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Multi-level indexes

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Slideshow:

Prelude to multi-level indexes

Example: multi-level index

Example on using a multi-level index
                     
Find the record using search key D
Example on using a multi-level index

Find the entry ≤ D in the first index (use ≤ D because it's a (sparse) primary index)
Example on using a multi-level index

Follow the database address to next level of index file
Example on using a multi-level index

Search for the key = D in the data block (because it's a (dense) secondary index)
A very pouplar (dynamic) multi-level index

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• Multi-level index
  • Fact:

    An index file is also a data file            (It contains data !!!)

    Therefore:

    We can create an (primary) index on an index file !!!! Result: Multi-level index....

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  • Example: a multi-level index

    Notice that:

    The lowest level index (in the example: the secondary index) contains all the search keys !!!

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  • How to find the search key = D using the multi-leveled index:

    Procedure:

    Find the largest search key in the top level index such that key ≤ D : Follow the database address (link) to the next level: (We can repeat the step 1 and 2 if there are more index levels) In the lowest level of the index    (Note: the lowest level stores all search keys): Find the key D (We must search for the exact match - if not found, then the key is not stored in the data file) Graphically: Then follow the link to the data record(s)

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  • Note:

    We will soon discuss a dynamic multi-level index data structure: B-tree / B+-tree