[joevandyk]

I figured that serializable transactions would be necessary. That's going to be the default?

If you forget to use serializable transactions every time you update these tables, is it possible to store incorrect data?

[jeffdavis]

I think that SERIALIZABLE should be the default eventually, but others may disagree and I won't make a prediction.

However, it isn't necessary to solve the problem. It would be relatively easy to use a row lock in this case to solve the problem, as well, but I like to avoid those unless there's a reason.

If you want to have a mix of SERIALIZABLE and other transactions, or you are worried about making a mistake (or some malicious user), then you need to use the row lock. Eventually there should be a way to force users into serializable transactions.

EDIT: actually, in the trigger, you could explicitly check if the transaction isolation mode is serializable. That would be the best approach:

  if current_setting('transaction_isolation') <> 'serializable' then
    raise exception 'serializable mode required';
  end if;