Rails 5 db migration：如何修复ActiveRecord :: ConcurrentMigrationError

Question

之前的rake db：rollback停滞不前。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

Answer 1

在Rails 5中添加了建议锁定，以防止在迁移期间出现意外的并发错误。修复方法是清除留在原位的DB锁。

通过针对您的数据库运行此SQL来检查锁：

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，请对数据库运行此SQL：

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

Answer 2

所以在我的情况下，查询是不同的

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.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

这基本上会告诉你pids

0 years 0 mons 0 days 0 hours 0 mins -0.01005 secs    360    true    PostgreSQL JDBC Driver    2019-04-03 16:57:16.873609    2019-04-03 16:58:00.531675    2019-04-03 16:58:00.541727    active    2019-04-03 16:58:00.541725    SELECT DISTINCT age(now(), query_start) AS age, pg_stat_acti
    17272    true    ""                        <insufficient privilege>
    22640    true    ""                        <insufficient privilege>
    29466    true    ""                        <insufficient privilege>

之后你可以用以下命令解锁pid：select pg_advisory_unlock(#{target_pid})

e.f.:

select pg_advisory_unlock(17272)
select pg_advisory_unlock(22640)
select pg_advisory_unlock(22640)
select pg_advisory_unlock(360)

干杯!

Answer 3

如果您正在使用数据库中的数据进行操作，而不是表格和列设置，那么一次rake任务可能是更好的地方吗？