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(note: this is a temporary file, to be added-to by anybody, and moved to
release-notes at release time)
estimatefee / estimatepriority RPC methods New RPC methods: return an estimate of the fee (or priority) a transaction needs to be likely to confirm in a given number of blocks. Mike Hearn created the first version of this method for estimating fees. It works as follows: For transactions that took 1 to N (I picked N=25) blocks to confirm, keep N buckets with at most 100 entries in each recording the fees-per-kilobyte paid by those transactions. (separate buckets are kept for transactions that confirmed because they are high-priority) The buckets are filled as blocks are found, and are saved/restored in a new fee_estiamtes.dat file in the data directory. A few variations on Mike's initial scheme: To estimate the fee needed for a transaction to confirm in X buckets, all of the samples in all of the buckets are used and a median of all of the data is used to make the estimate. For example, imagine 25 buckets each containing the full 100 entries. Those 2,500 samples are sorted, and the estimate of the fee needed to confirm in the very next block is the 50'th-highest-fee-entry in that sorted list; the estimate of the fee needed to confirm in the next two blocks is the 150'th-highest-fee-entry, etc. That algorithm has the nice property that estimates of how much fee you need to pay to get confirmed in block N will always be greater than or equal to the estimate for block N+1. It would clearly be wrong to say "pay 11 uBTC and you'll get confirmed in 3 blocks, but pay 12 uBTC and it will take LONGER". A single block will not contribute more than 10 entries to any one bucket, so a single miner and a large block cannot overwhelm the estimates.
9 years ago
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 confirm the first acceptable spend they see