• Database instance: a virtualized database server that consists of high-speed buffer pools and backend processes.
  • On-premises database instance: a database instance that is deployed in a non-cloud environment, such as a data center.
  • ECS-based self-managed database instance: a self-managed database instance that is deployed on an Elastic Compute Service (ECS) instance.
  • Cluster: a collection of one or more database instances that run the same database engine, such as MySQL, Oracle, or SQL Server. A database instance belongs to only one cluster.
  • Database gateway: a daemon process that is deployed in the same environment as databases. A database gateway collects and computes performance data. A database gateway does not collect business data. Before a database gateway transmits data, the database gateway encrypts and compresses the data. For more information, see Database gateway overview.
  • Index: In a relational database, an index is a unique and physical data structure that sorts data in one or more columns. An index is a collection of data that is copied from one or more columns in a table and provides logical pointers that point to the physical locations of specific data in the table. Indexes help improve the speed of data queries.