9 Top Features of IMS DB HDAM Database

Here are features of IMS HDAM database.

HDAM Database

  1. An HDAM database consists of one data set which is split into two parts: the root addressable part and the overflow part.
  2. The data set is a VSAM ESDS or OSAM data set. Click here HDAM Database Diagram
  3. 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.
  4. 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.
  5. Once a segment has been inserted in a HDAM database, the segment is never moved in order to preserve all the direct address pointers.
  6. 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.
  7. 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.
  8. Full Function data bases – can be accessed by SQL, DB2 and Oracle. They have both primary and Secondary index
  9. Fast Path databases, are mainly being used in extremely high transaction rate environment


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Experienced software developer. Skills in Development, Coding, Testing and Debugging. Good Data analytic skills (Data Warehousing and BI). Also skills in Mainframe.