[Core] ModifyNewCoins saves database lookups #1777
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When processing a new transaction, in addition to spending the Coins of its txin's it creates a new Coins for its outputs. The existing ModifyCoins function will first make sure this Coins does not already exist. It can not exist due to BIP 30, but because of that the lookup can't be cached and always has to go to the database. Since we are creating the coins to match the new tx anyway, there is no point in checking if they exist first anyway. However this should not be used for coinbase tx's in order to preserve the historical behavior of overwriting the two existing duplicate tx pairs.
As PIVX started with BIP34 already enforced, there are no duplicate coinbases
(adapted from bitcoin/bitcoin@1cf3dd8, removing the 'spent_a_duplicate_coinbase' checks)
Fuzzbawls
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Aug 8, 2020
random-zebra
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Aug 18, 2020
cdbb1a6 Remove unused variable in test, fixing warning. (Russell Yanofsky) 03031a5 Check FRESH validity in CCoinsViewCache::BatchWrite (Russell Yanofsky) 3fb3e03 Fix dangerous condition in ModifyNewCoins. (random-zebra) 228d6bc [test] Add CCoinsViewCache Access/Modify/Write tests (random-zebra) Pull request description: Going on with the coins view cache update work (started with #1774 and #1777). This backports the following upstream PRs (adapting them with the assumption that duplicate coinbase transactions are not possible): - bitcoin#9308 - [test] Add CCoinsViewCache Access/Modify/Write tests - bitcoin#9107 - Safer modify new coins - bitcoin#9310 - Assert FRESH validity in CCoinsViewCache::BatchWrite - bitcoin#9435 - Removed unused variable in test, fixing warning. Note: Will rebase #1773 on top of this one (to change `ApplyTxInUndo` return value in the unit test too). ACKs for top commit: furszy: pretty nice one, ACK cdbb1a6 Fuzzbawls: ACK cdbb1a6 Tree-SHA512: 69c534da1083c3c4a535923e98da7750474c6698bb45e042778b539a27fab0455d78aaf670bed9485522f9d2ee25e4ad57fa7d35632523fe7376fe5f5febb1e5
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Adapted version of bitcoin#6932
We remove the restriction on coinbases, and thus use always
ModifyNewCoinsinstead ofModifyCoins, since duplicated coinbases are not possible on PIVX (ref. #1775).Accordingly, we remove the logic for checking the effects of duplicate coinbase txs in the unit test.