Efficiency Unleashed: The Power of File Organization in Database Systems

The primary goal of the database is to store data and quickly access data.

It depends on these how is the data organized? Why do we have a database management system and not just many files? How does file organization improve efficiency?

Database systems do use files for storing data, but they utilize specialized file organization techniques to improve storage efficiency, access efficiency, and update efficiency. The main reasons to use specialized file organization over flat files are:-

1. Storage Efficiency: In a specialized file organization, the files are structured in a way that minimizes the storage overhead per stored record.

2. Access Efficiency: Specialized file organization aims to locate records in the minimum number of steps possible, thereby improving access efficiency. Instead of solely relying on filesystem hierarchy, databases use data structures like B-trees, indexes, or other indexing mechanisms.

3. Update Efficiency: Database systems optimize record updates to the minimum number of changes on disk. When an update occurs, only the affected data and index needs to be modified, rather than rewriting the entire file.

In a typical database system, data files and index files serve different purposes and store different types of information.

Data files are used to store actual data records in the database. These records contain the information that is being stored and managed by the database system.

Index files are used to store the metadata about the data records stored in the data files.

Data Files

Data files are implemented as a:

1. Index Organized Files

2. Heap Organized Files

3. Hash Organized Files

Heap Organized Files

Records in heap-organized files are not required to follow any particular order, and most of the time they are placed in a write order. This way, no additional work or file reorganization is required when new pages are appended.

Hash Organized Files

In hashed files, records are indeed stored in buckets, and the hash value of the key is used to determine which bucket a record belongs to. The hashing function takes the key as input and produces a hash value, which is used to calculate the address of the bucket in which the record should be stored.

Index Organized Files

Index-organized tables (IOTs) are a type of database storage structure where the data records are stored within the index itself, rather than in a separate data file. The primary key of the table serves as the index key, and the remaining attributes of the table are stored along with the key within the index structure.

Index Files

An index is a data structure that is used to organize data records on a disk in a way that enables efficient retrieval operations. It maps keys to the locations in data files where the corresponding records are stored. The primary purpose of an index is to speed up data retrieval by providing a quick lookup mechanism based on key values.

The primary index is specifically associated with the primary data file. It is usually built over the primary key or a set of keys identified as primary. The primary key uniquely identifies each record in the data file, and the primary index provides a direct mapping from the key value to the record's location on disk.

In contrast, secondary indexes are created on non-primary key fields or attributes. They can point directly to the data record or store the primary key of the record. If a secondary index points directly to the data record, it typically holds an offset to the data file (such as a heap file or an index-organized table) where the record is stored. Alternatively, the secondary index can simply store the primary key value of the record, allowing the index to indirectly locate the record.

It's important to note that multiple secondary indexes can exist in a database, and they can all point to the same data record. This means that a single data record can be identified and located through different indexes, providing flexibility in data retrieval based on different search criteria. Secondary indexes can be created on different fields or combinations of fields, allowing efficient retrieval based on various attributes.

While primary index files maintain a unique entry per search key, secondary indexes may have multiple entries for the same search key. This occurs when multiple records have the same value for the indexed attribute(s). Each entry in the secondary index corresponds to a record with a matching value, enabling efficient retrieval of records that satisfy specific search criteria.

By utilizing primary and secondary indexes, a database system can significantly improve the speed and efficiency of data retrieval operations by reducing the need for full table scans and enabling direct access to relevant records.