varnish Monitoring Varnish Monitoring threads

Help us to keep this website almost Ad Free! It takes only 10 seconds of your time:
> Step 1: Go view our video on YouTube: EF Core Bulk Extensions
> Step 2: And Like the video. BONUS: You can also share it!


You need to keep track of some threads metrics to watch your Varnish Cache. Is it running out of OS resources or is it functioning well.

  • threads - Number of threads in all pools.
  • threads_created - Number of created threads.
  • threads_failed - Number of times Varnish failed to create a thread.
  • threads_limited - Number of times Varnish was forced not to create a thread since it was maxed out.
  • thread_queue_len - Current queue length. Number of requests waiting for a thread.
  • sess_queued - Number of times there wasn't any threads available so a request had to be queued.
varnishstat -1 | grep "threads\|thread_queue_len\|sess_queued"
MAIN.threads                     100          .   Total number of threads
MAIN.threads_limited               1         0.00 Threads hit max
MAIN.threads_created            3715         0.00 Threads created
MAIN.threads_destroyed          3615         0.00 Threads destroyed
MAIN.threads_failed                0         0.00 Thread creation failed
MAIN.thread_queue_len              0          .   Length of session queue
MAIN.sess_queued                2505         0.00 Sessions queued for thread

If thread_queue_len isn't 0 it means that Varnish is out of resources and have started to queue requests. This will decrease performance of those requests. You need to investigate why.

Watch also out for threads_failed. If this increases it means your server is out of resources somehow. Increasing numbers in threads_limited means you might need to increase your servers thread_pool_max.

Got any varnish Question?