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感觉Hash在数据库中是个非常重要的概念，有必要深入学习！
| 概念 | 中文 | 描述 |
| GDS catalog | GDS目录 | A metadata repository, located inside an Oracle database, that is associated with a GDS configuration. Every cloud has one and only one catalog. |
| GDS configuration | GDS配置 | A set of databases integrated by the GDS framework into a single virtual server that offers one or more global services while ensuring high performance, availability, and optimal utilization of resources. See also global service. |
| GDS pool | GDS池 | A set of databases within a GDS configuration that provides a unique set of global services and belongs to a specific administrative domain. |
| GDS region | GDS区域 | A logical boundary within a GDS configuration that contains database clients and servers that are geographically close to each other. |
| GDS (Global Data Services) | 全局数据服务 | An automated workload management solution for replicated databases. Database services are named representations of one or more database instances. GDS implements the Oracle Database service model across a set of replicated databases. |
| global partitioned index | 全局分区索引 | A B-tree index that is partitioned independently of the partitioning scheme used on the indexed table. A single index partition can point to any or all table partitions. |
| global service | 全局服务 | A database service provided by multiple databases synchronized through data replication. |
| global service manager | 全局服务管理程序(GSM) | The central management tool in the Global Data Services framework. At least one global service manager must exist in every GDS region of a GDS configuration. |
| granule | 颗粒（并行工作基本单元） | The basic unit of work in parallelism. Oracle Database divides the operation executed in parallel (for example, a table scan, table update, or index creation) into granules. Parallel execution processes execute the operation one granule at a time. |
| grid computing | 网格计算 | A computing architecture that coordinates large numbers of servers and storage to act as a single large computer. |
| grid infrastructure | 网格架构 | The software that provides the infrastructure for an enterprise grid architecture. In a cluster, this software includes Oracle Clusterware and Oracle ASM. For a standalone server, this software includes Oracle ASM. Oracle Database combines these products into one software installation called the Grid home. |
| hard parse | 硬解析 | The steps performed by the database to build a new executable version of application code. The database must perform a hard parse instead of a soft parse if the parsed representation of a submitted statement does not exist in the shared pool. |
| hash cluster | 哈希簇 | A type of table cluster that is similar to an indexed cluster, except the index key is replaced with a hash function. No separate cluster index exists. In a hash cluster, the data is the index. |
| hash collision | 哈希冲突 | Hashing multiple input values to the same output value. |
| hash function | 哈希函数 | A function that operates on an arbitrary-length input value and returns a fixed-length hash value. |
| hash join | 哈希连接 | A join in which the database uses the smaller of two tables or data sources to build a hash table in memory. The database scans the larger table, probing the hash table for the addresses of the matching rows in the smaller table. |
| hash key value | 哈希键值 | In a hash cluster, an actual or possible value inserted into the cluster key column. For example, if the cluster key is department_id, then hash key values could be 10, 20, 30, and so on. |
| hash partitioning | 哈希分区 | A partitioning strategy that maps rows to partitions based on a hashing algorithm that the database applies to the user-specified partitioning key. The destination of a row is determined by the internal hash function applied to the row by the database. The hashing algorithm is designed to distribute rows evenly across devices so that each partition contains about the same number of rows. |
| hash table | 哈希表 | An in-memory data structure that associates join keys with rows in a hash join. For example, in a join of the employees and departments tables, the join key might be the department ID. A hash function uses the join key to generate a hash value. This hash value is an index in an array, which is the hash table. |
| hash value | 哈希值 | In a hash cluster, a unique numeric ID that identifies a bucket. Oracle Database uses a hash function that accepts an infinite number of hash key values as input and sorts them into a finite number of buckets. Each hash value maps to the database block address for the block that stores the rows corresponding to the hash key value (department 10, 20, 30, and so on). |
| hashing | 哈希技术 | A mathematical technique in which an infinite set of input values is mapped to a finite set of output values, called hash values. Hashing is useful for rapid lookups of data in a hash table. |
| heap-organized table | 堆表 | A table in which the data rows are stored in no particular order on disk. By default, CREATE TABLE creates a heap-organized table. |
| hierarchical database | 层级数据库 | A database that organizes data in a tree structure. Each parent record has one or more child records, similar to the structure of a file system. |
| HWM (high water mark) | 高水位线 | The boundary between used and unused space in a segment. |
| hint | 提示指令 | An instruction passed to the optimizer through comments in a SQL statement. The optimizer uses hints to choose an execution plan for the statement. |
| hot buffer | 热缓存 | A buffer in the database buffer cache that is frequently accessed and has been recently used. |
| human error outage | 人为错误导致的中断 | An outage that occurs when unintentional or malicious actions are committed that cause data in the database to become logically corrupt or unusable. |
| image copy | 镜像副本 | A bit-for-bit, on-disk duplicate of a data file, control file, or archived redo log file. You can create image copies of physical files with operating system utilities or RMAN and use either tool to restore them. |
| implicit query | 隐式查询 | A component of a DML statement that retrieves data without a subquery. An UPDATE, DELETE, or MERGE statement that does not explicitly include a SELECT statement uses an implicit query to retrieve the rows to be modified. |
| in-doubt distributed transaction | 可疑分布式事务 | A distributed transaction in which a two-phase commit is interrupted by any type of system or network failure. |
| in-flight transaction | 正在运行中的事务 | A transaction that is running when an outage breaks the connection between a client application and the database. |
| inactive online redo log file | 非活动在线重做日志文件 | An online redo log file that is not required for instance recovery. |
| inconsistent backup | 不一致备份 | A backup in which some files in the backup contain changes made after the checkpoint. Unlike a consistent backup, an inconsistent backup requires media recovery to be made consistent. |
| incremental-forever backup strategy | 永久备份增量 | The strategy in which an initial level 0 backup is taken to the Recovery Appliance, with all subsequent incremental backups occurring at level 1. The Recovery Appliance creates a virtual full backup by combining the initial level 0 with subsequent level 1 backups. |
| incremental refresh | 增量刷新 | A refresh that processes only the changes to the existing data in a materialized view. This method eliminates the need for a complete refresh. |
| index | 索引 | Optional schema object associated with a nonclustered table, table partition, or table cluster. In some cases indexes speed data access. |
| index block | 索引数据块 | A special type of data block that manages space differently from table blocks. |
| index cluster | 索引簇 | An table cluster that uses an index to locate data. The cluster index is a B-tree index on the cluster key. |
| index clustering factor | 索引簇因子 | A measure of the row order in relation to an indexed value such as last name. The more order that exists in row storage for this value, the lower the clustering factor. |
| index-organized table | 索引表 | A table whose storage organization is a variant of a primary B-tree index. Unlike a heap-organized table, data is stored in primary key order. |