踩坑 postgresql。
问题描述
执行rake db: migrate时，中断，再次执行rake db: migrate时，报错：
psql: could not connect to server: Connection refused
Is the server running on host "localhost" (::1) and accepting
TCP/IP connections on port 5432?
解决过程
重启posgresql：
brew services restart postgresql
显示：
Stopping `postgresql`... (might take a while)
==> Successfully stopped `postgresql` (label: homebrew.mxcl.postgresql)
==> Successfully started `postgresql` (label: homebrew.mxcl.postgresql)
再次运行：
rake db:migrate
报错：
psql: could not connect to server: Connection refused
Is the server running on host "localhost" (::1) and accepting
TCP/IP connections on port 5432?
改成手动启动：
postges -D /usr/local/var/postgres/
报错：
FATAL: pre-existing shared memory block (key 5432001, ID 65536) is still in use
HINT: If you're sure there are no old server processes still running, remove the shared memory block or just delete the file "postmaster.pid".
切换到/usr/local/var/postgres 下，删除postmaster.pid 文件，然后重启：
postgres -D /usr/local/var/postgres/
重启后，再次运行：
rake db:migrate
报错：
PG::ConnectionBad: FATAL: the database system is starting up
Google后，尝试修改了postgresql.conf文件，将hot_standby 设置为on，重启Postgresql，继续执行rake db:migrate, 依然报错：
PG::ConnectionBad: FATAL: the database system is starting up
最后的解决方法：
简单粗暴：删除文件夹 /usr/local/var/postgres，卸载并重装PostgreSQL，重新导入数据。