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(note: this is a temporary file, to be added-to by anybody, and moved to
release-notes at release time)
Transaction fee changes
=======================
This release automatically estimates how high a transaction fee (or how
high a priority) transactions require to be confirmed quickly. The default
settings will create transactions that confirm quickly; see the new
'txconfirmtarget' setting to control the tradeoff between fees and
confirmation times.
Prior releases used hard-coded fees (and priorities), and would
sometimes create transactions that took a very long time to confirm.
New Command Line Options
========================
-txconfirmtarget=n : create transactions that have enough fees (or priority)
so they are likely to confirm within n blocks (default: 1). This setting
is over-ridden by the -paytxfee option.
New RPC methods
===============
Fee/Priority estimation
-----------------------
estimatefee nblocks : Returns approximate fee-per-1,000-bytes needed for
a transaction to be confirmed within nblocks. Returns -1 if not enough
transactions have been observed to compute a good estimate.
estimatepriority nblocks : Returns approximate priority needed for
a zero-fee transaction to confirm within nblocks. Returns -1 if not
enough free transactions have been observed to compute a good
estimate.
Statistics used to estimate fees and priorities are saved in the
data directory in the 'fee_estimates.dat' file just before
program shutdown, and are read in at startup.
Double-Spend Relay and Alerts
=============================
VERY IMPORTANT: *It has never been safe, and remains unsafe, to rely*
*on unconfirmed transactions.*
Relay
-----
When an attempt is seen on the network to spend the same unspent funds
more than once, it is no longer ignored. Instead, it is broadcast, to
serve as an alert. This broadcast is subject to protections against
denial-of-service attacks.
Wallets and other bitcoin services should alert their users to
double-spends that affect them. Merchants and other users may have
enough time to withhold goods or services when payment becomes
uncertain, until confirmation.
Bitcoin Core Wallet Alerts
--------------------------
The Bitcoin Core wallet now makes respend attempts visible in several
ways.
If you are online, and a respend affecting one of your wallet
transactions is seen, a notification is immediately issued to the
command registered with `-respendnotify=<cmd>`. Additionally, if
using the GUI:
- An alert box is immediately displayed.
- The affected wallet transaction is highlighted in red until it is
confirmed (and it may never be confirmed).
A `respendsobserved` array is added to `gettransaction`, `listtransactions`,
and `listsinceblock` RPC results.
Warning
-------
*If you rely on an unconfirmed transaction, these change do VERY*
*LITTLE to protect you from a malicious double-spend, because:*
- You may learn about the respend too late to avoid doing whatever
you were being paid for
- Using other relay rules, a double-spender can craft his crime to
resist broadcast
- Miners can choose which conflicting spend to confirm, and some
miners may not confirmg the first acceptable spend they see
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