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Chapter 14: Problem 2

What are the differences among primary, secondary, and clustering indexes? How do these differences affect the ways in which these indexes are implemented? Which of the indexes are dense, and which are not?

Short Answer

Expert verified
Primary indexes are connected to the data with a unique index value per row, while secondary and clustering indexes are not. The primary index is sparse, secondary indexes are dense and can exist multiple times, while clustering indexes aid in data grouping and faster data retrieval.

Step by step solution

01

Understanding Indexes

An index in a database is similar to an index at the end of a book. It's a data structure, which improves the speed of operations in a database. There are three common types of indexes: primary, secondary, and clustering.
02

Primary Indexes

Primary Index is an ordered file which is sparse. The records are ordered by the primary key of the database. It's directly connected to the data, there's only one primary index per database. This type implies the maintenance of a unique index value for each row in the database table.
03

Secondary Indexes

The secondary index could be generated from a field which is a candidate key and has a unique value in each record, or non-key with duplicate values. Secondary indexes could be more than one for a single database.
04

Clustering Indexes

Clustering index is shared among all physical records of a database. With this type of index, records with similar characteristics are grouped together and indexes are created for these clusters of data.
05

Index Implementation

The differences between types of indexes primarily affect their implementation: Primary indexes are directly connected to the data and only one can exist per database, while secondary and clustering indexes are not directly connected to data. Secondary indexes can exist multiple times for a database and clustering indexes help with data clustering and improve data retrieval speed.
06

Dense and Sparse Indexes

Primary and clustering indexes are sparse as they do not have an index entry for every search key. Only the first record of each block has an index entry. On the other hand, secondary indexes are dense, as they have an index entry for every search key and pointer to the block in the data file.

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Most popular questions from this chapter

What is the order \(\mathrm{p}\) of a \(\mathrm{B}^{+}\) -tree? Describe the structure of both internal and leaf nodes of a \(\mathrm{B}^{+}\) -tree.

What is a fully inverted file? What is an indexed sequential file?

as key field includes records with the following Part# values: 23,65,37,60,46,92,48, 71,56,59,18,21,10,74,78,15,16,20,24,28,39, 43,47,50,69,75,8,… # A PARTS file with Part# as key field includes records with the following Part# values: 23,65,37,60,46,92,48, 71,56,59,18,21,10,74,78,15,16,20,24,28,39, 43,47,50,69,75,8,49,33,38. Suppose that the search field values are inserted in the given order in a W -tree of order p = 4 and Pleaf = 3; show how the tree will expand and what the final tree will look like.

Define the following terms: indexing field, primary key field, clustering field, secondary key freld, block anchor, dense index, and nondense (sparse) index.

What is the order \(p\) of a B-tree? Describe the structure of B-tree nodes.
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