Coins Cache Cleanup checklist #34280

1. 
   l0rinc commented at 10:23 am on January 14, 2026: contributor

   The coins cache (the CCoinsView* stack, CCoinsViewCache, and friends) is a correctness- and performance-critical part of validation, IBD, and assumeutxo. Over time it has accumulated subtle invariants and legacy states (around cache entry flags, spent coin handling, and error catching), and we have been chipping away at it through focused refactors, bugfixes, tests, and performance work.

   This issue tracks the related PRs to help reviewers see how they fit together. The overall aim is fewer error cases, cleaner cache layering, and parallel validation.

   PRs needing review

   Remove invalid cache states

   • #33018 - remove unreachable FRESH-but-not-DIRTY state.

   Simplify view hierarchy

   • #34124 - make CCoinsView purely virtual, add explicit CCoinsViewEmpty.
   • #34320 - replace HaveCoin() with GetCoin().
   • #34132 - inline error catcher into CCoinsViewDB, simplify hot path.

   Isolate block connection

   • #34165 - add non-mutating PeekCoin() to avoid polluting the main cache.

   Flush behavior

   • #33512 - track dirty entries so flush progress reflects actual writes.

   Parallel coin fetching

   • #31132 - async input prefetch during ConnectBlock.

   Other

   • #33854 - fix assumevalid ignored during reindex (see #31494).
   • #32317 - move UTXO access to SpendBlock (kernel API, Utreexo, SwiftSync).

   Recently merged

   • #33680 - split FORCE_SYNC/FORCE_FLUSH, keep cache warm for scantxoutset/gettxoutsetinfo/snapshots.
   • #34164 - add Reset() and reusable view to discard failed connects cheaply.
   • #34207 - ensure GetCoin() only returns unspent coins, align tests with production.
   • #33866 - remove always-true return from BatchWrite.
   • #33657 - allow reading partial block data (useful for bindex).
   • #33602 - reduce map lookups in BatchWrite.
   • #33333 - warn when -dbcache exceeds RAM cap.

   IRC context: https://bitcoin-irc.chaincode.com/bitcoin-core-dev/2026-01-08

2. l0rinc renamed this:
   Coins Cache Cleanup tracking issue
   Coins Cache Cleanup checklist
   on Jan 14, 2026
3. willcl-ark added the label Tracking Issue on Jan 14, 2026
4. 
   sedited commented at 5:48 pm on January 18, 2026: contributor

   The issue seems a bit overladen - I don’t think listing all these PRs is useful. Maybe distill this down to just the coins-related PRs? The benefit I would expect from this issue is that I can connect the various PRs touching the coins and see how they relate to each other. Maybe to add to the benefits in the opening paragraph a bit: Fewer error cases, more ergonomic cache layering, and preparation for asynchronous operations.
5. 
   l0rinc commented at 6:27 pm on January 18, 2026: contributor

   Thanks for the suggestions @sedited and @andrewtoth. Updated the tracker and grouped the PRs - hopefully this helps reviewers see the structure (though many conflict or overlap depending on merge order). I put cleanups first since they’d let us avoid ugly hacks in the larger PRs, culminating in the parallel input fetcher. Let me know what else to adjust.

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l0rinc sedited

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