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Internals of the Oracle segment header

Segment_header_block

Oracle Data Block consisting of 1) data block header, 2) table directory, 3) row directory 4) free space 5) row data
Oracle Data Block consisting of 1) data block header, 2) table directory, 3) row directory 4) free space 5) row data


  1. data block header: references information about the data block header
  2. table directory: references information about the tables which have rows in this block
  3. row directory: references information about actual rows, including an address for each row.
  4. free space: references information about the free space allocated for INSERT and UPDATE; actual use of free space depends on the value of
  5. PCTFREE row data: references information about table data and index data