On Tue, Aug 5, 2014 at 3:10 PM, Kaz Wesley <keziahw@gmail.com> wrote:

Any approach based on beginning a transaction expiry countdown when a
transaction is received (as in mempool janitor) seems unviable to me:

...

That's why I think including information in the transaction itself, as
with my nLockTime/IsStandard proposal, is necessary for transactions
to reliably eventually die off from mempools.

"reliably die off from mempools" leads into the land of "tightly synchronizing memory pools across the network" which is a problem of... large scope and much debate. :)

For the moment, simply capping the mempool's size at each local node is a much more reachable goal. Capping, then, implies some culling policy. In general, bitcoind Tx mempool size is rather open ended, and that needs sorting out.

--
Jeff Garzik
Bitcoin core developer and open source evangelist
BitPay, Inc. https://bitpay.com/