Hello friends, Today we are going to learn about what is database access and how it works. So let’s go to the article.
Database Access
DBMS is the bridge between the user and the database. To access the database, the following steps are involved.
Step 1. The user sends a query to the data manager, which is the central software component of the DBMS, to retrieve the set of records.
Step 2. The data manager analyzes the external schema of the user program and finds the database description of the record.
Step 3. The data manager then checks with the conceptual schema to get the data types and location information.
Step 4. The data manager then checks with the physical schema to find out with device the record is in and what Data Manager can use access methods.
Step 5.6. It then sends a request to the file manager for locating a block containing a required record that requests this block from the disk manager, which performs the physical input and output operation to access the required records from the database.
Step 7. The retrieved data is placed into the system buffer (Reserved blocks of primary memory to match the speed of the processor and relatively fast primary memories with the slower secondary memories and minimize the I/O operations between secondary and primary memories).
Step 8. Now the retrieved are sent from the system buffer to the DBMS/User Interface with the help of DBMS.
Step 9. It provides the status information.
In the database access, the storage manager components are responsible for providing the interface between the low-level data stored in the database and the application programs and queries submitted to the system.
The following are the storage manager components :
- Data Manager
- File Manager
- Disk Manager
- Buffer Manager
Data Manager
The data manager is the leading software component of the DBMS. The main functions of the Data Manager are
- It transforms operation in the user queries or an application program from the user’s logical view to a physical file system.
- Data Manager handles the buffers in the main memory.
- It enforces constraints to the integrity and consistency of the data.
- Data Manager synchronizes the operation performed by the user simultaneously.
- It also controls backup and recovery operations.
File Manager
The file manager’s responsibility is to allocate the space on disk storage, and the data structures used to represent information stored on disks. After fetching the record, the file manager sends the requested record back to the data manager. The file manager is not concerned with the physical characteristics of the underlying storage media.
Disk Manager
The disk manager is the part of the operating system which accepts a requested block or page containing the required record from the file manager. It sends it to the database to perform input/output operations. Then after accessing it returns the requested block to the file manager is not concerned with the physical characteristics of the storage media.
Buffer Manager
Buffer Manager is responsible for fetching data from disk storage into main memory and deciding what data to cache in memory.
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