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Flexible Hashing

Hashing analysis above assumes fixed file size (b).

Not useful for DBMSs, where tables (files) are dynamic.

Several schemes have been proposed to hash such files.

Two methods access pages via a directory:

  • dynamic hashing
  • extendible hashing
The third method requires no directory (systematic file expansion):
  • linear hashing
All methods:
  • treat hash value as bit-string   (k bits, where 2k b)
  • adjust hash function by altering number of bits considered