the segments must be loaded in key sequence because, when a qualified SSA is issued on the key field, a binary search is initiated.