Occasionally transactions will be broadcast to the network that will show in a 0/unconfirmed status in the Bitcoin client. It is also the case that from time to time for various reasons those transactions will never confirm. One known reason for such unconfirmed transactions is a double-spending attempt, though these are usually quickly resolved by the network. My question is twofold:
- Is there any source of data or is there a known statistic stating what percent of transactions hit 0/unconfirmed and never progress beyond this state (i.e. are resolved as conflicts by the network).
- Is there anything aside from a double-spending attempt that can produce a 0/unconfirmed transaction that does not confirm.
Please note that I am not referring to the "generated" transactions by which miners are paid, but rather a point-to-point transfer of bitcoins.