PG::UnableToSend: no connection to the server in Rails - ruby-on-rails

Question

I have a production server running ubuntu 14.04, Rails 4.2.0, postgresql 9.6.1 with gem pg 0.21.0/0.20.0. In last few days, there is constantly error with accessing to a table customer_input_datax_records in psql server.
D, [2017-07-20T18:08:39.166897 #1244] DEBUG -- : CustomerInputDatax::Record Load (0.1ms) SELECT "customer_input_datax_records".* FROM "customer_input_datax_records" WHERE ("customer_input_datax_records"."status" != $1) [["status", "email_sent"]]
E, [2017-07-20T18:08:39.166990 #1244] ERROR -- : PG::UnableToSend: no connection to the server
: SELECT "customer_input_datax_records".* FROM "customer_input_datax_records" WHERE ("customer_input_datax_records"."status" != $1)
The code which call to access the db server is with Rufus scheduler 3.4.2 loop:
s = Rufus::Scheduler.singleton
s.every '2m' do
new_signups = CustomerInputDatax::Record.where.not(:status => 'email_sent').all
.......
end
After restart the server, usually there is with first request (or a few). But after some time (ex, 1 or 2 hours), the issue starts to show up. But the app seems running fine (accessing records with read/write & creating new). There are some online posts about the error. However the problem seems not the one I am having. Before I re-install the psql server, I would like to get some ideas about what causes the no connection.
UPDATE: database.yml
production:
adapter: postgresql
encoding: unicode
host: localhost
database: wb_production
pool: 5
username: postgres
password: xxxxxxx

Answer 1

So, the error is "RAILS: PG::UnableToSend: no connection to the server".
That reminds me of Connection pool issue with ActiveRecord objects in rufus-scheduler
You could do
s = Rufus::Scheduler.singleton
s.every '2m' do
ActiveRecord::Base.connection_pool.with_connection do
new_signups = CustomerInputDatax::Record
.where.not(status: 'email_sent')
.all
# ...
end
end
digging
It would be great to know more about the problem.
I'd suggest trying this code:
s = Rufus::Scheduler.singleton
def s.on_error(job, error)
Rails.logger.error(
"err#{error.object_id} rufus-scheduler intercepted #{error.inspect}" +
" in job #{job.inspect}")
error.backtrace.each_with_index do |line, i|
Rails.logger.error(
"err#{error.object_id} #{i}: #{line}")
end
end
s.every '2m' do
new_signups = CustomerInputDatax::Record.where.not(:status => 'email_sent').all
# .......
end
As soon as the problem manifests itself, I'd look for the on_error full output in the Rails log.
This on_error comes from https://github.com/jmettraux/rufus-scheduler#rufusscheduleron_errorjob-error

Answer 2

As we discuss in the comments, the problem seems related to your rufus version.
I would suggest you to check out whenever gem and to invoke a rake task instead of calling directly the activerecord model.
It could be a good idea, however, to open an issue with the traceback of your error in the rufus-scheduler repo on github (just to let then know...)