Organization of Records into Blocks:
- Block:
- A block is a contiguous sequence of data stored on a storage medium such as a disk.
- It is the smallest unit of data transfer between the disk and main memory.
- Typically, a block has a fixed size, often a multiple of the disk sector size.
- Block-Based Storage:
- Data is organized into blocks on storage media, and each block contains a fixed number of records.
- Records are read or written to/from blocks in their entirety, enhancing data transfer efficiency.
Sequential Files:
- Sequential File:
- In a sequential file organization, records are stored sequentially in the order they are inserted.
- Records can only be accessed sequentially from the beginning to the end of the file.
- Well-suited for applications with primarily sequential access patterns, such as transaction processing systems.
- Sequential File Structure:
- Consists of a series of blocks, with each block containing multiple records.
- Records are appended to the end of the file, and deleted records may leave gaps.
- Suitable for applications where data is primarily accessed in the order it was inserted.
Indexing:
- Index:
- An index is a data structure that provides fast access to records in a file based on a key value.
- It maps key values to the physical locations of corresponding records in the file.
- Types of Indexes:
- Primary Index: Index based on the primary key of the records. Typically implemented as a B-tree or a hash table.
- Secondary Index: Index based on non-primary keys to provide additional access paths to the data.
- Clustered Index: Index where the physical order of records in the file matches the order of the index. Often used in databases to optimize range queries.
- Non-clustered Index: Index where the physical order of records in the file does not match the order of the index. Requires additional lookups to retrieve records.
Hashing:
- Hash Function:
- A hash function is a function that maps keys to indexes in a hash table.
- It efficiently distributes keys across the hash table, minimizing collisions.
- Hashing:
- Hashing is a technique used to implement fast access to records based on a key value.
- Records are stored in a hash table, and a hash function is used to compute the index of each record in the table based on its key.
- Provides constant-time access to records on average, making it suitable for applications requiring fast access to individual records.
- Collision Resolution:
- Collisions occur when multiple keys map to the same index in the hash table.
- Techniques such as chaining (using linked lists) or open addressing (probing) are used to resolve collisions.
- Records are organized into blocks to optimize data transfer between storage media and main memory.
- Sequential files store records sequentially and are suitable for applications with primarily sequential access patterns.
- Indexing provides fast access to records based on key values, using data structures such as B-trees and hash tables.
- Hashing is a technique for implementing fast access to records based on key values, with collision resolution techniques to handle hash collisions.
By leveraging these techniques, applications can efficiently store and access records based on key values, optimizing performance and resource utilization.