- An HDAM database consists of one data set which is split into two parts: the root addressable part and the overflow part.
- The data set is a VSAM ESDS or OSAM data set. Click here HDAM Database Diagram
- After initial load, segments within a database record are very likely to be grouped together in blocks/CIs in hierarchical order. After update activity, this may not be the case.
- To insert a root segment, IMS first invokes the HDAM randomizer that has been specified in the DBD. This will determine the RAP from which this root must been chained.
- Once a segment has been inserted in a HDAM database, the segment is never moved in order to preserve all the direct address pointers.
- If segments are deleted from the database segment, they will be physically deleted from the data set, and the space will be designated as free space.
- If the database were to use multiple data set groups, each secondary data set group would have the format of the overflow part of an HDAM database.
- Full Function data bases – can be accessed by SQL, DB2 and Oracle. They have both primary and Secondary index
- Fast Path databases, are mainly being used in extremely high transaction rate environment