PostgreSQL操作随记

PostgreSQL默认用户: postgres

Connect

psql -h host -U user -W

backup tools

pg_dump

PGPASSWORD="12345" pg_dump

pg_dumpall

需要注意导出的文件格式(using pg_dump -Fc generates the most flexible export format and is already compressed)

ps:

• 五花八门的传递password值的方法: how-to-pass-in-password-to-pg-dump
• pg_restore 需要关注的 why pg_restore ignores --create ? Error: failed: FATAL: database "new_db" does not exist
  • The -d will restore in the given database if and only if -C is not used. If -C is used, the database is used as a "launchpad", not as the destination.

连接数相关

配置文件

sed  "s/max_connections = .*/max_connections = 1024/" /var/lib/postgresql/data/postgresql.conf|grep max_connection

sed -i "s/max_connections = .*/max_connections = 1024/" /var/lib/postgresql/data/postgresql.conf|grep max_connection

commands

临时修改连接数(待验证)

alter system set max_connections=1024

查看连接数

select count(1) from pg_stat_activity;

查看最大连接数值

show max_connections;

查看保留连接数

show superuser_reserved_connections;

查看连接的客户端信息

SELECT * FROM pg_stat_activity

keywords: PSQLException: FATAL: sorry, too many clients already

common commands

show databases in psql

SELECT datname FROM pg_database;

desc table in psql

postgres=# \c keel
You are now connected to database "keel" as user "postgres".
keel=# \dt
                List of relations
 Schema |         Name         | Type  |  Owner
--------+----------------------+-------+----------
 public | app_permissions      | table | postgres
 public | app_versions         | table | postgres
 public | applications         | table | postgres
(30 rows)

keel=# \dt+
                              List of relations
 Schema |         Name         | Type  |  Owner   |    Size    | Description
--------+----------------------+-------+----------+------------+-------------
 public | app_permissions      | table | postgres | 8192 bytes |
 public | app_versions         | table | postgres | 72 kB      |
 public | applications         | table | postgres | 8192 bytes |
(30 rows)

enabling expanded display (like mysql \G)

# \x
Expanded display is on.
# \x
Expanded display is off.

run this for a single command by using the \x\g\x suffix to toggle expanded display on, run the query, then toggle it off again.

select * from foo \x\g\x

Note the lack of ; in the above line, this is intentional.