问题:Rails 5 db 迁移:如何修复 ActiveRecord::ConcurrentMigrationError

先前的 rake db:rollback 停止。现在,在尝试新迁移时,我们收到以下错误:

rake aborted!
ActiveRecord::ConcurrentMigrationError: 

Cannot run migrations because another migration process is currently running.

/home/me/.rvm/gems/ruby-2.4.1@global/gems/activerecord-    5.1.4/lib/active_record/migration.rb:1315:in `with_advisory_lock'
/home/me/.rvm/gems/ruby-2.4.1@global/gems/activerecord-5.1.4/lib/active_record/migration.rb:1148:in `migrate'
/home/me/.rvm/gems/ruby-2.4.1@global/gems/activerecord-5.1.4/lib/active_record/migration.rb:1007:in `up'
/home/me/.rvm/gems/ruby-2.4.1@global/gems/activerecord-5.1.4/lib/active_record/migration.rb:985:in `migrate'
/home/me/.rvm/gems/ruby-2.4.1@global/gems/activerecord-5.1.4/lib/active_record/tasks/database_tasks.rb:171:in `migrate'
/home/me/.rvm/gems/ruby-2.4.1@global/gems/activerecord-5.1.4/lib/active_record/railties/databases.rake:58:in `block (2 levels) in <top (required)>'
/home/me/.rvm/gems/ruby-2.4.1/gems/rake-12.1.0/exe/rake:27:in `<top (required)>'
/home/me/.rvm/gems/ruby-2.4.1/bin/ruby_executable_hooks:15:in `eval'
/home/me/.rvm/gems/ruby-2.4.1/bin/ruby_executable_hooks:15:in `<main>'
Tasks: TOP => db:migrate
(See full trace by running task with --trace)

我们正在使用 Postgresql

解答

Rails 5 中添加了咨询锁定,以防止迁移期间出现计划外的并发错误。解决方法是清除留在原处的数据库锁。

通过对您的数据库运行此 SQL 来查看锁:

SELECT DISTINCT age(now(), query_start) AS age, pg_stat_activity.pid,pg_locks.granted,pg_stat_activity.application_name,pg_stat_activity.backend_start, pg_stat_activity.xact_start, pg_stat_activity.state_change, pg_stat_activity.waiting, pg_stat_activity.state, pg_stat_activity.query_start, left(pg_stat_activity.query, 60)
FROM pg_stat_activity, pg_locks
WHERE pg_locks.pid = pg_stat_activity.pid

要清除锁定,请对您的数据库运行此 SQL:

select pg_advisory_unlock({the pid of the lock you want to release})