AlreadyHave is called for transactions in 3 places:
- when an INV is received to decide whether to schedule a request of the tx
- when a TX is received to decide whether to process it
- when actually requesting a tx to see if it has been received since scheduling the request
In a large number of these cases, the transaction in question is new and fails each of the tests in the return statement. In particular it is very unlikely (< 10%) to hit the pcoinsTip check and then be found. But pcoinsTip must check the database to be sure it can't find the transaction. Switching the full HaveCoins check for the fast HaveCoinsInCache check will still prevent the vast majority of false negatives but will never need a database access. The downside is after the cache has been flushed there maybe be a very few more cases of requesting already confirmed transactions from peers.
