在我的rails app（v 3.2.8）中，到目前为止，我已经毫无问题地使用了迁移。
我使用PostgreSQL 9.2作为数据库。我调整了我的application.rb以使用sql而不是模式转储器（未注释config.active_record.schema_format = :sql）。
之后，我开始在迁移时遇到此错误：
$ rake db:migrate
[ALL MIGRATION STUFF IS PRINTED HERE]
pg_dump: [archiver (db)] connection to database "my_dev_db" failed: could not connect to server: Connection refused
Is the server running on host "localhost" (::1) and accepting
TCP/IP connections on port 5432?
could not connect to server: Connection refused
Is the server running on host "localhost" (127.0.0.1) and accepting
TCP/IP connections on port 5432?
could not connect to server: Connection refused
Is the server running on host "localhost" (fe80::1) and accepting
TCP/IP connections on port 5432?
rake aborted!
Error dumping database
I tried manually on the command line(logged in as the same user on my Mac)
<!-- language: lang-sh -->
$ pg_dump my_dev_db > /tmp/db.sql
No problems with that...happily dumps into `/tmp/db.sql`
Why is rails having trouble with `pg_dump`? (I am on Mac OSX Lion)
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Adding more diagnosis information
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$tail -10 /usr/local/var/postgres9.2/pg_hba.conf
local all all md5
# IPv4 local connections:
host all all 127.0.0.1/32 md5
# IPv6 local connections:
host all all ::1/128 md5
# Allow replication connections from localhost, by a user with the
# replication privilege.
#local replication rogert trust
#host replication rogert 127.0.0.1/32 trust
#host replication rogert ::1/128 trust
$ sudo lsof -p 62444 | awk '$5 == "unix" && $NF ~ /\// { print $NF }'
/tmp/.s.PGSQL.5432
$ ps auxw | grep post
postgres 1403 0.0 0.0 2435492 640 s007 S+ 21Oct12 0:00.05 bash
root 1401 0.0 0.0 2498096 128 s007 S 21Oct12 0:00.02 su postgres
rogert 62517 0.0 0.0 2426700 388 s001 R+ 9:21PM 0:00.00 grep post
rogert 62448 0.0 0.0 2481656 500 ?? Ss 8:46PM 0:00.03 postgres: wal writer process
rogert 62447 0.0 0.0 2481656 752 ?? Ss 8:46PM 0:00.07 postgres: writer process
rogert 62446 0.0 0.0 2481656 1040 ?? Ss 8:46PM 0:00.00 postgres: checkpointer process
rogert 62444 0.0 0.1 2481656 5368 s001 S 8:46PM 0:00.02 /usr/local/Cellar/postgresql/9.2.1/bin/postgres -D /usr/local/var/postgres9.2
$ rake db:migrate --trace
[ALL MIGRATION STUFF IS PRINTED HERE]
/Users/rogert/.rvm/gems/ruby-1.9.3-p194@rails_3.2.8/gems/activerecord-3.2.8/lib/active_record/railties/databases.rake:393:in `block (3 levels) in <top (required)>'
/Users/rogert/.rvm/gems/ruby-1.9.3-p194@rails_3.2.8/gems/rake-0.9.2.2/lib/rake/task.rb:205:in `call'
/Users/rogert/.rvm/gems/ruby-1.9.3-p194@rails_3.2.8/gems/rake-0.9.2.2/lib/rake/task.rb:205:in `block in execute'
/Users/rogert/.rvm/gems/ruby-1.9.3-p194@rails_3.2.8/gems/rake-0.9.2.2/lib/rake/task.rb:200:in `each'
/Users/rogert/.rvm/gems/ruby-1.9.3-p194@rails_3.2.8/gems/rake-0.9.2.2/lib/rake/task.rb:200:in `execute'
/Users/rogert/.rvm/gems/ruby-1.9.3-p194@rails_3.2.8/gems/rake-0.9.2.2/lib/rake/task.rb:158:in `block in invoke_with_call_chain'
/Users/rogert/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/monitor.rb:211:in `mon_synchronize'
/Users/rogert/.rvm/gems/ruby-1.9.3-p194@rails_3.2.8/gems/rake-0.9.2.2/lib/rake/task.rb:151:in `invoke_with_call_chain'
/Users/rogert/.rvm/gems/ruby-1.9.3-p194@rails_3.2.8/gems/rake-0.9.2.2/lib/rake/task.rb:144:in `invoke'
/Users/rogert/.rvm/gems/ruby-1.9.3-p194@rails_3.2.8/gems/activerecord-3.2.8/lib/active_record/railties/databases.rake:162:in `block (2 levels) in <top (required)>'
/Users/rogert/.rvm/gems/ruby-1.9.3-p194@rails_3.2.8/gems/rake-0.9.2.2/lib/rake/task.rb:205:in `call'
/Users/rogert/.rvm/gems/ruby-1.9.3-p194@rails_3.2.8/gems/rake-0.9.2.2/lib/rake/task.rb:205:in `block in execute'
/Users/rogert/.rvm/gems/ruby-1.9.3-p194@rails_3.2.8/gems/rake-0.9.2.2/lib/rake/task.rb:200:in `each'
/Users/rogert/.rvm/gems/ruby-1.9.3-p194@rails_3.2.8/gems/rake-0.9.2.2/lib/rake/task.rb:200:in `execute'
/Users/rogert/.rvm/gems/ruby-1.9.3-p194@rails_3.2.8/gems/rake-0.9.2.2/lib/rake/task.rb:158:in `block in invoke_with_call_chain'
/Users/rogert/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/monitor.rb:211:in `mon_synchronize'
$sudo vi /usr/local/var/postgres9.2/postgresql.conf
[search for listen address]
# - Connection Settings -
listen_addresses = 'localhost' # what IP address(es) to listen on;
# comma-separated list of addresses;
# defaults to 'localhost'; use '*' for all
# (change requires restart)
port = 5432 # (change requires restart)
max_connections = 100 # (change requires restart)
奇怪的是，如果我从rails应用程序中完全删除这两行，则迁移会起作用。因此，如果TCP连接存在问题并且存在，那么迁移本身是如何工作的（但是一旦我再次将这两个重新打开就不会这样）
答案 0 :(得分：5)
很可能你的PostgreSQL实例配置为不侦听TCP / IP，至少在localhost上。
在postgresql.conf检查listen_addresses。见the documentation。最有可能将其设置为''（空字符串），因此服务器仅侦听UNIX域套接字。
psql，pg_dump等仍然有效，因为它们默认连接到本地unix域套接字。 Ruby pg gem是libpq的包装器，psql等使用的相同客户端库，除非显式指定连接参数，否则它还默认使用unix域套接字。
但是，Rails似乎正在将显式IP地址传递给pg_dump - 导致它尝试通过TCP / IP进行连接，而Pg没有监听它，导致观察到“连接被拒绝”错误
或者，您的PostgreSQL可能默认编译为5432以外的端口。相同的设置在libpq中作为默认编译，因此它将自动连接到新端口。但是，如果Rails在尝试运行它时指定了pg_dump的显式端口，它将优先使用内置默认值。检查port中的postgresql.conf指令;如果未已注释掉或设置为5432，这可能是您的问题。 port指令记录在与上面链接的同一页面中。
顺便说一句，在Pg正在运行时找到postgresql.conf运行psql template1 -c "SHOW config_file;"。
答案 1 :(得分：1)
根本原因结果是第三方防火墙软件包认为过滤本地环回接口上的连接是一个好主意。
答案 2 :(得分：0)
pg_dump将使用UNIX域套接字访问PostgreSQL，而rails工具正在尝试创建到localhost的TCP连接。
看看你的pg_hba.conf（对我来说这是在/ var / lib / pgsql / data /中）并检查是否有这样的行，其中md5表示将使用密码验证：
host all all 127.0.0.1/32 md5
（如果要在生产环境中运行它，请确保完全理解这一点！）
通过在运行pg_dump时在命令行上显式指定-h localhost，可以测试通过TCP连接。如果对pg_hba.conf进行任何更改，请记得重新启动PostgreSQL。