How does clients-per-query work when named is running?
A client in this scenario is a unique query that has been received by named and which should receive its own query response. (Duplicate queries are identified and discarded)
named limits the number of clients that can simultaneously be querying for a particular name/type. The initial limit is "clients-per-query, which by default starts at 10. If 10 clients are already waiting for an answer for example.com/A, then the 11th client to ask for it is dropped. When an answer finally arrives for example.com/A, the limit is raised by 5.
Later, if there's another name/type that builds up to 15 clients waiting for an answer, and a 16th comes in and gets dropped, then when an answer arrives for that name, the limit will be raised to 20, and so on.
This continues until the limit has reached "max-clients-per-query", which defaults to 100.
After a while if named is getting along successfully with 100, it will try lowering the limit back down to 99, then 98, and so on until it reaches the original 10.
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