pgpool 的安装之一

os: centos7.4
postgresql:9.6.8
pgpool:3.7.3

pgpool 简介

准确的名字是Pgpool-II，这里简称为pgpool。pgpool 是介于postgresql 服务和 postgresql 客户端的中间件。它提供如下功能：
1、连接池
2、复制
3、负载均衡
4、限制超过限度的连接
5、并行查询

具有如下工作模式：
1、原始模式
2、连接池模式
3、复制模式
4、主/备模式
5、并行模式

其中，主/备模式 + postgresql stream 是目前最流行的模式。

下载

pgpool的下载地址：
http://www.pgpool.net/
http://www.pgpool.net/mediawiki/index.php/Downloads
pgpool的文档地址：
http://www.pgpool.net/docs/latest/en/html/
http://www.pgpool.net/docs/latest/en/html/install-requirements.html

本次用编译pgpool-II-3.7.3.tar.gz的方式来做
看了文档后发现有几个产品 pgpool-II，pgpoolAdmin，pgpool-II repository，pgpool-HA，后面有空再研究下。

ip 规划如下

pgpool    192.168.56.100

pgsql1    192.168.56.101
pgsql2    192.168.56.102

安装配置pgsql1、pgsql2节点的master/slave

在节点pgsql1、pgsql2使用yum安装 postgresql 9.6.8，配置好 stream
参考 https://www.postgresql.org/download/linux/redhat/
配置成功后，可以在master上看到连接进来的salve

postgres=# select * from pg_stat_replication;
-[ RECORD 1 ]----+------------------------------
pid              | 6984
usesysid         | 16384
usename          | replicator
application_name | walreceiver
client_addr      | 192.168.56.102
client_hostname  |
client_port      | 50309
backend_start    | 2018-05-14 23:49:03.598043+08
backend_xmin     |
state            | streaming
sent_location    | 0/3000060
write_location   | 0/3000060
flush_location   | 0/3000060
replay_location  | 0/3000060
sync_priority    | 0
sync_state       | async

sync_state = async 表示是异步复制

安装psql

pgpool节点安装psql客户端，主要是要使用到libpq

[root@pgpool ~]# yum install https://download.postgresql.org/pub/repos/yum/9.6/redhat/rhel-7-x86_64/pgdg-centos96-9.6-3.noarch.rpm
[root@pgpool ~]# yum install postgresql96 postgresql96-libs postgresql96-devel
[root@pgpool ~]# yum list installed|grep -i postgre
postgresql96.x86_64                9.6.9-1PGDG.rhel7                   @pgdg96
postgresql96-devel.x86_64          9.6.9-1PGDG.rhel7                   @pgdg96
postgresql96-libs.x86_64           9.6.9-1PGDG.rhel7                   @pgdg96

编译安装

pgpool节点操作，编译安装三把斧。

# groupadd postgres
# useradd -g postgres postgres
# mkdir -p /usr/pgpool/pgpool3.7.3
# chown -R postgres:postgres  /usr/pgpool

# vi /home/postgres/.bash_profile
export PGHOME=/usr/pgsql-9.6
#export PGDATA=/var/lib/pgsql/9.6/data

export LD_LIBRARY_PATH=$PGHOME/lib
export LD_LIBRARY_PATH=${LD_LIBRARY_PATH}:/lib:/usr/lib:/usr/local/lib
export LD_LIBRARY_PATH=${LD_LIBRARY_PATH}:/usr/pgpool/pgpool3.7.3/lib

export PATH=$PGHOME/bin:$PATH
export PATH=/usr/pgpool/pgpool3.7.3/bin:$PATH

# su - postgres
$ cd /tmp
$ rz
$ tar -zxvf /tmp/pgpool-II-3.7.3.tar.gz
$ cd pgpool-II-3.7.3/
$ ./configure --prefix=/usr/pgpool/pgpool3.7.3 -with-pgsql=/usr/pgsql-9.6 --with-openssl 
$ make
$ make install
$ cd /usr/pgpool/pgpool3.7.3
$ ls -l
total 4
drwxrwxr-x. 2 postgres postgres 4096 May 15 03:03 bin
drwxrwxr-x. 2 postgres postgres  227 May 15 03:03 etc
drwxrwxr-x. 2 postgres postgres   90 May 15 03:03 include
drwxrwxr-x. 2 postgres postgres   98 May 15 03:03 lib
drwxrwxr-x. 3 postgres postgres   23 May 15 03:03 share

–configure 错误
checking for PQexecPrepared in -lpq… noconfigure: error: libpq is not installed or libpq is old
备注：如果出现这个错误，说明找不到 PostgreSQL lib 库， configure 加上 -with-pgsql 选项。

安装 pgpool 相关函数

pgpool 函数非必需安装，但强烈建议安装 pgpool_adm, pgpool_regclass, pgpool_recovery 函数 。
官方文档是这样说的 pgpool_adm is an extension and should be installed on all PostgreSQL servers
pgpool节点上操作

# source /home/postgres/.bash_profile
# cd /tmp/pgpool-II-3.7.3/src/sql
# make
# make install

# cd /usr/pgsql-9.6/share/extension
# ls -l
total 32
-rw-r--r--. 1 root root 2574 May 15 03:14 pgpool_adm--1.0.sql
-rw-r--r--. 1 root root  146 May 15 03:14 pgpool_adm.control
-rw-r--r--. 1 root root 1002 May 15 03:14 pgpool_recovery--1.1.sql
-rw-r--r--. 1 root root  178 May 15 03:14 pgpool_recovery.control
-rw-r--r--. 1 root root  557 May 15 03:14 pgpool-recovery.sql
-rw-r--r--. 1 root root  283 May 15 03:14 pgpool_regclass--1.0.sql
-rw-r--r--. 1 root root  152 May 15 03:14 pgpool_regclass.control
-rw-r--r--. 1 root root  142 May 15 03:14 pgpool-regclass.sql

# cd /usr/pgsql-9.6/lib
# ls -l |grep -i pgpool
-rwxr-xr-x. 1 root root   66104 May 15 03:14 pgpool_adm.so
-rwxr-xr-x. 1 root root   46160 May 15 03:14 pgpool-recovery.so
-rwxr-xr-x. 1 root root   29568 May 15 03:14 pgpool-regclass.so

$ cd /usr/pgpool/pgpool3.7.3/lib
$ ls -l
total 488
-rw-r--r--. 1 postgres postgres 302534 May 15 03:03 libpcp.a
-rwxr-xr-x. 1 postgres postgres    987 May 15 03:03 libpcp.la
lrwxrwxrwx. 1 postgres postgres     15 May 15 03:03 libpcp.so -> libpcp.so.1.0.0
lrwxrwxrwx. 1 postgres postgres     15 May 15 03:03 libpcp.so.1 -> libpcp.so.1.0.0
-rwxr-xr-x. 1 postgres postgres 189472 May 15 03:03 libpcp.so.1.0.0

在pgsql1、pgsql2 同样也要编译C语言函数,或者从pgpool拷贝上面3类文件到pgsql1、pgsql2

# source /var/lib/pgsql/.bash_profile
# mkdir -p /usr/pgpool/pgpool3.7.3/lib
# cd /tmp
# rz
# tar -zxvf ./pgpool-II-3.7.3.tar.gz
# cd /tmp/pgpool-II-3.7.3/src/sql
# ls -l
total 8
-rw-rw-r-- 1 root root  617 Apr 17 16:54 insert_lock.sql
-rw-rw-r-- 1 root root 1407 Apr 17 16:54 Makefile
drwxrwxr-x 2 root root  179 May 15 10:29 pgpool_adm
drwxrwxr-x 2 root root  255 May 15 10:27 pgpool-recovery
drwxrwxr-x 2 root root  255 May 15 10:27 pgpool-regclass

# make
# make install

处理pgpool-recovery、pgpool-regclass没没错误，但是pgpool_adm报错了。错误如下：
make -C pgpool_adm all
make[1]: Entering directory /tmp/pgpool-II-3.7.3/src/sql/pgpool_adm'
gcc -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Wendif-labels -Wmissing-format-attribute -Wformat-security -fno-strict-aliasing -fwrapv -fexcess-precision=standard -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -m64 -mtune=generic -fPIC -shared -o pgpool_adm.so pgpool_adm.o -L/usr/pgsql-9.6/lib -Wl,--as-needed -L/usr/lib64 -Wl,--as-needed -Wl,-rpath,'/usr/pgsql-9.6/lib',--enable-new-dtags -L../../libs/pcp/.libs -lpcp -Wl,--as-needed -Wl,-rpath,'/usr/local/lib',--enable-new-dtags
/usr/bin/ld: cannot find -lpcp
collect2: error: ld returned 1 exit status
make[1]: *** [pgpool_adm.so] Error 1
make[1]: Leaving directory/tmp/pgpool-II-3.7.3/src/sql/pgpool_adm’
make: * [all-pgpool_adm-recurse] Error 2

/usr/bin/ld: cannot find -lpcp 通过完全编译 pgpool来解决。

pgsql1(master)节点上操作，在 template1 上创建extension;

template1=# create extension pgpool_adm;
CREATE EXTENSION
template1=# create extension pgpool_regclass;
CREATE EXTENSION
template1=# create extension pgpool_recovery;
CREATE EXTENSION
template1=# 
template1=# df+
 Schema |        Name         | Result data type |                                          Argument data types                                          |  Type  | Volatility | Parallel |  Owner   | Security | Access privileges | Language |     Source code     | Description 
--------+---------------------+------------------+-------------------------------------------------------------------------------------------------------+--------+------------+----------+----------+----------+-------------------+----------+---------------------+-------------
 public | pcp_attach_node     | boolean          | integer, text, integer, text, text, OUT node_attached boolean                                         | normal | volatile   | unsafe   | postgres | invoker  |                   | c        | _pcp_attach_node    | 
 public | pcp_attach_node     | boolean          | integer, text, OUT node_attached boolean                                                              | normal | volatile   | unsafe   | postgres | invoker  |                   | c        | _pcp_attach_node    | 
 public | pcp_detach_node     | boolean          | integer, boolean, text, integer, text, text, OUT node_detached boolean                                | normal | volatile   | unsafe   | postgres | invoker  |                   | c        | _pcp_detach_node    | 
 public | pcp_detach_node     | boolean          | integer, boolean, text, OUT node_detached boolean                                                     | normal | volatile   | unsafe   | postgres | invoker  |                   | c        | _pcp_detach_node    | 
 public | pcp_node_count      | integer          | text, integer, text, text, OUT node_count integer                                                     | normal | volatile   | unsafe   | postgres | invoker  |                   | c        | _pcp_node_count     | 
 public | pcp_node_count      | integer          | text, OUT node_count integer                                                                          | normal | volatile   | unsafe   | postgres | invoker  |                   | c        | _pcp_node_count     | 
 public | pcp_node_info       | record           | integer, text, integer, text, text, OUT host text, OUT port integer, OUT status text, OUT weight real | normal | volatile   | unsafe   | postgres | invoker  |                   | c        | _pcp_node_info      | 
 public | pcp_node_info       | record           | integer, text, OUT host text, OUT port integer, OUT status text, OUT weight real                      | normal | volatile   | unsafe   | postgres | invoker  |                   | c        | _pcp_node_info      | 
 public | pcp_pool_status     | record           | text, integer, text, text, OUT item text, OUT value text, OUT description text                        | normal | volatile   | unsafe   | postgres | invoker  |                   | c        | _pcp_pool_status    | 
 public | pcp_pool_status     | record           | text, OUT item text, OUT value text, OUT description text                                             | normal | volatile   | unsafe   | postgres | invoker  |                   | c        | _pcp_pool_status    | 
 public | pgpool_pgctl        | boolean          | action text, stop_mode text                                                                           | normal | volatile   | unsafe   | postgres | invoker  |                   | c        | pgpool_pgctl        | 
 public | pgpool_recovery     | boolean          | script_name text, remote_host text, remote_data_directory text                                        | normal | volatile   | unsafe   | postgres | invoker  |                   | c        | pgpool_recovery     | 
 public | pgpool_recovery     | boolean          | script_name text, remote_host text, remote_data_directory text, remote_port text                      | normal | volatile   | unsafe   | postgres | invoker  |                   | c        | pgpool_recovery     | 
 public | pgpool_remote_start | boolean          | remote_host text, remote_data_directory text                                                          | normal | volatile   | unsafe   | postgres | invoker  |                   | c        | pgpool_remote_start | 
 public | pgpool_switch_xlog  | text             | arcive_dir text                                                                                       | normal | volatile   | unsafe   | postgres | invoker  |                   | c        | pgpool_switch_xlog  | 
(15 rows)


template1=# df
                                                                        List of functions
 Schema |        Name         | Result data type |                                          Argument data types                                          |  Type  
--------+---------------------+------------------+-------------------------------------------------------------------------------------------------------+--------
 public | pcp_attach_node     | boolean          | integer, text, integer, text, text, OUT node_attached boolean                                         | normal
 public | pcp_attach_node     | boolean          | integer, text, OUT node_attached boolean                                                              | normal
 public | pcp_detach_node     | boolean          | integer, boolean, text, integer, text, text, OUT node_detached boolean                                | normal
 public | pcp_detach_node     | boolean          | integer, boolean, text, OUT node_detached boolean                                                     | normal
 public | pcp_node_count      | integer          | text, integer, text, text, OUT node_count integer                                                     | normal
 public | pcp_node_count      | integer          | text, OUT node_count integer                                                                          | normal
 public | pcp_node_info       | record           | integer, text, integer, text, text, OUT host text, OUT port integer, OUT status text, OUT weight real | normal
 public | pcp_node_info       | record           | integer, text, OUT host text, OUT port integer, OUT status text, OUT weight real                      | normal
 public | pcp_pool_status     | record           | text, integer, text, text, OUT item text, OUT value text, OUT description text                        | normal
 public | pcp_pool_status     | record           | text, OUT item text, OUT value text, OUT description text                                             | normal
 public | pgpool_pgctl        | boolean          | action text, stop_mode text                                                                           | normal
 public | pgpool_recovery     | boolean          | script_name text, remote_host text, remote_data_directory text                                        | normal
 public | pgpool_recovery     | boolean          | script_name text, remote_host text, remote_data_directory text, remote_port text                      | normal
 public | pgpool_remote_start | boolean          | remote_host text, remote_data_directory text                                                          | normal
 public | pgpool_switch_xlog  | text             | arcive_dir text                                                                                       | normal
(15 rows)

有几个关键的配置文件
pcp.conf 用于管理查、看节点信息，如加入新节点。该文件主要是存储用户名及md5形式的密码。
pgpool.conf 用于设置pgpool的模式，主次数据库的相关信息等。
pool_hba.conf 用于认证用户登录方式，如客户端IP限制等，类似于postgresql的pg_hba.conf文件。
pool_passwd 用于保存相应客户端登录帐号名及md5密码。

pgsql1、pgsql2上赋予命令执行权限

# chmod u+s /sbin/ifconfig
# chmod u+s /usr/sbin/

pgpool上配置ssh免密登录

$ ssh-keygen
$ ssh-copy-id postgres@pgpool
$ ssh-copy-id postgres@pgsql1
$ ssh-copy-id postgres@pgsql2
$ ssh postgres@pgpool
$ ssh postgres@pgsql1
$ ssh postgres@pgsql2
$ exit

pgsql1上配置ssh免密登录

$ ssh-keygen
$ ssh-copy-id postgres@pgsql1
$ ssh-copy-id postgres@pgsql2
$ ssh postgres@pgsql1
$ ssh postgres@pgsql2
$ exit

pgsql2上配置ssh免密登录

$ ssh-keygen
$ ssh-copy-id postgres@pgsql1
$ ssh-copy-id postgres@pgsql2
$ ssh postgres@pgsql1
$ ssh postgres@pgsql2
$ exit

配置 pcp.conf

pgpool节点上配置 pcp.conf，用户pgpool的管理员账号维护

$ cd /usr/pgpool/pgpool3.7.3/etc
$ cp pcp.conf.sample pcp.conf
$ pg_md5 -u pgpool -p
password:
f24aeb1c3b7d05d7eaf2cd648c307092

$ cd /usr/pgpool/pgpool3.7.3/etc
$ vi pcp.conf
pgpool:f24aeb1c3b7d05d7eaf2cd648c307092

配置 pool_hba.conf

pgpool节点上配置 pool_hba.conf

$ vi pool_hba.conf

host    all         all         192.168.56.0/24       md5
host    all         all         10.0.2.0/24           md5

配置 pgpool.conf

pgpool节点上配置 pgpool.conf，该文件是一个关键的配置文件。

$ cd /usr/pgpool/pgpool3.7.3/etc
$ ls -l
total 196
-rw-r--r--. 1 postgres postgres   898 May 15 03:53 pcp.conf
-rw-r--r--. 1 postgres postgres   858 May 15 03:03 pcp.conf.sample
-rw-r--r--. 1 postgres postgres 35840 May 15 03:03 pgpool.conf.sample
-rw-r--r--. 1 postgres postgres 35313 May 15 03:03 pgpool.conf.sample-logical
-rw-r--r--. 1 postgres postgres 35468 May 15 03:03 pgpool.conf.sample-master-slave
-rw-r--r--. 1 postgres postgres 35428 May 15 03:03 pgpool.conf.sample-replication
-rw-r--r--. 1 postgres postgres 35490 May 15 03:03 pgpool.conf.sample-stream
-rw-r--r--  1 postgres postgres  3319 May 15 05:09 pool_hba.conf
-rw-r--r--. 1 postgres postgres  3260 May 15 03:03 pool_hba.conf.sample

Operation mode              Configuration file name
Streaming replication mode  pgpool.conf.sample-stream
Replication mode            pgpool.conf.sample-replication
Master slave mode           pgpool.conf.sample-master-slave
Raw mode                    pgpool.conf.sample
Logical replication mode    pgpool.conf.sample-logical

pgpool有几个模式

功能/模式 原始模式(*3) 复制模式 主/备模式 并行查询模式
连接池      X           O        O        O
复制        X           O        X       (*1)
负载均衡    X           O        O        (*1)
故障恢复    O           O        O        X
在线恢复    X           O       (*2)      X
并行查询    X           X        X        O
需要的
服务器数  1 或更多    2 或更多  2 或更多  2 或更多
是否需要
系统数据库  否          否       否        是

O 意味着“可用”， X 意味着“不可用 
(*1) 并行查询模式需要同时打开复制和负载均衡，但是复制和负载均衡无法用于并行查询模式中的分布式表。 
(*2) 在线恢复可以和流复制同时使用。 
(*3) 客户端仅仅是通过 pgpool-II 连接到 PostgreSQL 服务器。这种模式仅仅用于限制到服务器的连接数，或者在多台机器上启用故障恢复。 

采用pgpool master/slave + postgresql stream模式，这里只是简单列出一些关键参数，后面会针对每种工作模式详细测试。

$ cp pgpool.conf.sample-stream pgpool.conf
$ vi pgpool.conf

replication_mode = off
master_slave_mode = on
master_slave_sub_mode = 'stream'
load_balance_mode = on

启动pgpool

$ which pgpool
/usr/pgpool/pgpool3.7.3/bin/pgpool
$ pgpool --help
pgpool-II version 3.7.3 (amefuriboshi),
  A generic connection pool/replication/load balance server for PostgreSQL

Usage:
  pgpool [ -c] [ -f CONFIG_FILE ] [ -F PCP_CONFIG_FILE ] [ -a HBA_CONFIG_FILE ]
         [ -n ] [ -D ] [ -d ]
  pgpool [ -f CONFIG_FILE ] [ -F PCP_CONFIG_FILE ] [ -a HBA_CONFIG_FILE ]
         [ -m SHUTDOWN-MODE ] stop
  pgpool [ -f CONFIG_FILE ] [ -F PCP_CONFIG_FILE ] [ -a HBA_CONFIG_FILE ] reload

Common options:
  -a, --hba-file=HBA_CONFIG_FILE
                      Set the path to the pool_hba.conf configuration file
                      (default: /usr/pgpool/pgpool3.7.3/etc/pool_hba.conf)
  -f, --config-file=CONFIG_FILE
                      Set the path to the pgpool.conf configuration file
                      (default: /usr/pgpool/pgpool3.7.3/etc/pgpool.conf)
  -F, --pcp-file=PCP_CONFIG_FILE
                      Set the path to the pcp.conf configuration file
                      (default: /usr/pgpool/pgpool3.7.3/etc/pcp.conf)
  -h, --help          Print this help

Start options:
  -C, --clear-oidmaps Clear query cache oidmaps when memqcache_method is memcached
                      (If shmem, discards whenever pgpool starts.)
  -n, --dont-detach   Don't run in daemon mode, does not detach control tty
  -x, --debug-assertions   Turns on various assertion checks, This is a debugging aid
  -D, --discard-status Discard pgpool_status file and do not restore previous status
  -d, --debug         Debug mode

Stop options:
  -m, --mode=SHUTDOWN-MODE
                      Can be "smart", "fast", or "immediate"

Shutdown modes are:
  smart       quit after all clients have disconnected
  fast        quit directly, with proper shutdown
  immediate   the same mode as fast

$ pgpool -a /usr/pgpool/pgpool3.7.3/etc/pool_hba.conf -f /usr/pgpool/pgpool3.7.3/etc/pgpool.conf -F /usr/pgpool/pgpool3.7.3/etc/pcp.conf > /tmp/pgpool.log 2>&1 &

调试用使用 -n -d
$ pgpool -a /usr/pgpool/pgpool3.7.3/etc/pool_hba.conf -f /usr/pgpool/pgpool3.7.3/etc/pgpool.conf -F /usr/pgpool/pgpool3.7.3/etc/pcp.conf -n -d

-n 非 linux deamon方式
-d debug模式

$ ps -ef|grep -i pool
avahi      670     1  0 04:29 ?        00:00:00 avahi-daemon: running [pgpool.local]
postgres  3633     1  1 06:34 ?        00:00:00 pgpool
postgres  3638  3633  0 06:34 ?        00:00:00 pgpool: wait for connection request
postgres  3639  3633  0 06:34 ?        00:00:00 pgpool: wait for connection request
postgres  3640  3633  0 06:34 ?        00:00:00 pgpool: wait for connection request
postgres  3641  3633  0 06:34 ?        00:00:00 pgpool: wait for connection request
postgres  3642  3633  0 06:34 ?        00:00:00 pgpool: wait for connection request
postgres  3643  3633  0 06:34 ?        00:00:00 pgpool: wait for connection request

# netstat -antp |grep -i "0.0.0.0"
tcp        0      0 0.0.0.0:9999            0.0.0.0:*               LISTEN      3633/pgpool
tcp        0      0 0.0.0.0:111             0.0.0.0:*               LISTEN      1/systemd
tcp        0      0 192.168.122.1:53        0.0.0.0:*               LISTEN      1215/dnsmasq
tcp        0      0 0.0.0.0:22              0.0.0.0:*               LISTEN      970/sshd
tcp        0      0 127.0.0.1:631           0.0.0.0:*               LISTEN      969/cupsd
tcp        0      0 127.0.0.1:25            0.0.0.0:*               LISTEN      1129/master
tcp        0      0 0.0.0.0:9898            0.0.0.0:*               LISTEN      3633/pgpool

pgpool的使用

postgresql的primary server和standby server跑起来后，我们就可以使用pgpool来观察和操作了：

pgsql1(master) 上创建用户和数据库

postgres=# create user peiyb with password 'peiybpeiyb';
CREATE ROLE
postgres=# create database peiybdb owner = peiyb;
CREATE DATABASE

连接pgpool

$ pg_md5 -h
$ pg_md5 -m -p -u peiyb
$ cat pool_passwd
peiyb:md5bd0875843854575a4b7328813ea498cb

$ psql -h 192.168.56.100 -p 9999 -d peiybdb -U peiyb
Password for user peiyb:
psql (9.6.9)
Type "help" for help.

peiybdb=>
peiybdb=> show pool_version;
     pool_version     
----------------------
 3.7.3 (amefuriboshi)
(1 row)

peiybdb=> show pool_nodes;
 node_id | hostname | port | status | lb_weight |  role   | select_cnt | load_balance_node | replication_delay 
---------+----------+------+--------+-----------+---------+------------+-------------------+-------------------
 0       | pgsql1   | 5432 | up     | 0.500000  | primary | 0          | false             | 0
 1       | pgsql2   | 5432 | up     | 0.500000  | standby | 0          | true              | 0
(2 rows)

一些命令的描述

Table of Contents
PGPOOL SHOW -- show the value of a configuration parameter
PGPOOL SET -- change a configuration parameter
PGPOOL RESET -- restore the value of a configuration parameter to the default value
SHOW POOL STATUS --  sends back the list of configuration parameters with their name, value, and description
SHOW POOL NODES --  sends back a list of all configured nodes
SHOW POOL_PROCESSES --  sends back a list of all Pgpool-II processes waiting for connections and dealing with a connection
SHOW POOL_POOLS --  sends back a list of pools handled by Pgpool-II.
SHOW POOL_VERSION --  displays a string containing the Pgpool-II release number.
SHOW POOL_CACHE --  displays cache storage statistics