From 9765b17c16413a21c401f7616e69b0c4f5bbf1f4 Mon Sep 17 00:00:00 2001 From: fanquake Date: Wed, 29 Jun 2022 15:55:31 +0100 Subject: [PATCH] Merge bitcoin/bitcoin#25495: Revert "bnb: exit selection when best_waste is 0" MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit af56d63eca8a246c02506c2aef7ea8a22e2d07bb Revert "bnb: exit selection when best_waste is 0" (Murch) Pull request description: This reverts commit 9b5950db8683f9b4be03f79ee0aae8a780b01a4b. Waste can be negative. At feerates lower than long_term_feerate this means that a waste of 0 may be a suboptimal solution and this causes the search to exit prematurely. Only when the feerate is equal to the long_term_feerate would achieving a waste of 0 indicate that we have achieved an optimal solution, because it would mean that the excess is 0. It seems unlikely that this would ever occur outside of test cases, and even then we should prefer solutions with more inputs over solutions with fewer according to previous decisions—but solutions with more inputs are found later in the branch exploration. The "optimization" described in #18257 and implemented in #18262 is therefore a premature exit on a suboptimal solution and should be reverted. ACKs for top commit: sipa: utACK af56d63eca8a246c02506c2aef7ea8a22e2d07bb S3RK: utACK af56d63eca8a246c02506c2aef7ea8a22e2d07bb achow101: ACK af56d63eca8a246c02506c2aef7ea8a22e2d07bb glozow: utACK af56d63eca8a246c02506c2aef7ea8a22e2d07bb, agree it is incorrect to stop here unless we could rule out the possibility of a better solution with negative waste. `SelectCoinsBnB` doesn't know what long term feerate and effective feerate are (and probably shouldn't) so it's better to have no exit early condition at all. Tree-SHA512: 470f1a49041a0042cb69d239fccac7512ace79871d43508b6e7f7a2f3aca3523930b16e00c5513b816d5fe078d9ab53e42b0a80fd3c3d48e6434f24c2b009077 --- src/wallet/coinselection.cpp | 3 --- src/wallet/test/coinselector_tests.cpp | 7 ++++--- 2 files changed, 4 insertions(+), 6 deletions(-) diff --git a/src/wallet/coinselection.cpp b/src/wallet/coinselection.cpp index 359bb0677149..7d66d9dfa892 100644 --- a/src/wallet/coinselection.cpp +++ b/src/wallet/coinselection.cpp @@ -108,9 +108,6 @@ std::optional SelectCoinsBnB(std::vector& utxo_poo best_selection = curr_selection; best_selection.resize(utxo_pool.size()); best_waste = curr_waste; - if (best_waste == 0) { - break; - } } curr_waste -= (curr_value - selection_target); // Remove the excess value as we will be selecting different coins now backtrack = true; diff --git a/src/wallet/test/coinselector_tests.cpp b/src/wallet/test/coinselector_tests.cpp index 435d796a4054..d99c1626a7d5 100644 --- a/src/wallet/test/coinselector_tests.cpp +++ b/src/wallet/test/coinselector_tests.cpp @@ -206,8 +206,8 @@ BOOST_AUTO_TEST_CASE(bnb_search_test) expected_result.Clear(); // Select 5 Cent - add_coin(4 * CENT, 4, expected_result); - add_coin(1 * CENT, 1, expected_result); + add_coin(3 * CENT, 3, expected_result); + add_coin(2 * CENT, 2, expected_result); const auto result3 = SelectCoinsBnB(GroupCoins(utxo_pool), 5 * CENT, 0.5 * CENT); BOOST_CHECK(result3); BOOST_CHECK(EquivalentResult(expected_result, *result3)); @@ -232,8 +232,9 @@ BOOST_AUTO_TEST_CASE(bnb_search_test) // Select 10 Cent add_coin(5 * CENT, 5, utxo_pool); - add_coin(5 * CENT, 5, expected_result); add_coin(4 * CENT, 4, expected_result); + add_coin(3 * CENT, 3, expected_result); + add_coin(2 * CENT, 2, expected_result); add_coin(1 * CENT, 1, expected_result); const auto result5 = SelectCoinsBnB(GroupCoins(utxo_pool), 10 * CENT, 0.5 * CENT); BOOST_CHECK(result5);