Can a low fee unconfirmed transaction prevent confirmations of following transactions? To be more precise, consider the following situation:


Address A gets an input of 4 BTC.
You try to make a transaction from A to B with 1 BTC and a very low fee, which means its unconfirmed for a long while. The transaction's output are B and A (to account for the change of ~3 BTC after fees)
Before waiting for the previous transaction to be confirmed, you send again from A to B, this time you send 2 BTC with a higher fee, hoping it'll be confirmed fast.


My question is, since the output of the first transaction is the same address A, will it need to be confirmed first for the second transaction to follow through, because the input of the second transaction is A?

In this example I used amounts to make sure there's "enough" bitcoin for each transaction separately (since if you have 1 BTC and you try to send it twice intuitively see why it shouldn't work).

Assume no extra addresses are generated automatically by the wallet to handle it. I'm talking about this specific re-use of addresses scenario.
Yes, if the second transaction spends the output of the first one, then #2 cannot be confirmed until after #1 is confirmed.  (Though they can be confirmed in a single block, as long as #1 appears before #2 in that block, in which case the confirmations are effectively simultaneous.)

Most miners will consider transactions on a "child pays for parent" basis, so that a low fee for #1 could be compensated by a high fee in #2.  The two transactions would be considered as a single "lump" with their combined fee, and a miner would confirm them if the combined lump pays a higher fee than the next most lucrative transaction (or lump) that could fill that space.