How to manage opening and closing database connections while working with activerecords and multiple threads

Question

I am trying to implement a multithreaded method in rails such that I can create/update multiple records very quickly.

This is the outline of my program.

Answer 1

To prevent connection leak in multi threads, you have to manage the connection manually. You can try:

Thread.new do
  ActiveRecord::Base.connection_pool.with_connection do
    # Do whatever
  end
end

One problem of ActiveRecord::Base.connection_pool.with_connection is that it always prepare a connection even if the code inside does not need it.

We can improve it a little bit by using ActiveRecord::Base.connection_pool.release_connection:

Thread.new do
  begin
    # Do whatever
  ensure
    ActiveRecord::Base.connection_pool.release_connection
  end
end

Answer 2

if you want to run in N threads, make sure you have N connections in the pool

#  ActiveRecord::Base.connection_config
#  # => {pool: 5, timeout: 5000, database: "db/development.sqlite3", adapter: "sqlite3"}

otherwise you will be able to fetch a connection from the pool.