every other change address is unused

dooglus commented at 4:50 pm on February 6, 2023: contributor

I’m seeing 50% of generated change addresses not being used. It’s as if two are reserved for every one that is used.

This is happening in version v24.0.1.

Here’s a sequence of commands that shows what I mean. Only the odd numbered change hdkeypaths are used:

 0$ /bin/rm -fr ~/.bitcoin/regtest
 1$ bitcoin-qt -regtest &
 2$ bitcoin-cli -regtest createwallet 1 > /dev/null
 3$ bitcoin-cli -regtest createwallet 2 > /dev/null
 4$ bitcoin-cli -regtest -rpcwallet=1 -generate 1 > /dev/null
 5$ bitcoin-cli -regtest -rpcwallet=2 -generate 100 > /dev/null
 6$ to=$(bitcoin-cli -regtest -rpcwallet=2 getnewaddress)
 7$ txs=$(for i in {1..5}; do bitcoin-cli -regtest -rpcwallet=1 sendtoaddress $to 1; done)
 8$ addrs=$(for i in $txs; do bitcoin-cli -regtest getrawtransaction $i true | jq -Mc '.vout[]|{value:.value,addr:.scriptPubKey.address}'; done | grep -v ':1,' | jq -r .addr)
 9$ for a in $addrs; do bitcoin-cli -regtest -rpcwallet=1 getaddressinfo $a | jq -r .hdkeypath; done
10m/84'/1'/0'/1/1
11m/84'/1'/0'/1/3
12m/84'/1'/0'/1/5
13m/84'/1'/0'/1/7
14m/84'/1'/0'/1/9

This happens whether or not I create descriptor wallets. For example, with a descriptor wallet I get these descriptors for the change addresses:

0wpkh([779aecf0/84'/1'/0'/1/1]029919052bd5b904afbf71d90afbec0a852d1f0181914b6d07bcab028a0d1ac3e4)#94rhf9lu
1wpkh([779aecf0/84'/1'/0'/1/3]0360ecbba4ebaac3ab4f62f14b12a136c2cc5e8264ac1be2af1b5e4413944a2c6a)#lwjzrh62
2wpkh([779aecf0/84'/1'/0'/1/5]03d3f72c2cc6085bdee5388ff3b96df7d27ac18d85b5cc8d8048e287b52777062e)#5q4fsvmd
3wpkh([779aecf0/84'/1'/0'/1/7]02b77a29387f645bb5ed27ef25144ae67a984e056e41b35fce33bb377d199845ab)#mc608kvz
4wpkh([779aecf0/84'/1'/0'/1/9]024988fafba17c2d6f5b2b27428e2fb65ca8a7882ac0fae1422e4fdf46c95dbc61)#mwxzye2v

and for a legacy wallet I get these:

0wpkh([bcc40f8d/0'/1'/1']03d3cc823cd01dcb23dce0ac53f8b38c3cb8b9ddbdfc789550c280d25cba432932)#3vxlglf6
1wpkh([bcc40f8d/0'/1'/3']03016e2243892459754e125954d205136247f67580e9379ca931f2ec374b924aef)#kxwx63p3
2wpkh([bcc40f8d/0'/1'/5']0236dd8b3a6ebd26a4e1e9dc1d84bf053438c339babacd202000f44917bd452336)#jaq2hgn4
3wpkh([bcc40f8d/0'/1'/7']03785884e52fad4588d2d0e1df48b8ba691dddfb3696667932a3b46cb0202132fa)#0d786n6s
4wpkh([bcc40f8d/0'/1'/9']03ba88cdc9a37aa676a1152c6d7d970aa32324b99d8c6f775c4543e016161ea4d9)#vdvr44ar

dooglus added the label Bug on Feb 6, 2023

achow101 commented at 5:03 pm on February 6, 2023: member

For anyone who wants to tackle this, it’s most likely to be the optimistic avoidpartialspends behavior which does transaction creation twice, and in doing so, also retrieves two change addresses.

pinheadmz commented at 5:09 pm on February 6, 2023: member

For anyone who wants to tackle this

Taking a look now ;-)

dooglus commented at 6:08 pm on February 6, 2023: contributor

If I specify -avoidpartialspends on the bitcoin-qt commandline I don’t see the wasted change addresses.

pinheadmz commented at 8:41 pm on February 6, 2023: member

Possible fix: #27053 @dooglus are you able to test/review ?

dooglus commented at 11:16 pm on February 6, 2023: contributor

@pinheadmz I’m not familiar enough with the code to review it, but I’ve tested it and it works for me with both legacy and descriptor wallets.

every other change address is unused #27051