In Production :: could not obtain a database connection within 5.000 seconds (waited 5.000 seconds) (ActiveRecord::ConnectionTimeoutError)

I am getting the error

/home/yaswant/.rvm/gems/ruby-2.2.1/gems/activerecord-4.2.5/lib/active_record/connection_adapters/abstract/connection_pool.rb:189:in `block in wait_poll': could not obtain a database connection within 5.000 seconds (waited 5.000 seconds) (ActiveRecord::ConnectionTimeoutError)

my connection pool have 30 connection. my app is api based application where i am using threads out side the rails . Please suggest me Thanks in advance