Difference between query hung and timeout

[J Doe]

Hi list,

I run a BIND 9.18.27 resolver on a small mail server.

Sometimes in the logs I will see entries similar to the following:

     04-Jul-2024 12:20:48.048 query-errors: info: client @0x3777f6412b0
         127.0.0.1#48123 (bras-base-toroon0964w-
         grc-41-142-198-14-9.dsl.bell.ca): query failed (timed out) for
         bras-base-toroon0964w-grc-41-142-198-14-9.dsl.bell.ca/IN/A at
         query.c:7843

     04-Jul-2024 20:07:35.308 resolver: info: shut down hung fetch
         while resolving '164.212.87.77.in-addr.arpa/PTR'

My question is: what is the difference between a query that times out
versus a query that hangs ?

In both cases, I would think these queries are hitting a time limit and
are stopped by BIND, but  the fact that there are two different log
entries makes me wonder if there's more to this.

Thanks,

- J