Rails 5 db迁移：如何修复ActiveRecord :: ConcurrentMigrationError [英] Rails 5 db migration: how to fix ActiveRecord::ConcurrentMigrationError

问题描述

先前的rake db：rollback已停止。现在，当尝试进行新的迁移时，会出现以下错误：

A previous rake db:rollback stalled. Now when attempting a new migration we get the following error:

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)

使用Postresql

We are using Postresql

推荐答案

在Rails 5中添加了咨询锁定，以防止迁移期间发生计划外的并发错误。解决方法是清除保留的数据库锁。

Advisory locking was added in Rails 5 to prevent unplanned concurrency errors during migration. The fix is to clear the DB lock that was left in place.

通过对您的数据库运行此SQL来查看锁：

Review the locks by running this SQL against your DB:

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：

To clear a lock, run this SQL against your DB:

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

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