A modern database management system has a technique for the data structure that helps you retrieve data records from any system file. This technique is known as indexing. The index generally is a table with two columns. You will find a copy of the candidate or primary key in its first column. In contrast, its second column has a group of pointers containing the address for the disk block that keeps the storage address of the key’s particular value.
The index will-
- Take the search key as an input
- Effectively return a set of records that match this input
An insight into the different types of index in the database management systems
The following are the different types of indexing you can find in the database management systems-
The index is defined as per its attributes for indexing. There are two primary types of methods for indexing, and they are-
- Primary and
An overview of the primary index
The primary index is organized, has two fields, and a fixed file size. The first field has a primary key, and the second file points to the particular data block. There exists a one-on-one relationship between these two entities in the table. The primary index, again, can be divided into two kinds. They are-
- The dense index and
- The sparse index
The dense index refers to the record created in the database for each search key that is valued in it. It helps the user to search the database faster. However, it requires greater space for storing the records of the index. In this method, the records keep the search key’s value that points to the real record on its disk.
The sparse index refers to the index’s record that surfaces for just some values in this file. The sparse index assists you to resolve the problems of dense indexing present in the database management system. In the above indexing technique, the group of columns for the index contains a similar address for the data block, so when the data has to be retrieved, the address for this block data can be easily fetched.
However, one should note that the sparse index contains records for just some search key values. It requires less space and lesser maintenance overheads for insertions and deletions; however, compared to the above index for the location of records, it is much slower.
An overview of the secondary index
When it comes to the secondary index in the database management system, the field can be created with a specific record for every record. This should entail the candidate key and is often referred to as the non-clustering index too.
The technique is two-leveled in nature and can be deployed for reducing the size of the first level mapping at this level. Experienced DBAs say that a large volume of numbers is chosen, making the mapping small all the time.
The above can be better understood with the help of an easy illustration. In the case of a bank’s database, you will find the data is sequentially stored as per the account number, and you will find all the bank accounts of a particular branch of one bank, say XYZ Bank.
You can maintain a secondary index in the database management system for each search key. This index record is the point of record with all the groups of pointers to them in the particular value of the search key.
The clustering index is not a pointer, and the records are stored in the index independently. There are cases where this index is made on non-primary key columns. They do not need to be unique for every record. Professionals from the esteemed company in remote database management and administration, RemoteDBA.com, say that the user can make two or even more columns for getting unique values in such a case. In this way, an index can be made and named a clustered index so that the user can recognize the record quicker.
For instance, let us assume an organization has recruited several employees in different departments. In such a case, the clustering index in the database management system must be made for employees in the same department. This is considered one cluster, and the index points refer to the cluster as a whole. In this case, the department_ no is the non-unique key.
Understanding the multi-level index
Skilled professionals in database administration and management state a multi-level index is made when the primary index does not sync in with the memory. In this method, the user can reduce the volume of disk accesses to shorten any record stored on the disk as a sequential file to make a sparse base on the file.
This is a popular type of data structure in the database management system widely used for tree-based indexing. This format is multi-level and has binary search trees that are aligned. The leaf nodes in this index denote the real data pointers. These leaf nodes are also interlinked to the list of links that permit the B tree to offer both sequential and random access.
Skilled and experienced DBAs state that the B-Tree index should have the following traits-
- The lead nodes should have at least two to four values
- The path from the root to the leaf is generally equal in length
- These non-leaf nodes, besides the root node, generally have around three to five children nodes.
- Each node is neither a leaf nor a root node has n/2] and n children between them.
Professional experts in database performance tuning, management, and administration state indexing in database systems help you decrease the complete number of input and output operations required for retrieving that data so that you do not need to access the row in the database system from the index structure. In this way, you can get faster searches, and the retrieval of data becomes simpler for users.