Oracle DBA key terms

The shared memory region allocated when an Oracle instance starts. It holds the buffer cache, shared pool, redo log buffer, and other memory structures shared by all server and background processes attached to the instance.

A private memory area allocated for each server process. It stores session-specific information such as bind variables, sort areas, and cursor state, and can be sized automatically by the instance.

A background process that performs instance recovery at startup when needed, cleans up temporary segments, coalesces free space, and recovers transactions left over from a failed instance.

A background process that cleans up after abnormally terminated user processes by rolling back the transaction, releasing locks, and freeing resources; it also registers instance services with the listener.

The background process that writes modified, or dirty, buffers from the database buffer cache to data files, keeping cache space available and advancing the instance checkpoint.

The background process that writes redo entries from the redo log buffer to the online redo log files, typically on commit, making committed changes recoverable.

The mechanism, driven by the checkpoint process, that records a consistent point in time: dirty buffers are written out and file headers plus the control file are updated with the checkpoint position.

A small binary file that records the physical structure of the database, including data files, redo log members, log sequence numbers, and checkpoint details. The instance cannot mount without it.

A set of files that record every change made to the database. Redo entries are written before data blocks, so changes can be replayed during instance or media recovery.

A saved copy of a filled online redo log file, produced by an archiver process. Archived logs allow recovery of changes made after a backup was taken.

A binary, server-side initialization file that the instance reads at startup and can modify through ALTER SYSTEM, so parameter changes persist across restarts.

The startup sequence of NOMOUNT, MOUNT, and OPEN. NOMOUNT builds the instance and reads parameters; MOUNT opens the control file; OPEN makes data files available for user transactions.

A server-side process that waits for incoming connection requests, passes each client to a server process, and can start instances dynamically through service registration.

A client-side Oracle Net configuration file that maps net service names to connect descriptors, letting users connect with a short alias instead of full host, port, and service details.

A logical storage container that groups one or more data files. Tables, indexes, and other objects are placed in tablespaces rather than being tied directly to individual operating-system files.

An operating-system file that belongs to exactly one tablespace and holds the data blocks of the database objects stored in that tablespace.

The set of extents allocated to a single database object such as a table, index, or undo segment. It is the storage representation of that object inside a tablespace.

A feature in which the database automatically creates, names, and deletes operating-system files based on a few directory parameters, so administrators do not name or track files manually.

A volume manager and file system built into Oracle that stripes and mirrors database files across disks and manages disk group membership independently of the operating system.

The collection of database objects owned by a single user account. Creating a user implicitly creates a schema with the same name as that user.

A named set of password and resource limits assigned to users. Policies such as password lifetime, reuse, and failed login attempts are enforced through the user's profile.

A right to perform a database-wide action, such as CREATE SESSION or CREATE TABLE, granted to a user or role rather than to a specific named object.

A named group of privileges that can be granted to users or to other roles, simplifying administration because many privileges are managed and revoked as a single unit.

An external file holding usernames and password hashes for administrative accounts. It authenticates privileged connections such as SYSDBA when the database is not open.

A logical unit of work in which all changes either commit together as a consistent whole or are rolled back entirely. It begins with the first change after a commit or rollback.

A lock taken automatically on rows changed by INSERT, UPDATE, or DELETE. It blocks other sessions from changing the same rows until the transaction ends, while readers are not blocked.

A situation in which two or more sessions each wait for a lock held by another, forming a cycle. Oracle detects the cycle and rolls back one statement with error ORA-00060.

A locally managed tablespace holding the undo segments Oracle uses to roll back uncommitted changes, provide read consistency, and support flashback features.

The minimum period for which Oracle tries to keep committed undo data available, so long-running queries and flashback queries can still see older versions of changed blocks.

An error raised when a query needs an earlier version of a block but the undo information required to reconstruct it has already been overwritten, usually because undo retention was too short.

The auditing framework in which policy-based audit records from all components are written to a single unified audit trail inside the database instead of separate traditional trails.

A policy-based auditing feature that records access to specific columns or rows, capturing the SQL text and the conditions under which the data was queried or changed.

Oracle's built-in backup and recovery client. It connects to a target database and backs up, validates, restores, and recovers data files, archived logs, and control files.

An optional schema in a separate database that stores RMAN metadata such as backup history and stored scripts, so backups remain manageable beyond the target control file's retention.

Restoring data files and then applying redo up to a chosen moment, so the database reflects a state before an unwanted change such as a dropped table or bad batch load.

A database mode in which filled online redo log files are archived before being reused. It is required for media recovery and for consistent backups taken while the database is open.

A server-side utility, run as expdp and impdp, that moves data and metadata between databases quickly, supporting parallel workers, filtering, and direct network-mode imports.

A utility that loads data from external text or binary files into Oracle tables, using a control file that describes the layout and format of the input records.

A table whose data resides in an operating-system file outside the database. Querying it reads the file through an access driver rather than through database data blocks.

A database object that maps a name to an operating-system directory path on the server, giving Data Pump, external tables, and BFILE columns controlled access to server files.