We are using https://github.com/php-amqplib/php-amqplib to consume messages from a rabbitmq. We've got several consumers that are running happily with no issues. Today we discovered that one of our consumer processes is consuming around 7% CPU of the host when idling (no messages in the queue) whereas the rest are consuming about 1% each.
On top of that when switching this process on and off we see large changes in the CPU utilizations of our db (AWS RDS postgres instance). With 3 consumer processes running our DB is at >30% CPU utilization all the time (even when there's nothing in the queue).
We've got a standard symfony configuration and our consumers are run using app/console rabbitmq:consumer -w consumer_name. The consumer in question has nothing special about it as far as we can tell. We are completely out of clues here so any help will be much appreciated.
more details:
When we turn the on the consumer we can see the same set of queries running a huge amount of times on the db (200,001 times in the space of 10minutes). There are no unacked messages in the queue. The consumer processes messages correctly otherwise. The query is a SELECT that would be run normally as part of the logic of the consumer.