Indexes

Primary Index

defined on an ordered data file the data file is ordered on a key field includes one index entry for each block in the data file a primary index is a nondense (sparse) index, since it includes an entry for each disk block of the data file

Clustering Index

defined on an ordered data file the data file is ordered on a non-key field includes one index for each distinct value of the field; the index entry points to the first data block that contains records with that field value it is another example of a nondense index

Multi-level indeces

most use a B+ tree data structure because of the insertion and deletion problem because a single-level index is an ordered file, we can create a primary index to the index itself a multi-level index can be created for any type of first-level index (primary, secondary, clustering) as long as the first-level index consists of more than one disk block

Secondary Index

provides a secondary means of accessing a file for which some primary access already exists may be on a field which is a candidate key and has a unique value in every record, or a non-key field with duplicate values the index is an ordered file with two fields includes one entry for each record in the data file; hence, it is a dense index

B+ Tree

variations of search trees that allow efficient insertion and deletion of new search values each node corresponds to a disk block each node is kept between half-full and completely full