Storage management:
A database system is portioned into modules that
deal with each of the responsibilities of the overall system. The functional
components of a database system can be broadly divided into the storage
manager and the query processor components.
A storage manager is a program module that provides
the interface between the low-level data stored in the database and the
application programs and queries submitted to the system.
Ø The
storage manager is responsible to the following tasks:
(i) Interaction with the file manager (OS)
(ii) Efficient storage, retrieval and updating of
data
Ø The
storage manager components include:
(i) Authorization and integrity manager:
Test integrity constraints and checks the authority of users to access data.
(ii) Transaction manager:
Ensures consistency of the DB despite system failures.
(iii) File manager:
Allocation of space + data structure used to represent information stored in
the disk.
(iv) Buffer manager:
Responsible for fetching data from disk storage into main memory and deciding
what data to cache in the main memory.
Ø The
storage manager implements several data structures as part of the physical
system implementation:
(i) Data files:
which store the database itself (relations).
(ii) Data dictionary:
Stores the metadata about the structure of the database (sometimes called
catalog).
(iii) Indices:
Provide fast access to data items. Like the index of a text book, a database;
index provides pointers to those data items that hold a particular value.
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