Which one(s) have been recently updated and are suspect? Would they really have overwritten previously-configured options, or blithely added new ones which were enabled by default?
Previously, bind has started with bufsize=4096 and reduced it if the queried server says it can only provide smaller packets.
My understand is that the new behaviour is that it will start with bufsize=512 and raise it.
But what we are seeing is that some servers are failing to do this and so making excessive use of TCP.
Although I can't directly this effect with a code change - the timing is right and its the same area of the code.
And its been a very sudden change (we can identify the day it started happening) - which suggests code change, as opposed to a config change (i.e. it happened in a number of places at about the same time).
I said before, the fact remains that servers that are clearly capable of a larger bufsize but are sticking with a minimum sized one, and so re-issuing *ALL* their queries over UDP, then immediately again over TCP (where the target zone is signed).
At a minimum this doubles the workload on the target server, without taking into account the much higher workload of TCP over UDP.
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