>> IMO in read_commited wait reasonable person will make
>>only incremental updates like Set a=a+b,
>Wrong. Person should be able to do whatever at this isolation level.

From my university DBMS course I have a vague
recollection of something called "incremental locking" --
a special kind of transaction which specifically _allows_
unordered changes to the record, but requires them to be
of the "incremental" kind, like SET A=A+B.
I believe it is described in "Database Systems" by Ullman
& Widom. Unfortunately, my copy is in Russian ;)
Not at all sure if such method is worth implementing, but
it seems to fit at least this concrete case perfectly.
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