Indexing in DBMS is a data structure technique that allows for efficient retrieval of records from a database file based on some attributes on which the indexing has been done. Indexing is used to optimize the performance of a database by minimizing the number of disk accesses required when a query is processed.

Some key points about indexing in DBMS include:

• Types of Indexing: There are several types of indexing in DBMS, including primary indexing, secondary indexing, and clustering indexing.

• Index Structure: An index is a small table that has two columns. The first column comprises a copy of the primary or candidate key of a table, while the second column contains a set of pointers for holding the address of the disk block where that specific key value is stored.

• Indexing Methods: There are several indexing methods, including ordered indices, dense indices, and sparse indices.

• Advantages and Disadvantages: Indexing can improve database performance by minimizing the number of disk accesses required to fulfill a query, but choosing the right indexes for a specific query or application can be challenging.

In summary, indexing in DBMS is a technique for improving database performance by reducing the number of disk accesses necessary when a query is run. It involves creating a data structure that allows for efficient retrieval of records from a database file based on some attributes on which the indexing has been done.