What HDAM Provides
The HDAM access method provides hashed access to root segments and pointer access to child segments. The hashing algorithm calculates the physical address of a root segment occurrence based on the value in its sequence field.
HDAM Uses a Radomizing Routine
When a database record is first loaded, the HDAM method randomizes the root key value to a physical location, which consists of a block number and an offset into the block. The root segment occurrence and all dependent segment occurrences that will fit are loaded into the block. Dependent segment occurrences that will not fit are loaded into an overflow area. Physical child and physical twin pointers are created to establish the appropriate connections.
Fast and Direct Access to Root Segments
HDAM provides fast, direct access to a root segment occurrence. With, at most, one additional I/O, it is possible to access the first occurrence of the dependent segment at the next level by following the appropriate physical child pointer.
The HDAM method supports all of the DL/I hierarchical and logical relationships.
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