AMB_RECEIVE semaphores hitting queue depth limit

[Tom Brown]

We have an external site that pulls KB data from our ServiceNow instance using table APIs.  We're seeing some intermittent errors where the connection is terminated.  While there are other potential areas of questionable behavior, one suspicion is that we might be exhausting the available semaphores.  Looking at the Default settings, we're only hitting a max of 14 of 150.  Under API_INT, it indicates that our max depth reached was 18 of the 50 available.  However, AMB_RECEIVE shows that it hit the max of 50 of the 50 allowed in the queue.  I haven't been able to find a definitive guide that tells what the various semaphores do, but I would have thought that the API_INT would have been the one to max out with API calls.    Thanks for any clarification on how these work.  I'm also curious how often those Max Queue Depth numbers reset.  If max queue depth was reached a month ago, it doesn't really help me today.

Semaphore details below:

Semaphore Sets

 
Default
Available semaphores: 16
Queue depth: 0
Queue age: 0:00:00.000
Max queue depth: 14
Queue depth limit: 150
Maximum transaction concurrency: 16
Maximum concurrency achieved: 8
 
Debug
Available semaphores: 4
Queue depth: 0
Queue age: 0:00:00.000
Max queue depth: 0
Queue depth limit: 50
Maximum transaction concurrency: 4
Maximum concurrency achieved: 0
 
AMB_RECEIVE
Available semaphores: 4
Queue depth: 0
Queue age: 0:00:00.000
Max queue depth: 50
Queue depth limit: 50
Maximum transaction concurrency: 4
Maximum concurrency achieved: 4
 
AMB_SEND
Available semaphores: 4
Queue depth: 0
Queue age: 0:00:00.000
Max queue depth: 10
Queue depth limit: 50
Maximum transaction concurrency: 4
Maximum concurrency achieved: 3
 
API_INT
Available semaphores: 4
Queue depth: 0
Queue age: 0:00:00.000
Max queue depth: 18
Queue depth limit: 50
Maximum transaction concurrency: 4
Maximum concurrency achieved: 4
 
Presence
Available semaphores: 8
Queue depth: 0
Queue age: 0:00:00.000
Max queue depth: 4
Queue depth limit: 50
Maximum transaction concurrency: 8
Maximum concurrency achieved: 7

[Ankur Bawiskar]

Hi Brown,

here is the link which should help you

https://community.servicenow.com/community?id=community_question&sys_id=b8b20defdb1fbf005129a851ca96...

Mark Correct if this solves your issue and also mark Helpful if you find my response worthy based on the impact.
Thanks
Ankur

[Tom Brown]

Thanks for the response.  I'm afraid that I didn't find what I needed on those links.  One takes me to an article that apparently I'm not allowed to see (KB0594813).  From the references, it may be involving the Geneva version.  It is interesting to see that the service should be responding with an http status code of 429, and I haven't seen that in the error messages being posted by the outside web page.  If you do find information about which semaphores are used for what purposes, I would appreciate it.