Mysql2::Error:关闭MySQL连接

Question

运行：

Timeout.timeout(1) { User.find_by_sql('SELECT sleep(2) FROM users;') }

返回以下内容：

  User Load (1004.2ms)  SELECT sleep(2) FROM users;
ActiveRecord::StatementInvalid: : execution expired: SELECT sleep(2) FROM users;
    from /Users/Chris/.rvm/gems/ruby-1.9.2-p290/gems/activerecord-3.1.3/lib/active_record/connection_adapters/mysql2_adapter.rb:687:in `query'
    from /Users/Chris/.rvm/gems/ruby-1.9.2-p290/gems/activerecord-3.1.3/lib/active_record/connection_adapters/mysql2_adapter.rb:687:in `block in exec_query'
    from /Users/Chris/.rvm/gems/ruby-1.9.2-p290/gems/activerecord-3.1.3/lib/active_record/connection_adapters/abstract_adapter.rb:244:in `block in log'
    from /Users/Chris/.rvm/gems/ruby-1.9.2-p290/gems/activesupport-3.1.3/lib/active_support/notifications/instrumenter.rb:21:in `instrument'
    from /Users/Chris/.rvm/gems/ruby-1.9.2-p290/gems/activerecord-3.1.3/lib/active_record/connection_adapters/abstract_adapter.rb:239:in `log'
    from /Users/Chris/.rvm/gems/ruby-1.9.2-p290/gems/activerecord-3.1.3/lib/active_record/connection_adapters/mysql2_adapter.rb:685:in `exec_query'
    from /Users/Chris/.rvm/gems/ruby-1.9.2-p290/gems/activerecord-3.1.3/lib/active_record/connection_adapters/mysql2_adapter.rb:679:in `select'
    from /Users/Chris/.rvm/gems/ruby-1.9.2-p290/gems/activerecord-3.1.3/lib/active_record/connection_adapters/abstract/database_statements.rb:18:in `select_all'
    from /Users/Chris/.rvm/gems/ruby-1.9.2-p290/gems/activerecord-3.1.3/lib/active_record/connection_adapters/abstract/query_cache.rb:63:in `select_all'
    from /Users/Chris/.rvm/gems/ruby-1.9.2-p290/gems/activerecord-3.1.3/lib/active_record/base.rb:470:in `find_by_sql'
    from (irb):1:in `block in irb_binding'
    from /Users/Chris/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/timeout.rb:58:in `timeout'
    from (irb):1
    from /Users/Chris/.rvm/gems/ruby-1.9.2-p290/gems/railties-3.1.3/lib/rails/commands/console.rb:45:in `start'
    from /Users/Chris/.rvm/gems/ruby-1.9.2-p290/gems/railties-3.1.3/lib/rails/commands/console.rb:8:in `start'
    from /Users/Chris/.rvm/gems/ruby-1.9.2-p290/gems/railties-3.1.3/lib/rails/commands.rb:40:in `<top (required)>'
    from script/rails:6:in `require'
    from script/rails:6:in `

对于PgSql，似乎不会发生以下情况。Mysql2或ActiveRecord中有没有bug？

我读到过，当mysql无法处理太多的连接时，就会发生这种情况。但是为什么这不会发生在PgSql上呢？

PS。我正在使用Amazon RDS，如果这有什么不同的话。

Answer 1

当然，您在Timeout.timeout(1)块中执行此操作，我认为您应该设置更长的超时。

Answer 2

它在MySql中给出错误而不是PgSql错误的原因是，睡眠是一个有效的Mysql函数，但不是一个有效的Pgsql函数。后者中的正确函数是pg_sleep。也就是说，查询休眠2秒，而在Ruby代码中，您将执行限制为1秒，因此会引发超时异常。对于Pg的情况，它应该给出另一种类型的异常，比如“睡眠不是一个有效的pgsql函数”。