1.2 Flashcards
What is meant by large database performance?
When many users and applications simultaneously access large databases, query response time degrades rapidly. Database systems must maintain fast response times by structuring data properly on storage media and processing queries efficiently.
What is meant by database authorization?
Many database users should have limited access to specific tables, columns, or rows of a database. Database systems must authorize individual users to access specific data.
What is database security?
Database systems must ensure authorized users only access permissible data. Database systems must also protect against hackers by encrypting data and restricting access.
What are database rules?
Database systems must ensure data is consistent with structural and business rules. Ex: When multiple copies of data are stored in different locations, copies must be synchronized as data is updated. Ex: When a course number appears in a student registration record, the course must exist in the course catalog.
Describe database recovery?
Computers, database systems, and individual transactions occasionally fail. Database systems must recover from failures and restore the database to a consistent state without loss of data.
What is a transaction?
A transaction is a group of queries that must be either completed or rejected as a whole. Execution of some, but not all, queries results in inconsistent or incorrect data.
What must database systems do when processing transactions?
- Ensure transactions are processed completely or not at all.
- Prevent conflicts between concurrent transactions.
-Ensure transaction results are never lost.
What is database architecture?
The architecture of a database system describes the internal components and the relationships between components.
What does the query processor do?
The query processor interprets queries, creates a plan to modify the database or retrieve data, and returns query results to the application.
Why does the query processor perform query optimization?
The query processor performs query optimization to ensure the most efficient instructions are executed on the data.
What does the storage manager do?
The storage manager translates the query processor instructions into low-level file-system commands that modify or retrieve data.
Why does the storage manager use indexes?
Since database sizes range from megabytes to many terabytes, the storage manager uses indexes to quickly locate data.
What does the transaction manager do?
The transaction manager ensures transactions are properly executed. The transaction manager prevents conflicts between concurrent transactions. The transaction manager also restores the database to a consistent state in the event of a transaction or system failure.
What is a log?
The log is a file containing a complete record of all inserts, updates, and deletes processed by the database. The transaction manager writes log records before applying changes to the database. In the event of a failure, the transaction manager uses log records to restore the database.
What is a catalog (aka data dictionary)?
The catalog, also known as a data dictionary, is a directory of tables, columns, indexes, and other database objects. Other components use catalog information to process and execute queries.
