postgres-xl是个好东西？为什么呢？
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postgres-xl基于postgresql数据库, postgres可以吊打很多数据库.
它可以搞oltp, 抗衡MySQL, mysql没有分析函数功能
它可以搞oltp, 抗衡oracle, oracle生态弱, 没法实时
它对json支持好, 抗衡MongoDB, mongodb用得人越来越少了。。。
它还恐怖地支持各种语言扩展, java, javascript, r, python, haskell。。。
并且开源免费，简单强大的没朋友。。。
postgres-xl是postgresql MPP集群版, 继续吊打大数据数据库...
它比greenpulm版本新: 它跟greenpulm本是一家人，都是MPP架构的postgresql集群
但是原生改造, 版本基本上与postgresql一致, greenpulm的版本升不动啊。。。
它比oracle RAC/Teradata便宜，免费使用
它比hadoop省资源，没有GC，基于C语言资源利用率高，并且生态圈丰富，可视化方便
它出道早，版本稳定性强。
既然这么优秀，那么我们简单介绍一下,尤其是它在大数据方面的应用
postgres-xl分为以下组件:
a. gtm 负责全局事务
b. coordinator 处理分发执行
c. datanode 负责底层处理
datanode跟coordinator都 连接到gtm，
客户端连接到coordinator运行sql,
coordinator使用gtm进行一些事务功能分发给datanode执行
大数据的发展方向
什么是MPP？
MPP (Massively Parallel Processing)，即大规模并行处理，是分布式、并行、结构化数据库集群，具备高性能、高可用、高扩展特性，可以为超大规模数据管理提供高性价比的通用计算平台，广泛用于支撑各类数据仓库系统、BI 系统。
MPP架构特征：
•任务并行执行
•数据分布式存储(本地化)
•分布式计算
•横向扩展
思考对比
Oracle集群的特点：每个节点全量存储
Mysql热备的特点：主从，每个节点全量存储
MPP——分布式关系数据库
GreenPlum：基于Postgres XL 8.2进行封装，多年没升级过。
Mysql Cluster：刚出来两年，稳定性和性能比较差。
Postgres
XL 与 Postgres
LL ，是Postgresql数据库两种集群模式，Postgres
XL是当今主流MPP
Postgres XL集群架构
GTM：Global Transaction Manager
Coordinator：协调器
Datanode：数据节点
GTM-Proxy：GTM代理器
组件介绍
Global Transaction Monitor (GTM)
全局事务管理器，确保群集范围内的事务一致性。 GTM负责发放事务ID和快照作为其多版本并发控制的一部分。
集群可选地配置一个备用GTM（GTM Standby），以改进可用性。此外，可以在协调器间配置代理GTM， 可用于改善可扩展性，减少GTM的通信量。
GTM Standby
GTM的备节点，在pgxc,pgxl中，GTM控制所有的全局事务分配，如果出现问题，就会导致整个集群不可用，为了增加可用性，增加该备用节点。当GTM出现问题时，GTM Standby可以升级为GTM，保证集群正常工作。
GTM-Proxy
GTM需要与所有的Coordinators通信，为了降低压力，可以在每个Coordinator机器上部署一个GTM-Proxy。
Coordinator
协调员管理用户会话，并与GTM和数据节点进行交互。协调员解析，产生查询计划，并给语句中的每一个组件发送下一个序列化的全局性计划。
通常此服务和数据节点部署在一起。
正式安装
Note: 其实在生产环境，如果你集群的数量少于20台的话，甚至可以不需要使用gtm-proxy
#1)System Initialization Optimization on every nodes
cat >> /etc/security/limits.conf << EOF
* hard memlock unlimited
* soft memlock unlimited
* - nofile 65535
EOF
setenforce 0
sed -i 's/^SELINUX=.*$/SELINUX=disabled/' /etc/selinux/config
systemctl stop firewalld.service
systemctl disable firewalld.service
cat >/etc/hosts <>/etc/sudoers
######################################################################
#3)Configure ssh authentication to avoid inputing password for pgxc_ctl(run this commad on every nodes)
######################################################################
su - postgres
ssh-keygen -t rsa
cat ~/.ssh/id_rsa.pub >> ~/.ssh/authorized_keys
chmod 600 authorized_keys
cat ~/.ssh/id_rsa.pub | ssh neo4j01 'cat >> ~/.ssh/authorized_keys'
############################################
#4)Install dependency packages on every nodes#
############################################
sudo yum install -y flex bison readline-devel zlib-devel openjade docbook-style-dsssl gcc bzip2 e2fsprogs-devel uuid-devel libuuid-devel make wget
wget -c http://download.cashalo.com/schema/postgres-xl-9.5r1.6.tar.bz2 && tar jxf postgres-xl-9.5r1.6.tar.bz2
cd postgres-xl-9.5r1.6
./configure --prefix=/home/postgres/pgxl9.5 --with-uuid=ossp --with-uuid=ossp && make && make install && cd contrib/ && make && make install
#5)Configuring environment variables on every nodes
cat >>/home/postgres/.bashrc < Need to synchronize when original changed.
#---- GTM ------------------------------------------------------------------------------------
# GTM is mandatory. You must have at least (and only) one GTM master in your Postgres-XC cluster.
# If GTM crashes and you need to reconfigure it, you can do it by pgxc_update_gtm command to update
# GTM master with others. Of course, we provide pgxc_remove_gtm command to remove it. This command
# will not stop the current GTM. It is up to the operator.
#---- GTM Master -----------------------------------------------
#---- Overall ----
gtmName=gtm1
gtmMasterServer=neo4j01
gtmMasterPort=6666
gtmMasterDir=$pgxlDATA/gtm1
#---- Configuration ---
gtmExtraConfig=none # Will be added gtm.conf for both Master and Slave (done at initilization only)
gtmMasterSpecificExtraConfig=none # Will be added to Master's gtm.conf (done at initialization only)
#---- GTM Slave -----------------------------------------------
# Because GTM is a key component to maintain database consistency, you may want to configure GTM slave
# for backup.
#---- Overall ------
gtmSlave=y # Specify y if you configure GTM Slave. Otherwise, GTM slave will not be configured and
# all the following variables will be reset.
gtmSlaveName=gtm2
gtmSlaveServer=neo4j02 # value none means GTM slave is not available. Give none if you don't configure GTM Slave.
gtmSlavePort=6666 # Not used if you don't configure GTM slave.
gtmSlaveDir=$pgxlDATA/gtm2 # Not used if you don't configure GTM slave.
# Please note that when you have GTM failover, then there will be no slave available until you configure the slave
# again. (pgxc_add_gtm_slave function will handle it)
#---- Configuration ----
gtmSlaveSpecificExtraConfig=none # Will be added to Slave's gtm.conf (done at initialization only)
#---- GTM Proxy -------------------------------------------------------------------------------------------------------
# GTM proxy will be selected based upon which server each component runs on.
# When fails over to the slave, the slave inherits its master's gtm proxy. It should be
# reconfigured based upon the new location.
#
# To do so, slave should be restarted. So pg_ctl promote -> (edit postgresql.conf and recovery.conf) -> pg_ctl restart
#
# You don't have to configure GTM Proxy if you dont' configure GTM slave or you are happy if every component connects
# to GTM Master directly. If you configure GTL slave, you must configure GTM proxy too.
#---- Shortcuts ------
gtmProxyDir=$pgxlDATA/gtm_proxy
#---- Overall -------
gtmProxy=n # Specify y if you conifugre at least one GTM proxy. You may not configure gtm proxies
# only when you dont' configure GTM slaves.
# If you specify this value not to y, the following parameters will be set to default empty values.
# If we find there're no valid Proxy server names (means, every servers are specified
# as none), then gtmProxy value will be set to "n" and all the entries will be set to
# empty values.
#gtmProxyNames=(gtm_pxy1 gtm_pxy2 gtm_pxy3 gtm_pxy4) # No used if it is not configured
#gtmProxyServers=(neo4j01 neo4j02 neo4j03 neo4j04) # Specify none if you dont' configure it.
#gtmProxyPorts=(6660 6666 6666 6666) # Not used if it is not configured.
#gtmProxyDirs=($gtmProxyDir $gtmProxyDir $gtmProxyDir $gtmProxyDir) # Not used if it is not configured.
#---- Configuration ----
gtmPxyExtraConfig=none # Extra configuration parameter for gtm_proxy. Coordinator section has an example.
gtmPxySpecificExtraConfig=(none none none none)
#---- Coordinators ----------------------------------------------------------------------------------------------------
#---- shortcuts ----------
coordMasterDir=$pgxlDATA/coord
coordSlaveDir=$pgxlDATA/coord_slave
coordArchLogDir=$pgxlDATA/coord_archlog
#---- Overall ------------
coordNames=(coord1 coord2 coord3 coord4) # Master and slave use the same name
coordPorts=(5432 5432 5432 5432) # Master ports
poolerPorts=(6667 6667 6667 6667) # Master pooler ports
#coordPgHbaEntries=(192.168.29.0/24) # Assumes that all the coordinator (master/slave) accepts
coordPgHbaEntries=(0.0.0.0/0)
# the same connection
# This entry allows only $pgxcOwner to connect.
# If you'd like to setup another connection, you should
# supply these entries through files specified below.
# Note: The above parameter is extracted as "host all all 0.0.0.0/0 trust". If you don't want
# such setups, specify the value () to this variable and suplly what you want using coordExtraPgHba
# and/or coordSpecificExtraPgHba variables.
#coordPgHbaEntries=(::1/128) # Same as above but for IPv6 addresses
#---- Master -------------
coordMasterServers=(neo4j01 neo4j02 neo4j03 neo4j04) # none means this master is not available
coordMasterDirs=($coordMasterDir $coordMasterDir $coordMasterDir $coordMasterDir)
coordMaxWALsernder=0 # max_wal_senders: needed to configure slave. If zero value is specified,
# it is expected to supply this parameter explicitly by external files
# specified in the following. If you don't configure slaves, leave this value to zero.
coordMaxWALSenders=($coordMaxWALsernder $coordMaxWALsernder $coordMaxWALsernder $coordMaxWALsernder)
# max_wal_senders configuration for each coordinator.
#---- Slave -------------
coordSlave=n # Specify y if you configure at least one coordiantor slave. Otherwise, the following
# configuration parameters will be set to empty values.
# If no effective server names are found (that is, every servers are specified as none),
# then coordSlave value will be set to n and all the following values will be set to
# empty values.
#coordSlaveSync=y # Specify to connect with synchronized mode.
#coordSlaveServers=(node07 node08 node09 node06) # none means this slave is not available
#coordSlavePorts=(20004 20005 20004 20005) # Master ports
#coordSlavePoolerPorts=(20010 20011 20010 20011) # Master pooler ports
#coordSlaveDirs=($coordSlaveDir $coordSlaveDir $coordSlaveDir $coordSlaveDir)
#coordArchLogDirs=($coordArchLogDir $coordArchLogDir $coordArchLogDir $coordArchLogDir)
#---- Configuration files---
# Need these when you'd like setup specific non-default configuration
# These files will go to corresponding files for the master.
# You may supply your bash script to setup extra config lines and extra pg_hba.conf entries
# Or you may supply these files manually.
coordExtraConfig=coordExtraConfig # Extra configuration file for coordinators.
# This file will be added to all the coordinators'
# postgresql.conf
# Pleae note that the following sets up minimum parameters which you may want to change.
# You can put your postgresql.conf lines here.
cat > $coordExtraConfig <postgres-XL 下存在两种数据表，分别是replication表和distribute表
REPLICATION复制表：各个datanode节点中，表的数据完全相同，也就是说，插入数据时，会分别在每个datanode节点插入相同数据。读数据时，只需要读任意一个datanode节点上的数据。小表采用。
建表语法：
postgres=# create table rep(col1 int,col2 int)distribute by replication;
DISTRIBUTE表 ：会将插入的数据，按照拆分规则，分配到不同的datanode节点中存储，也就是sharding技术。每个datanode节点只保存了部分数据，通过coordinate节点可以查询完整的数据视图。分布式存储，大表采用，默认
postgres=# CREATE TABLE dist(col1 int, col2 int) DISTRIBUTE BY HASH(col1);
如何验证分布式存储？
分别插入100行数据：
postgres=# INSERT INTO rep SELECT generate_series(1,100), generate_series(101, 200);
postgres=# INSERT INTO dist SELECT generate_series(1,100), generate_series(101, 200);
psql -p 5432，通过Coordinater 访问查询完整的数据视图；
psql -p 5433，5433是Datanode的端口，此时只访问该单个节点
如何链接到指定的数据库呢？看下面的例子
psql -p 5432 aa ,aa为指定的库名，不指定时默认是postgres库，相当于hive里的default库
查询这个分布表数据在每个节点的分布：
postgres=# SELECT xc_node_id, count(*) FROM dist GROUP BY xc_node_id;
xc_node_id | count
------------+-------
-700122826 | 19
352366662 | 27
-560021589 | 23
823103418 | 31
(4 rows)
查询每个节点的ID信息
postgres=# select * from pgxc_node;
我们再来看看复制表
postgres=# select xc_node_id,count(*) from rep group by xc_node_id;
xc_node_id | count
------------+-------
-560021589 | 100
(1 row)
因为我们是在neo4j01节点上查询的，所以显示的id就是neo4j01节点的id；同理，如果我们是在其它节点查询的话那就显示其它节点的id。也就是说当我们查询复制表的时候，它只会走一个节点，不会走多个节点。针对这个特点，如果未来数据量很大，我们查询的时候，可以走负载均衡。
https://www.cnblogs.com/sfnz/p/7908380.html
Psql是PostgreSQL的一个命令行交互式客户端工具。PostgreSQL 一些命令、用法、语法，在Postgres xl集群都是通用的。
文章标题：postgres-XL集群安装
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