If one of the mongods in your replica set starts
> refusing connections (because, say, you have a process that is leaking
> fds and has a ton of open connections to it), then you get the
> following error while trying to talk to a set containing it (even if
> it's not your primary).
>
> NoMethodError: undefined method `primary_pool' for nil:NilClass
> from /usr/lib/ruby/gems/1.8/gems/mongo-1.5.1/lib/../lib/mongo/repl_set_connection.rb:388:in
> `primary_pool'
> from /usr/lib/ruby/gems/1.8/gems/mongo-1.5.1/lib/../lib/mongo/repl_set_connection.rb:344:in
> `checkin_writer'
> from /usr/lib/ruby/gems/1.8/gems/mongo-1.5.1/lib/../lib/mongo/cursor.rb:574:in
> `force_checkin_socket'
> from /usr/lib/ruby/gems/1.8/gems/mongo-1.5.1/lib/../lib/mongo/cursor.rb:474:in
> `send_initial_query'
> from /usr/lib/ruby/gems/1.8/gems/mongo-1.5.1/lib/../lib/mongo/util/logging.rb:28:in
> `instrument'
> from /usr/lib/ruby/gems/1.8/gems/mongo-1.5.1/lib/../lib/mongo/cursor.rb:468:in
> `send_initial_query'
> from /usr/lib/ruby/gems/1.8/gems/mongo-1.5.1/lib/../lib/mongo/cursor.rb:458:in
> `refresh'
> from /usr/lib/ruby/gems/1.8/gems/mongo-1.5.1/lib/../lib/mongo/cursor.rb:128:in
> `next_document'
> from /usr/lib/ruby/gems/1.8/gems/mongo-1.5.1/lib/../lib/mongo/db.rb:505:in
> `command'
> from /usr/lib/ruby/gems/1.8/gems/mongo-1.5.1/lib/../lib/mongo/util/node.rb:87:in
> `set_config'
> from /usr/lib/ruby/gems/1.8/gems/mongo-1.5.1/lib/../lib/mongo/util/pool_manager.rb:149:in
> `connect_to_members'
> from /usr/lib/ruby/gems/1.8/gems/mongo-1.5.1/lib/../lib/mongo/util/pool_manager.rb:147:in
> `each'
> from /usr/lib/ruby/gems/1.8/gems/mongo-1.5.1/lib/../lib/mongo/util/pool_manager.rb:147:in
> `connect_to_members'
> from /usr/lib/ruby/gems/1.8/gems/mongo-1.5.1/lib/../lib/mongo/util/pool_manager.rb:25:in
> `connect'
> from /usr/lib/ruby/gems/1.8/gems/mongo-1.5.1/lib/../lib/mongo/repl_set_connection.rb:156:in
> `connect'
> from /usr/lib/ruby/gems/1.8/gems/mongo-1.5.1/lib/../lib/mongo/repl_set_connection.rb:468:in
> `setup'
> from /usr/lib/ruby/gems/1.8/gems/mongo-1.5.1/lib/../lib/mongo/repl_set_connection.rb:143:in
> `initialize'
> from (irb):9:in `new'
> from (irb):9
>