Managing the RDBMS

A single logical operation on the data is called a transaction.

ACID:

• Atomicity requires that database modifications must follow an “all or nothing” rule.
• Consistency enforces that the database remains in a consistent state Example: referential integrity implemented by Propagation constraints.
• Isolation ensures that other operations cannot access data that has been modified during a transaction that has not yet completed. A dirty read means that a transaction is allowed to read, but cannot modify, the uncommitted data from another transaction.
• Durability is ability of the DBMS to recover the committed transaction updates against any kind of system failure. Usually, transaction logs are used for this.

Backing up a Database:

1. Physical backup
   1. Cold backup after shutting down the database. Shutting down period may be long.
   2. Hot backup while database is online. May not allow transaction log to play against a backup taken this way.
2. Logical backup

• • Can`t do point-in-time recovery.
  • Referential Integrity may be lost   as loading needs information from another table.
  • Database have to be offline.

Data dictionary is a set of tables that provides information about the database details, basically meta-data information.

Backup creates a second copy. Data recovery restores a copy of data from back up.

Transaction log (also database log or binary log) is a history of actions executed by a database management system to guarantee ACID properties over crashes or hardware failures.