Indexing Structures in Databases

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Questions and Answers

What is the main purpose of using indexes in a database?

To organize data files into a specific order.

To provide faster retrieval of records based on specific search conditions. (correct)

To store and manage the data dictionary of a database.

To create backup copies of data files for recovery purposes.

Which of the following is NOT a characteristic of a dense index?

Provides faster retrieval for specific search conditions.

Utilizes fewer disk blocks compared to a sparse index. (correct)

Contains an entry for every record in the data file.

Offers a comprehensive index for all values of the search key.

Which type of index is defined on the ordering key field of a data file?

Sparse Index

Clustering Index

Primary Index (correct)

Secondary Index

How is a single-level ordered index similar to an index in a textbook?

It uses a consistent order for storing data entries. (D) Signup and view all the answers

What is the defining characteristic of a sparse index compared to a dense index?

It only has index entries for a subset of the search key values. (D) Signup and view all the answers

When using a single-level ordered index, how is a binary search beneficial?

It efficiently locates the specific block containing the desired record by dividing the search space in half repeatedly. (B) Signup and view all the answers

Which statement best describes the relationship between an index file and the corresponding data file?

The index file contains pointers to records in the data file. (B) Signup and view all the answers

Which statement best describes the role of indexing structures in physical database design?

They optimize physical storage and retrieval of data by providing efficient access paths. (D) Signup and view all the answers

What is the primary function of a clustering index?

To manage records with the same ordering field values (C) Signup and view all the answers

In the context of a primary index, what does the block anchor refer to?

The first record in a block which serves as a reference point (C) Signup and view all the answers

What characteristic defines a primary index?

It is a sparse index that corresponds to each disk block (D) Signup and view all the answers

If the blocking factor, Bfr, is calculated to be 3 for a data file, how many records will fit in each block?

3 records per block (D) Signup and view all the answers

What is the maximum number of secondary indexes that can be defined on a data file?

Unlimited secondary indexes on nonordering fields (B) Signup and view all the answers

What is the calculated size of an index entry (RI) if the VSSN is 9 and PR is 7?

16 bytes (D) Signup and view all the answers

How many entries can fit in one block if the block size is 512 bytes and the index entry size is 16 bytes?

32 entries (C) Signup and view all the answers

What is the number of index blocks (bI) needed if there are 10,000 records and each block can hold 32 entries?

313 blocks (D) Signup and view all the answers

What is the number of block accesses required for a binary search on 313 blocks?

9 block accesses (A) Signup and view all the answers

Which characteristic distinguishes a clustering index from a primary index?

Points to the first data block with the field value (C) Signup and view all the answers

What is a potential downside of secondary indexes compared to primary indexes?

Higher storage space requirements (C) Signup and view all the answers

What does a dense secondary index on a non-ordering candidate key field include?

Block pointers for each record (B) Signup and view all the answers

What is a clustering index primarily based on?

Non-key fields in an ordered file (A) Signup and view all the answers

What is the purpose of using variable-length records in index entries?

To allow for multiple pointers for each index field value. (A) Signup and view all the answers

What is a benefit of using a multilevel index?

It improves query performance by reducing search space. (B) Signup and view all the answers

In a nondense indexing scheme, what does the pointer in an index entry point to?

To a disk block containing a set of record pointers. (A) Signup and view all the answers

What is an essential characteristic of the first-level index in a multilevel index structure?

It must be ordered. (B) Signup and view all the answers

How does the size of an index record impact the number of disk block accesses needed to retrieve a record?

Smaller index records require fewer disk accesses. (A) Signup and view all the answers

What does the second level of a multilevel index serve as?

A primary index to the first level. (B) Signup and view all the answers

When using a multilevel index, how can you extend the indexing structure?

By repeating the process creating more levels. (A) Signup and view all the answers

What scenario is described by using an unspanned allocation?

Records are not allowed to span more than one disk block. (A) Signup and view all the answers

How many blocks would it take to store 1,000,000 records if each block can hold 4 records?

250,000 (B) Signup and view all the answers

What is the average access time in blocks for accessing a record using a primary index with a block size of 4096 bytes and a record size of 32 bytes?

12 (B) Signup and view all the answers

What is the primary advantage of using a multilevel index over a single-level index for searching records?

Multilevel indexes reduce the number of blocks accessed during a search. (C) Signup and view all the answers

What is the main problem associated with using a physically ordered index for data insertion and deletion?

It requires frequent reorganization of the index. (D) Signup and view all the answers

What is the primary purpose of using B-trees and B+ -trees in dynamic multilevel indexes?

To improve the efficiency of data insertion and deletion. (B) Signup and view all the answers

What is a key characteristic of B+-trees compared to B-trees?

Data pointers are stored only at the leaf nodes in B+-trees. (C) Signup and view all the answers

In a B+-tree of order p=4, how many pointers and key values does each node contain?

4 pointers and 3 key values. (B) Signup and view all the answers

What happens when a node in a B+-tree reaches its capacity upon insertion?

The node is split. (B) Signup and view all the answers

How does the structure of leaves in a B+-tree differ from that in a B-tree?

Leaf nodes in B+-trees have data pointers for every search field value. (B) Signup and view all the answers

Which of the following statements is true regarding internal nodes in B+-trees?

They contain search values to guide searches. (D) Signup and view all the answers

What is the significance of the 'mid element' during insertion in a B+-tree?

It identifies whether to split the node. (D) Signup and view all the answers

What is the maximum number of key values for a node in a B-tree of order p=4?

3 (B) Signup and view all the answers

Which of the following is NOT a characteristic of B+-trees?

All search field values are stored in internal nodes. (D) Signup and view all the answers

What ensures that a B+-tree maintains a balanced structure?

Node splitting upon reaching maximum capacity. (C) Signup and view all the answers

What are the consequences of repeated entries in internal nodes of a B+-tree?

Redundant data storage. (C) Signup and view all the answers

Study Notes

Indexing Structures for Files and Physical Database Design

Indexing is used to speed up record retrieval based on specific search criteria.
Indexing structures provide secondary access paths.
Any field can be used to create an index.
Indexes are usually defined on one field but can be on multiple fields.
A single-level index is an auxiliary file that enhances record retrieval efficiency in data files.
A single-level index structure usually contains entries with <field value, pointer to record>, ordered by field value.
Most indexing structures use tree data structures to organize the index.
Index file size is typically smaller than the data file size because index entries are smaller.
Binary searches on the index quickly locate pointers to the desired data records.
Indexes can be categorized into dense or sparse (non-dense).

Dense vs. Sparse Index

A dense index has an index entry for every search key value in the data file.
In a dense index, every data record has a corresponding entry in the index.
A sparse index, on the other hand, has index entries for only some of the search key values.
Sparse indexes skip some search key values and only include entries for specific values, often the starting record of a block in the data file.

Types of Single-Level Ordered Indexes

Primary Index: The index is built on the primary key field, which uniquely identifies each record in the data file. Primary indexes are used when records must be retrieved strictly in sorted order, and the field used as the primary key will uniquely identify each record in the data file.
Clustering Index: Used efficiently when many records have the same value for the ordering field. It creates an index based on the non-key field, with one index entry for each distinct value. The index entry points to the first data block containing the records having that non-key field value.
Secondary Index: Provides secondary access paths, independent of the primary key. Secondary indexes can use any non-ordering field in the data file and accommodate duplicate entries.

Primary Index

Ordered file with two fields: Primary key and pointer to a specific disk block.
It defines an index based on an ordered data file.
The data file is ordered on a key field.
Each entry in the index file maps a unique primary key value to the disk block address that contains the corresponding record.
One index entry exists for each block in the indexed data file. The index entry holds the key value for the first record within that block (the block anchor).
It is a nondense index—it doesn't include an entry for every possible search value, but merely the anchor record's key.

Clustering Indexes

Ordered file with two fields: Non-key field and pointer to a disk block.
It is built on a non-key field.
The data file is ordered on a non-key field, unlike a primary index, where records must have unique values.
One index entry exists for every unique non-key field value, and points to the first data block containing records with that value.
Insertion and deletion operations are straightforward in clustering indexes.

Secondary Indexes

Provides secondary means of accessing files for which primary access exists.
Secondary indexes are ordered files with two fields: a non-key field and a pointer.
The data file can be ordered or unordered.
Secondary indexes can be built on non-key fields with unique or duplicate values.
They typically use more storage space and take more time to search than primary indexes.
Multiple secondary indexes are possible for the same data file (on different fields).

Multilevel Indexes

Multilevel indexes are created by indexing the index itself, resulting in multiple levels of indexes. This optimizes the search time significantly when data is huge.
Each level of a multilevel index (except the base level) is a primary index of the preceding level.
The process is repeated until the top-level index fits within one disk block.
Multilevel indexes are generally employed when the size of the index in the initial level is large.
Dynamic multilevel indexes (like B-trees, and B+ -trees) are designed to efficiently handle insertions and deletions in the index without compromising the tree structure's balance.

Dynamic Multilevel Indexes (B-Trees and B+-Trees)

B-trees and B+-trees are dynamic multilevel indexes that self-adjust to insertions and deletions of records, maintaining a balanced structure.
In B-trees, pointers to data records can occur at any level.
In B+-trees, data pointers are exclusively located at the leaf node level.
B-Trees and B+-Trees provide balanced structures, allowing fast insertion and deletion of records, while preventing leaf nodes from exceeding maximum capacity.

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Description

This quiz covers the fundamental concepts of indexing structures used in physical database design. It includes topics such as single-level indexes, dense versus sparse indexing, and the role of tree data structures in organizing index entries. Test your knowledge on how indexing enhances record retrieval efficiency in databases.