Master-Slave Streaming Replication
流复制：就是从库通过tcp流从主库中同步相应的数据。
主:称为 primary
从:称为 stand_by
GreenPlum集群 ，简称 GP
Postgres-XC集群 简称 XC
Postgresql 单数据库实例, 简称pgsql
hot backup
是数据库运行的情况下，采用archivelog mode(归档模式) 方式备份数据库的方法。
热备份要求数据库在Archivelog()方式下操作，并需要大量的档案空间。一旦
数据库运行在archivelog状态下，就可以做备份了。
cold backup
也被称为离线备份，是指在关闭 数据库并且数据库不能更新的状况下进行的数据库完整备份。
archivelog mode : archive mode, log archive mode, archive mode,
a、可以通过设置数据库在归档模式下来自动保存日志文件
b、您可以在数据库建立后执行 ALTER DATABASE 指令将
数据库切换为「封存模式」(ARCHIVELOG mode)。
High Availability
Usually used to describe a system that has been specifically designed to reduce downtime while maintaining high availability of its services
The principle of high availability guarantee is "clustering", or "redundancy", there is only one single point, the service will be affected if it fails; if there are redundant backups, there are other backups that can be topped up.
With redundancy, it is not enough. Every time a failure occurs, manual intervention is required to restore the system, which will inevitably increase the unserviceable practice of the system. Therefore, the high availability of the system is achieved through "automatic failover".
Pacemaker
is a cluster resource manager. It leverages the messaging and membership management capabilities provided by cluster infrastructure (OpenAIS, heartbeat, or corosync) to detect and recover from node or resource level failures for maximum availability of cluster services (aka resources). ,
Corosync
It is a part of the cluster management suite. It can define the method and protocol of information transmission through a simple configuration file when transmitting information.
Failover: Failover
Distributed database
Distributed Cloud Database (DCDB) is a high-performance database service that supports automatic horizontal splitting—that is, the business feels a complete logical table, but the data is evenly split into multiple physical shards, which can effectively solve the problem of large Concurrent, ultra-high-performance, and ultra-large-capacity OLTP scenarios; each shard of DCDB adopts a master-slave high-availability architecture by default, providing a complete set of solutions such as elastic expansion, backup, recovery, monitoring, etc., to effectively solve the problems of rapid business development for you. Database performance bottlenecks allow you to focus more on business development.