1d7935b45a test: add test for coins view flush behavior using Sync() (James O'Beirne)
2c3cbd6c00 test: add use of Sync() to coins tests (James O'Beirne)
6d8affca96 test: refactor: clarify the coins simulation (James O'Beirne)
79cedc36af coins: add Sync() method to allow flush without cacheCoins drop (James O'Beirne)
Pull request description:
This is part of the [assumeutxo project](https://github.com/bitcoin/bitcoin/projects/11):
Parent PR: #15606
Issue: #15605
Specification: https://github.com/jamesob/assumeutxo-docs/tree/master/proposal
---
In certain circumstances, we may want to flush chainstate data to disk without
emptying `cacheCoins`, which affects performance. UTXO snapshot
activation is one such case, as we populate `cacheCoins` with the snapshot
contents and want to persist immediately afterwards but also enter IBD.
See also #15265, which makes the case that under normal operation a
flush-without-erase doesn't necessarily add much benefit. I open this PR
even in light of the previous discussion because (i) flush-without-erase
almost certainly provides benefit in the case of snapshot activation (especially
on spinning disk hardware) and (ii) this diff is fairly small and gives us convenient
options for more granular cache management without changing existing policy.
See also #15218.
ACKs for top commit:
sipa:
ACK 1d7935b45a
achow101:
ACK 1d7935b45a
Sjors:
tACK 1d7935b45a
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82903a7a8d