Database System Concepts (4) -- Indexing and Hashing

 Indexing and Hashing
    basic concepts
       two basic kind of indices: ordered indices and hash indices
       evaluating factors:
          Access types
          Access time
          Insertion time
          Deletion time
          Space overhead
       ordered indices
          primary index: an index whose search key also defines the sequential order of the file
              densw and sparse indices
              multilevel index: smaller!
          secondary indices: an index whose search key specifies an order different from the sequential order of the file
              must be dense, The pointer in a secondary index do not point directly to the file. Instead, each point to a bucket that contains pointers to the file.
   
       B+ Tree index files