There is currently little in place for managing transaction lifetime in the network's mempools (see discussion in github in #3722 "mempool transaction expiration", and it seems to be a major factor blocking some mempool exchange, see #1833/1918, #3721). Expiry per-node a certain amount of wall time after receipt has been proposed, but that's a fragile mechanism -- a single node could keep all relayable transactions alive forever by remembering transactions until most nodes have dropped them and then releasing them back into the wild.
I have a proposal for a way to add finite and predictable lifespans to transactions in mempools: we d̶e̶s̶t̶r̶o̶y̶ ̶t̶h̶e̶ ̶r̶e̶s̶u̶r̶r̶e̶c̶t̶i̶o̶n̶ ̶h̶u̶b̶ use nLockTime and a new standardness rule. It could be done in stages, would not necessarily require even a soft fork, and does not cause problems with reorgs like the proposal in #3509: 1. start setting nLockTime to the current height by default in newly created transactions (or slightly below the current height, for reorg-friendliness) 2. once users have had some time to upgrade to clients that set nLockTime, start discouraging transactions without nLockTime -- possibly with a slightly higher fee required for relay 3. start rate-limiting relay of transactions without an nLockTime (maybe this alone could be used to achieve [2]) 4. add a new IsStandard rule rejecting transactions with an nLockTime more than N blocks behind the current tip (for some fixed value N, to be determined) Transactions would stop being relayed and drop out of mempools a fixed number of blocks from their creation; once that window had passed, the sender's wallet could begin to expect the transaction would not be confirmed. In case a reorg displaces a transaction until after its expiry height, a miner can still put it back in the blockchain; the expiry height is just a relay rule. Also, a user who needed to get their original "expired" transaction confirmed could still do so by submitting it directly to a miner with suitable policies. ------------------------------------------------------------------------------ Want fast and easy access to all the code in your enterprise? Index and search up to 200,000 lines of code with a free copy of Black Duck Code Sight - the same software that powers the world's largest code search on Ohloh, the Black Duck Open Hub! Try it now. http://p.sf.net/sfu/bds _______________________________________________ Bitcoin-development mailing list Bitcoin-development@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/bitcoin-development
