If you have any change from your transaction, you can send the change to another address that you own with enough fee to cover both transactions and that may get your transaction confirmed.
child-pays-for-parent is not implemented by miners
Hmm that's something I thought existed. It would profit miners to implement this; why don't they?
If Replace By Fee were standard, no transaction would ever be instant, even very small ones. Some see this as an improvement in security at the expense of convenience and choice, others see the improvement in security to be so minuscule, especially with small transactions, that the cost in convenience makes it not worthwhile (although I'm probably summarizing all this incorrectly).
Replace-by-fee, combined with child-pays-for-parent, seems to make 0/unconfirmed transactions much more secure for small transactions. Just read the thread where Peter Todd describes the proposal; he has a very well thought-out argument for why, which I'll summarize:
Current system:
- If a scamer manages to send out a double-spend transaction at the same time as you send the actual transaction, 50% chance yours is confirmed 50% theirs - theirs might even have a higher chance if it has higher fees and a miner (but not most clients) is implementing replace-by-fee.
- Expected value for potential scamer: 0.5*amount_paid
- Expected value for you: amount_paid - P(payee is not a scamer)*amount_paid
Replace-By-Fee system:
- If a scamer sends out a double-spend transaction at the same time as you send the actual transaction, you send another transaction paying the output of your transaction to a transaction fee. Scamer receives nothing, but neither do you.
- Expected value for potential scamer: 0
- Expected value for you: amount_paid
As you can see, there's no longer any motivation to scam. The only reason there would be motivation to scam is if the scamer has a vendetta against you, and if losing the money would cause significant damage you wait for a confirmation - which should be true now anyway.
Potential flaw, you double spend accidential yourself. I managed to do that too...