File structures
Index File
- Data file is accompanied by index file
- Index file provides pointers to the beginning of sections of the data file beginning with a new letter
- advantages
- index is very small and can be read into RAM
- binary search done on index which is extremely fast
- disadvantages
- number of records at each letter may be unevenly distributed so in places searching could be slow
- index could be more detailed but this increases the space required
- updating is difficult and slow because both file and index must be revised