Overpass API developpement

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Hello,
In the transaction.log file
on the read_finished() start line there are lines such as:

yyyy-mm-dd hh:mm:ss [124716] read_finished() start 3915 14484 14484
yyyy-mm-dd hh:mm:ss [124716]  read_finished() start 78 278 226 52

1. What do the numbers 3915, 144484, 14484 mean?
2. Why sometimes 4 numbers and some times 3
3. Is it possible to estimate how long the query took from these numbers? Is
the query runtime related to these numbers?

4. Following the above type lines is:
yyyy-mm-dd hh:mm:ss [2092] waited idle for 12 cycles.
I assume 2092 is the main process. Is this 12 cycles a clue as to how long the
query took?

5. During the main process idle:  are incoming requests pending? [I don't know
if each query is handled serially]

Thank you