Rails + Postgres 删除错误: 其他用户正在访问数据库

Let your application close the connection when it's done. PostgreSQL doesn't keep connections open , it's the application keeping the connection.

Rails is likely connecting to the database to drop it but when you log in via phppgadmin it is logging in via the template1 or postgres database, thus you are not affected by it.

If you kill the running postgresql connections for your application, you can then run db:drop just fine. So how to kill those connections? I use the following rake task:

# lib/tasks/kill_postgres_connections.rake
task :kill_postgres_connections => :environment do
db_name = "#{File.basename(Rails.root)}_#{Rails.env}"
sh = <<EOF
ps xa \
| grep postgres: \
| grep #{db_name} \
| grep -v grep \
| awk '{print $1}' \
| xargs kill
EOF
puts `#{sh}`
end


task "db:drop" => :kill_postgres_connections

Killing the connections out from under rails will sometimes cause it to barf the next time you try to load a page, but reloading it again re-establishes the connection.

Here's a quick way to kill all the connections to your postgres database.

sudo kill -9 `ps -u postgres -o pid`

Warning: this will kill any running processes that the postgres user has open, so make sure you want to do this first.

When we used the "kill processes" method from above, the db:drop was failing (if :kill_postgres_connections was prerequisite). I believe it was because the connection which that rake command was using was being killed. Instead, we are using a sql command to drop the connection. This works as a prerequisite for db:drop, avoids the risk of killing processes via a rather complex command, and it should work on any OS (gentoo required different syntax for kill).

cmd = %(psql -c "SELECT pg_terminate_backend(procpid) FROM pg_stat_activity WHERE procpid <> pg_backend_pid();" -d '#{db_name}')

Here is a rake task that reads the database name from database.yml and runs an improved (IMHO) command. It also adds db:kill_postgres_connections as a prerequisite to db:drop. It includes a warning that yells after you upgrade rails, indicating that this patch may no longer be needed.

see: https://gist.github.com/4455341, references included

I use the following rake task to override the Rails drop_database method.

lib/database.rake

require 'active_record/connection_adapters/postgresql_adapter'
module ActiveRecord
module ConnectionAdapters
class PostgreSQLAdapter < AbstractAdapter
def drop_database(name)
raise "Nah, I won't drop the production database" if Rails.env.production?
execute <<-SQL
UPDATE pg_catalog.pg_database
SET datallowconn=false WHERE datname='#{name}'
SQL


execute <<-SQL
SELECT pg_terminate_backend(pg_stat_activity.pid)
FROM pg_stat_activity
WHERE pg_stat_activity.datname = '#{name}';
SQL
execute "DROP DATABASE IF EXISTS #{quote_table_name(name)}"
end
end
end
end

You can simply monkeypatch the ActiveRecord code that does the dropping.

For Rails 3.x:

# lib/tasks/databases.rake
def drop_database(config)
raise 'Only for Postgres...' unless config['adapter'] == 'postgresql'
Rake::Task['environment'].invoke
ActiveRecord::Base.connection.select_all "select pg_terminate_backend(pg_stat_activity.pid) from pg_stat_activity where datname='#{config['database']}' AND state='idle';"
ActiveRecord::Base.establish_connection config.merge('database' => 'postgres', 'schema_search_path' => 'public')
ActiveRecord::Base.connection.drop_database config['database']
end

For Rails 4.x:

# config/initializers/postgresql_database_tasks.rb
module ActiveRecord
module Tasks
class PostgreSQLDatabaseTasks
def drop
establish_master_connection
connection.select_all "select pg_terminate_backend(pg_stat_activity.pid) from pg_stat_activity where datname='#{configuration['database']}' AND state='idle';"
connection.drop_database configuration['database']
end
end
end
end

(from: http://www.krautcomputing.com/blog/2014/01/10/how-to-drop-your-postgres-database-with-rails-4/)

Just make sure that the you have exited the rails console on any open terminal window and exited the rails server...this is one of the most common mistake made by people

I had a similar error saying 1 user was using the database, I realized it was ME! I shut down my rails server and then did the rake:drop command and it worked!

Please check if your rails console or server is running in another tab and then

stop the rails server and console.

then run

 rake db:drop

I wrote a gem called pgreset that will automatically kill connections to the database in question when you run rake db:drop (or db:reset, etc). All you have to do is add it to your Gemfile and this issue should go away. At the time of this writing it works with Rails 4 and up and has been tested on Postgres 9.x. Source code is available on github for anyone interested.

gem 'pgreset'

Easier and more updated way is: 1. Use ps -ef | grep postgres to find the connection # 2. sudo kill -9 "# of the connection

Note: There may be identical PID. Killing one kills all.

After restarting the server or computer, please try again.

It could be the simple solution.

Solution

Bash script

ENV=development


# restart postgresql
brew services restart postgresql


# get name of the db from rails app
RAILS_CONSOLE_COMMAND="bundle exec rails c -e $ENV"
DB_NAME=$(echo 'ActiveRecord::Base.connection_config[:database]' | $RAILS_CONSOLE_COMMAND | tail -2 | tr -d '\"')


# delete all connections to $DB_NAME
for pid in $(ps -ef | grep $DB_NAME | awk {'print$2'})
do
kill -9 $pid
done


# drop db
DISABLE_DATABASE_ENVIRONMENT_CHECK=1 RAILS_ENV=$ENV bundle exec rails db:drop:_unsafe

I had this same issue when working with a Rails 5.2 application and PostgreSQL database in production.

Here's how I solved it:

First, log out every connection to the database server on the PGAdmin Client if any.

Stop every session using the database from the terminal.

sudo kill -9 `ps -u postgres -o pid=`

Start the PostgreSQL server, since the kill operation above stopped the PostgreSQL server.

sudo systemctl start postgresql

Drop the database in the production environment appending the production arguments.

rails db:drop RAILS_ENV=production DISABLE_DATABASE_ENVIRONMENT_CHECK=1

That's all.

I hope this helps

This worked for me (rails 6): rake db:drop:_unsafe

I think we had something in our codebase that initiated a db connection before the rake task attempted to drop it.

Step 1

Get a list of all postgres connections with ps -ef | grep postgres

The list will look like this:

  502   560   553   0 Thu08am ??         0:00.69 postgres: checkpointer process
502   565   553   0 Thu08am ??         0:00.06 postgres: bgworker: logical replication launcher
502 45605   553   0  2:23am ??         0:00.01 postgres: st myapp_development [local] idle

Step 2

Stop whatever connection you want with sudo kill -9 <pid>, where pid is the value in the second column. In my case, I wanted to stop the last row, with pid 45605, so I use:

sudo kill -9 45605

[OSX][Development/Test] Sometimes it is hard to determine the proper PID when you have a lot of PostgreSQL processes like checkpointer, autovacuum launcher, etc. In this case, you can simply run:

brew services restart postgresql@12

If you dockerized your app, then restart your db service

sudo docker-compose restart db

ActiveRecord::StatementInvalid: PG::ObjectInUse: ERROR: database "database_enviroment" is being accessed by other users DETAIL: There is 1 other session using the database.

For rails 7: you can use -> rails db:purge