This disentangles the script validation skipping from checkpoints.
A new option is introduced "assumevalid" which specifies a block whos
ancestors we assume all have valid scriptsigs and so we do not check
them when they are also burried under the best header by two weeks
worth of work.
Unlike checkpoints this has no influence on consensus unless you set
it to a block with an invalid history. Because of this it can be
easily be updated without risk of influencing the network consensus.
This results in a massive IBD speedup.
This approach was independently recommended by Peter Todd and Luke-Jr
since POW based signature skipping (see PR#9180) does not have the
verifiable properties of a specific hash and may create bad incentives.
The downside is that, like checkpoints, the defaults bitrot and older
releases will sync slower. On the plus side users can provide their
own value here, and if they set it to something crazy all that will
happen is more time will be spend validating signatures.
Checkblocks and checklevel are also moved to the hidden debug options:
Especially now that checkblocks has a low default there is little need
to change these settings, and users frequently misunderstand them as
influencing security or IBD speed. By hiding them we offset the
space added by this new option.
0c50909 testcases: explicitly specify transaction version 1 (John Newbery)
b7e144b Add test cases to test new bitcoin-tx functionality (jnewbery)
61a1534 Add all transaction output types to bitcoin-tx. (jnewbery)
1814b08 add p2sh and segwit options to bitcoin-tx outscript command (Stanislas Marion)
4e7e2e1 Update RPC argument names (John Newbery)
481f289 rpc: Named argument support for bitcoin-cli (Wladimir J. van der Laan)
9adb4e1 rpc: Argument name consistency (Wladimir J. van der Laan)
8d713f7 rpc: Named arguments for rawtransaction calls (Wladimir J. van der Laan)
37a166f rpc: Named arguments for wallet calls (Wladimir J. van der Laan)
78b684f rpc: Named arguments for mining calls (Wladimir J. van der Laan)
b8ebc59 rpc: Named arguments for net calls (Wladimir J. van der Laan)
2ca9dcd test: Add test for RPC named arguments (Wladimir J. van der Laan)
fba1a61 rpc: Named arguments for misc calls (Wladimir J. van der Laan)
286ec08 rpc: Add 'echo' call for testing (Wladimir J. van der Laan)
495eb44 rpc: Named arguments for blockchain calls (Wladimir J. van der Laan)
6f1c76a rpc: Support named arguments (Wladimir J. van der Laan)
5865d41 authproxy: Add support for RPC named arguments (Wladimir J. van der Laan)
5113474 wallet: Use CDataStream.data() (Wladimir J. van der Laan)
e2300ff bench: Use CDataStream.data() (Wladimir J. van der Laan)
adff950 dbwrapper: Use new .data() method of CDataStream (Wladimir J. van der Laan)
a2141e4 streams: Remove special cases for ancient MSVC (Wladimir J. van der Laan)
af4c44c streams: Add data() method to CDataStream (Wladimir J. van der Laan)
20449ef Don't overpay fee if we have selected new coins that result in a smaller transaction. (Alex Morcos)
42f5ce4 Try to reduce change output to make needed fee in CreateTransaction (Alex Morcos)
032ba3f RPC help documentation for addnode peerinfo. (Gregory Maxwell)
90f13e1 Add release notes for addnode changes. (Gregory Maxwell)
50bd12c Break addnode out from the outbound connection limits. (Gregory Maxwell)
On repeated calls to SelectCoins we try to meet the fee necessary for the last transaction, the new fee required might be smaller, so increase our change by the difference if we can.
Once we've picked coins and dummy-signed the transaction to calculate fee, if we don't have sufficient fee, then try to meet the fee by reducing change before resorting to picking new coins.
Gregory Maxwell