There are in fact two-and-half different kinds of deadlocks.

* One is not deadlock at all, but ordinary "update conflict"
(unfortunately the message you get for no wait transaction
say that it is deadlock)

* Another is real deadlock, caused by two (or more) transactions
that update data in some "unfortunate" order.
Firebird will detect such situation and kill one of the statements
that were waiting.
Nothing is written in firebird.log.

* The last one (which is what this thread is about) is internal
deadlock in mechanism for handling data pages (as described by Ann).
This one is the deadlock logged in "firebird.log".

Ivan