在我的Rails App（v 3.2.8）中，到目前为止，我使用了毫无问题的迁移。
我将PostgreSQL 9.2用作DB。我对application.rb进行了调整以使用SQL代替SQL（无调的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)
===========
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)
很奇怪的是，如果我完全从铁轨应用程序中删除了这两条线，则迁移有效。因此，如果这是TCP连接和上述内容的问题，那么迁移本身如何工作（但我再次重新打开这两个迁移）
- 应用
- 在我的一个迁移文件中 - t.hstore：属性
很可能您的postgresql实例是不在tcp/ip上收听的，至少在localhost上。
在postgresql.conf中检查listen_addresses。请参阅文档。最有可能将其设置为''（空字符串），因此服务器仅在Unix域插座上听。
psql，pg_dump等如果PG不在TCP/IP上收听，因为它们默认连接到本地Unix域套接字。Ruby pg GEM是围绕libpq的包装器，psql等使用的同一客户端库，除非明确指定连接参数，否则它默认使用UNIX域套接字。
但是，Rails似乎正在将明确的IP地址传递给pg_dump-导致其尝试通过TCP/IP连接，看来PG没有侦听，从而导致观察到的"连接拒绝"错误。
另外，您的PostgreSQL可能会编译为默认为5432以外的端口。相同的设置在LIBPQ中的默认设置中被编译为默认设置，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的明确端口，则它将优先使用该端口，而不是内置默认值。检查postgresql.conf中的port指令;如果不是注释或设置为5432，这可能是您的问题。port指令记录在链接到上面的同一页面中。
btw，要在PG运行时找到postgresql.conf运行psql template1 -c "SHOW config_file;"。
根本原因是第三方防火墙软件包，认为在本地环回接口上过滤连接是一个好主意。
请参阅评论线程。
pg_dump从命令行中使用Unix-domain套接字访问PostgreSQL，而Rails工具正在尝试创建与LocalHost的TCP连接。
请查看您的pg_hba.conf（对我来说，这是/var/lib/pgsql/data/），并检查是否有这样的行，其中md5表示使用密码身份验证：
host all all 127.0.0.1/32 md5
（如果要在生产环境中运行它，请确保您完全理解这一点！）
您可以通过在运行pg_dump时在命令行上明确指定-h localhost来通过TCP进行测试。如果您对pg_hba.conf进行任何更改，请记住重新启动PostgreSQL。