[bitcoin-dev] Upcoming Transaction Priority Changes

[Matt Corallo <lf-lists@mattcorallo.com>]

On the IRC meeting today there was a long discussion on how to handle
the old "transaction priority" stuff in 0.12. Over time the "transaction
priority" stuff has added a huge amount of code and taken a bunch of
otherwise-useful developer effort. There is still some debate about its
usefulness going forward, but there was general agreement that it will
either be removed entirely or replaced with something a bit less costly
to maintain some time around 0.13.

With the mempool limiting stuff already in git master, high-priority
relay is disabled when mempools are full. In addition, there was
agreement to take the following steps for 0.12:

 * Mining code will use starting priority for ease of implementation
 * Default block priority size will be 0
 * Wallet will no longer create 0-fee transactions when mempool limiting
is in effect.

What this means for you is, essentially, be more careful when relying on
priority to mine your transactions. If mempools are full, your
transactions will be increasingly less likely to be relayed and more
miners may start disabling high-priority block space. Make sure you
analyze previous blocks to determine if high-priority mining is still
enabled and ensure your transactions will be relayed.

Matt