暂时增加 Rails 中 Postgres 查询的“statement_timeout”？

Question

我已经将database.yml 中的statement_timeout 配置为几秒钟，但我的应用程序中有一些昂贵的查询，这需要更长的查询执行时间。在每个查询级别上实现此目标的推荐方法是什么？ 我需要临时将statement_timeout 设置为更大的值，执行查询并将其重置为默认值？或者甚至不需要重置？

Answer 1

我认为您只能通过更改整个连接的statement_timeout 然后将其恢复回来来实现：

  def execute_expensive_query
    ActiveRecord::Base.connection.execute 'SET statement_timeout = 600000' # 10 minutes
    # DB query with long execution time
  ensure
    ActiveRecord::Base.connection.execute 'SET statement_timeout = 5000' # 5 seconds
  end

在数据库级别，您可以为当前事务设置statement_timeout，仅按照this guide：

BEGIN;
SET LOCAL statement_timeout = 250;
...
COMMIT;

Answer 2

为了扩展已接受的答案，以下是实现模块 DatabaseTimeout 的方法，该模块还确保将 statement_timeout 设置重置为其原始值。

# Ruby's `Timeout` doesn't prevent queries from running for a long time.
#
# To prove this, run the following in a console (yes, twice):
#   Timeout.timeout(1.second) { ActiveRecord::Base.connection.execute('SELECT pg_sleep(100);') }
#   Timeout.timeout(1.second) { ActiveRecord::Base.connection.execute('SELECT pg_sleep(100);') }
# => The 2nd call should run for a long time.
#
# DatabaseTimeout's purpose is to enforce that each query doesn't run for more than the given timeout:
#   DatabaseTimeout.timeout(1.second) { ActiveRecord::Base.connection.execute('SELECT pg_sleep(100);') }
#   DatabaseTimeout.timeout(1.second) { ActiveRecord::Base.connection.execute('SELECT pg_sleep(100);') }
# => Both queries are interrupted after 1 second
module DatabaseTimeout
  # Usage: DatabaseTimeout.timeout(10) { run_some_query }
  def self.timeout(nb_seconds)
    original_timeout = ActiveRecord::Base.connection.execute('SHOW statement_timeout').first['statement_timeout']
    ActiveRecord::Base.connection.execute("SET statement_timeout = '#{nb_seconds.to_i}s'")
    yield
  ensure
    if original_timeout
      ActiveRecord::Base.connection.execute("SET statement_timeout = #{original_timeout}")
    end
  end
end