如何使用ActiveRecord Rails 5打开和关闭新的数据库连接

Question

I have some workloads that need to increase WORK_MEM and TEMP_BUFFERS . The problem is, once I do this, the connection (session) is not closed and is returned to the pool. This means the extra memory usage isn't temporary because I can't change TEMP_BUFFERS back without destroying the session.

I imagine the workflow going something like this:

conn = ActiveRecord.create_new_connection
conn.execute <<-SQL
  SET TEMP_BUFFERS TO '512MB';
  -- do some memory intensive 
  CREATE TEMPORARY TABLE .....;
  UPDATE ....;
SQL
conn.close

Or maybe there is a way to close the current connection and have the pool crate a new one...

Answer 1

Seems like new_connection is a private method , which is what we need to manually create a connection outside being part of the pool,

Then, upon inspecting the source code, you can do something like this:

connection_specification = ActiveRecord::Base.connection_pool.spec
# i.e.
#   connection_specification.adapter_method == 'postgresql_connection'
#   connection_specification.config == {:adapter=>"postgresql", :encoding=>"unicode", :pool=>5, :database=>"someapp_development"}

connection = ActiveRecord::Base.send(
  connection_specification.adapter_method, 
  connection_specification.config
)

# DEBUG:
puts connection.active?
# => true

connection.execute <<-SQL
  SET TEMP_BUFFERS TO '512MB';
  -- do some memory intensive 
  CREATE TEMPORARY TABLE .....;
  UPDATE ....;
SQL

connection.disconnect!

# DEBUG:
puts connection.active?
# => false