Governor limit for concurrent long-running transactions

Question

In the Governor limits, there is the following limit:

Number of synchronous concurrent transactions for long-running transactions that last longer than 5 seconds for each org.

If i create a custom Apex REST resource (e.g. using @RestResource(urlMapping='/whatever/v1/*') annotation), and inside this resource in the actions i run some heavy SOQL queries, and i have a few thousand users call this API all at once (they do it via a mobile app in the field), and it so happens that some requests take longer than 5 seconds, are those considered long-running transactions?

Does it mean other users will be denied (what it says on the same page)?

Answer 1

Yes. The system will observe that there are too many requests over 5 seconds long and deny any further requests until the long-running ones complete. In that case, you'd need the client to retry.