##Postgres-XL is composed of three major components: the GTM (Global Transaction Manager), the Coordinator and the Datanode. Their features are given in the following sections.html
###GTM (Global Transaction Manager) ####The GTM is a key component of Postgres-XL to provide consistent transaction management and tuple visibility control. As described later in this manual, PostgreSQL's transaction management is based upon MVCC (Multi-Version Concurrency Control) technology. Postgres-XL extracts this technology into separate component such as the GTM so that any Postgres-XL component's transaction management is based upon single global status. Details will be described in Chapter 50.node
###Coordinator ####The Coordinator is an interface to the database for applications. It acts like a conventional PostgreSQL backend process, however the Coordinator does not store any actual data. The actual data is stored by the Datanodes as described below. The Coordinator receives SQL statements, gets Global Transaction Id and Global Snapshots as needed, determines which Datanodes are involved and asks them to execute (a part of) statement. When issuing statement to Datanodes, it is associated with GXID and Global Snapshot so that Multi-version Concurrency Control (MVCC) properties extend cluster-wide.sql
###Datanode ####The Datanode actually stores user data. Tables may be distributed among Datanodes, or replicated to all the Datanodes. The Datanode does not have a global view of the whole database, it just takes care of locally stored data. Incoming statements are examined by the Coordinator as described next, and subplans are made. These are then transferred to each Datanode involved together with a GXID and Global Snapshot as needed. The datanode may receive request from various Coordinators in separate sessions. However, because each transaction is identified uniquely and associated with a consistent (global) snapshot, each Datanode can properly execute in its transaction and snapshot context. ###本地起pgsql mac os 参考https://www.jianshu.com/p/10ced5145d39 ###设定方案 1 GTM 2 Datanode Coordinator和GTM装在Datanode节点上 ##安装步骤 默认在所有机器使用下列命令 ###先更改每台机器的hosts vim /etc/hosts/ ###关闭防火墙以后 重启机器 ufw disable/enable ###添加新的数据库用户数据库
useradd pgsqlname passwd pgspasswd
###将新建用户添加sudo权限vim
su - visudo
在最后加上一行保存退出 usrname ALL=(ALL) ALL 以后在/home路径建立usrname文件夹，进入之后建立ssh免密链接，在GTM节点使用下列命令session
su - usrname ssh-keygen -t rsa #选取路径为用户名下.ssh文件夹 密码设定为空
http://www.ruanyifeng.com/blog/2013/12/getting_started_with_postgresql.html