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“Oracle数据库的物理文件是存储在磁盘上的数据文件、控制文件和日志文件的总称。数据文件和日志文件是数据库中最重要的文件。数据库由若干个表空间组成，表空间由表组成，表由段组成，段由区间组成，区间由数据块组成。那么，数据在数据文件中是如何组织的呢？要了解这些内容我们首先必须理解什么是表空间（tablespace）、段（segment）、区（extent）、块（block），这些都是oracle数据库在数据文件中组织数据的基本单元。”
| 概念 | 中文 | 描述 |
| query transformer | 查询转换组件 | An optimizer component that decides whether it can rewrite the original SQL statement into a semantically equivalent SQL statement with a lower cost. |
| R | R语言 | A language and environment for statistical computing and graphics. |
| range partitioning | 范围分区 | A type of partitioning in which the database maps rows to partitions based on ranges of values of the partitioning key. Range partitioning is the most common type of partitioning and is often used with dates. |
| read committed isolation level | 读已提交隔离级别 | An isolation level that guarantees that a query executed by a transaction sees only data committed before the query—not the transaction—began. |
| read consistency | 读一致性 | A consistent view of data seen by a user. For example, in statement-level read consistency the set of data seen by a SQL statement remains constant throughout statement execution. See also data concurrency; data consistency. |
| read-only database | 只读数据库 | A database that is available for queries only and cannot be modified. |
| read-only isolation level | 只读隔离级别 | An isolation level that is similar to the serializable isolation level, with one exception: read-only transactions do not permit data to be modified in the transaction unless the user is SYS. |
| real-time redo transport | 实时重做传输 | The continuous transfer of redo changes from the SGA of a protected database to a Recovery Appliance. Real-time redo transport enables RMAN to provide a recovery point objective near 0. Typically, RMAN can recover to within a second of the time when the failure occurred. Protected databases write redo entries directly from the SGA to the Recovery Appliance as they are generated. |
| recoverable error | 可恢复错误 | A class of errors that arise because of an external system failure, independently of the application session logic that is executing. Recoverable errors occur following planned and unplanned outages of networks, nodes, storage, and databases. An example of a nonrecoverable error is submission of invalid data values. |
| recoverer process (RECO) | RECO（恢复进程） | In a distributed database, the background process that automatically resolves failures in distributed transactions. |
| Recovery Appliance | 恢复机 | Shortened name for Zero Data Loss Recovery Appliance. Recovery Appliance is an Oracle Engineered System specifically designed to protect Oracle databases. Integrated with RMAN, it enables a centralized, incremental-forever backup strategy for hundreds to thousands of databases across the enterprise, using cloud-scale, fully fault-tolerant hardware and storage. |
| Recovery Appliance Backup Module | 恢复机备份模块 | An Oracle-supplied SBT library that RMAN uses to send backups of protected databases over the network to the Recovery Appliance. The library must be installed in each Oracle home used by a protected database. The module functions as an SBT media management library that RMAN references when allocating or configuring a channel for backup to the Recovery Appliance. RMAN performs all backups to the Recovery Appliance, and all restores of complete backup sets, using this module. |
| Recovery Appliance metadata database | 恢复机元数据数据库 | The Oracle database that runs inside of the Recovery Appliance. This database stores configuration data such as user definitions, protection policy definitions, and client database definitions. The metadata database also stores backup metadata, including the contents of the delta store. |
| Recovery Appliance storage location | 恢复机存储位置 | A set of Oracle ASM disk groups within Recovery Appliance that stores backups. A storage location can be shared among multiple protected databases. Every Recovery Appliance contains the default Recovery Appliance storage location named DELTA. |
| recovery catalog | 恢复目录 | A centralized backup repository located in an Oracle database. The recovery catalog contains metadata about RMAN backups. |
| recovery window goal | 恢复窗口目标 | The time interval within which a protected database must be recoverable to satisfy business requirements. For each protected database in a protection policy, the Recovery Appliance attempts to ensure that the oldest backup on disk is able to support a point-in-time recovery to any time within the specified interval (for example, the past 7 days), counting backward from the current time. |
| recursive SQL | 递归SQL | SQL that the database executes in the background to obtain space for database objects. You can think of recursive SQL as "side effect" SQL. |
| redo log | 重做日志 | A set of files that protect altered database data in memory that has not been written to the data files. The redo log can consist of two parts: the online redo log and the archived redo log. |
| redo log buffer | 重做日志缓存 | Memory structure in the SGA that stores redo entries—a log of changes made to the database. The database writes the redo entries stored in the redo log buffers to an online redo log file, which the database uses when instance recovery is necessary. |
| redo record | 重做记录 | A record in the online redo log that holds a group of change vectors, each of which describes a change made to a data block. Each redo log file consists of redo records. |
| redo thread | 重做线程 | The redo generated by a database instance. |
| referenced key | 引用键 | In a foreign key relationship, the primary or unique key to which the foreign key refers. For example, in the common schema, the employees.department_id column is a foreign key, and the departments.department_id column is the referenced key. |
| referenced object | 引用对象 | In a schema object dependency, the object that is referenced by another object's definition. For example, if the definition of object A references object B, then B is a referenced object for A. |
| referential integrity | 引用完整性 | A rule defined on a key in one table that guarantees that the values in that key match the values in a key in a related table (the referenced value). |
| relation | 关系 | A set of tuples. |
| relational database | 关系数据库 | A database that conforms to the relational model, storing data in a set of simple relations. |
| RDBMS (relational database management system) | 关系型数据库管理系统 | A management system that moves data into a relational database, stores the data, and retrieves it so that applications can manipulate it. |
| replay context | 重播上下文 | In Application Continuity, opaque information that the database returns to the client driver during normal application run time. |
| replication | 复制 | The process of sharing database objects and data at multiple databases. |
| reserved pool | 保留池 | A memory area in the shared pool that Oracle Database can use to allocate large contiguous chunks of memory. |
| result set | 结果集 | The set of data retrieved from execution of a SELECT statement. |
| reverse key index | 反向键索引 | A type of B-tree index that physically reverses the bytes of each index key while keeping the column order. For example, if the index key is 20, and if the two bytes stored for this key in hexadecimal are C1,15 in a standard B-tree index, then a reverse key index stores the bytes as 15,C1. |
| right outer join | 右外连接 | The result of a right outer join for table A and B contains all records of the right table B, even if the join condition does not match a record in the left table A. For example, if you perform a right outer join of employees (left) to departments (right), and if some departments contain no employees, then the query returns rows from departments with no matches in employees. |
| RMAN (Recovery Manager) | RMAN (Recovery Manager) | An Oracle Database utility that backs up, restores, and recovers Oracle databases. |
| role | 角色 | A set of privileges that can be granted to database users or to other roles. |
| CDB root | CDB根 | In a multitenant container database (CDB), a collection of schemas, schema objects, and nonschema objects to which all PDBs belong. Every CDB has exactly one root container, which stores the system metadata required to manage PDBs. All PDBs belong to the CDB root. |
| row | 行 | A set of column information corresponding to a single record in a table. The database stores rows in data blocks. |
| row chaining | 行链 | A situation in which Oracle Database must store a row in a series or chain of blocks because it is too large to fit into a single block. |
| row lock | 行级锁 | A lock on a single row of table. A transaction acquires a row lock for each row modified by an INSERT, UPDATE, DELETE, MERGE, or SELECT ... FOR UPDATE statement. |