Understanding of Semaphores and Nodes

[Puru2]

Dear All,

While going through SNOW Docs, I came across Semaphores & Nodes. I further discovered that in order to set-up LDAP integration, some ports are needed. I wondered if these 3 quantities are inter-related as *Semaphore -> Nodes -> Ports* (decr. order) in order to set-up running environment within SNOW. Please let me know if my understanding is up to the mark , else needs some correction. Suggestions/Comments are welcome.

Best Regards,

Puru

[sergiu_panaite]

They are not related.

Nodes -> is a short name for "application nodes". A ServiceNow instance is made up of a couple of application nodes (Tomcat web servers) along with a database. When a user logs in, they end up on one of the available application nodes.

Semaphores -> this is a throttling concept and you can find plenty of information about it on the internet, like for example:

https://dzone.com/articles/java-concurrency-semaphores

Ports -> in case of LDAP integration, you will need to know the URL for the LDAP server (like an IP address) and a port of it (like 389 for LDAP and 636 for LDAPS).

Hope this helps.

Regards,
Sergiu

[mrbenwhite]

Thanks for the explanation this is real helpful.

[Tyler Teter]

I have a bit of an bone to pick with this definition, since I feel like it doesn't show the entire picture of how it really works in the context of ServiceNow and how they ARE RELATED.

ServiceNow defines Semaphores are: The average number of semaphores "in use" over a 1-minute period. In other words, the number of end user transactions being processed at once."
ServiceNow does not define "nodes" officially anywhere I have found, but we know that the running transactions are executed on nodes, and therefore by extension semaphores are running on nodes.

From my understanding, ServiceNow describes their nodes as containing contexts of semaphores, or a concurrent threads, where one has to be released so another can be used.

In this definition semaphores are more like the current executing transaction queue which each application node is processing.

In some places nodes and semaphores are used interchangeably, but that is not correct, albeit a small technical distinction. Semaphores exist as a logical construct on top of a physical/virtual node.