Sidekiq Pro, Redis::CommandError: ERR wrong number of arguments for 'brpop' command, when pausing queue

[thibaudgg]

Ruby version: 2.6.6
Rails version: 6.0.3.5
Sidekiq / Pro / Enterprise version(s): 6.1.2 / 5.2.0 / 2.1.2

Hi,

We are getting this Redis::CommandError: ERR wrong number of arguments for 'brpop' command error, when pausing a queue from the Web UI queues list.

This issue is easily reproducible and is only happening when the paused queue is the only one processed by the sidekiq command, i.e. sidekiq-q default. When two queues are processed (i.e.sidekiq -q default -q low) this error isn't triggered unless the two queues are paused together. To resume, this is triggered when the last active queue is paused.

We found that this issue is coming from the basic_fetch strategy overwritten in Sidekiq Pro as we aren't using the super_fetch strategy.
Sidekiq Pro overwrittes the Sidekiq::Pro::BasicFetch::queues_cmd method and left the @queues variable empty when only one queue is processed (see queues = (@original - @paused.to_a).map { |q| "queue:#{q}" }), which then triggers this error from here: https://github.com/mperham/sidekiq/blob/3b5ae30c4e5e9e760268243ab5c14664a2f8d236/lib/sidekiq/fetch.rb#L39

Backtrace:

Redis::CommandError: ERR wrong number of arguments for 'brpop' command
 [GEM_ROOT]/gems/redis-4.2.2/lib/redis/client.rb:127 :in `call`
 [GEM_ROOT]/gems/redis-4.2.2/lib/redis/client.rb:221 :in `block in call_with_timeout`
 [GEM_ROOT]/gems/redis-4.2.2/lib/redis/client.rb:295 :in `with_socket_timeout`
 [GEM_ROOT]/gems/redis-4.2.2/lib/redis/client.rb:220 :in `call_with_timeout`
218	
219	    def call_with_timeout(command, timeout, &blk)
220	      with_socket_timeout(timeout) do
221	        call(command, &blk)
222	      end
 [GEM_ROOT]/gems/redis-4.2.2/lib/redis.rb:1224 :in `block in _bpop`
 [GEM_ROOT]/gems/redis-4.2.2/lib/redis.rb:69 :in `block in synchronize`
[PROJECT_ROOT]/vendor/ruby-2.6.6/lib/ruby/2.6.0/monitor.rb:235 :in `mon_synchronize`
 [GEM_ROOT]/gems/redis-4.2.2/lib/redis.rb:69 :in `synchronize`
 [GEM_ROOT]/gems/redis-4.2.2/lib/redis.rb:1221 :in `_bpop`
 [GEM_ROOT]/gems/redis-4.2.2/lib/redis.rb:1266 :in `brpop`
 [GEM_ROOT]/gems/sidekiq-6.1.2/lib/sidekiq/fetch.rb:39 :in `block in retrieve_work`
 [GEM_ROOT]/gems/sidekiq-6.1.2/lib/sidekiq.rb:98 :in `block in redis`
 [GEM_ROOT]/gems/connection_pool-2.2.3/lib/connection_pool.rb:63 :in `block (2 levels) in with`
 [GEM_ROOT]/gems/connection_pool-2.2.3/lib/connection_pool.rb:62 :in `handle_interrupt`
 [GEM_ROOT]/gems/connection_pool-2.2.3/lib/connection_pool.rb:62 :in `block in with`
 [GEM_ROOT]/gems/connection_pool-2.2.3/lib/connection_pool.rb:59 :in `handle_interrupt`
 [GEM_ROOT]/gems/connection_pool-2.2.3/lib/connection_pool.rb:59 :in `with`
 [GEM_ROOT]/gems/sidekiq-6.1.2/lib/sidekiq.rb:95 :in `redis`
 [GEM_ROOT]/gems/sidekiq-6.1.2/lib/sidekiq/fetch.rb:39 :in `retrieve_work`
 [GEM_ROOT]/gems/sidekiq-6.1.2/lib/sidekiq/processor.rb:83 :in `get_one`
 [GEM_ROOT]/gems/sidekiq-6.1.2/lib/sidekiq/processor.rb:95 :in `fetch`
 [GEM_ROOT]/gems/sidekiq-6.1.2/lib/sidekiq/processor.rb:77 :in `process_one`
 [GEM_ROOT]/gems/sidekiq-6.1.2/lib/sidekiq/processor.rb:68 :in `run`
 [GEM_ROOT]/gems/sidekiq-6.1.2/lib/sidekiq/util.rb:15 :in `watchdog`
 [GEM_ROOT]/gems/sidekiq-6.1.2/lib/sidekiq/util.rb:24 :in `block in safe_thread`

[thibaudgg]

Thanks for the quick fix @mperham! 👍