Document caching shard store + test drop/flush different behavior.#185
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Document caching shard store + test drop/flush different behavior.#185dannywillems wants to merge 4 commits into
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Adds the ability to mark a checkpoint for retention so that it is exempt from automatic pruning of excess checkpoints. A retained checkpoint's root, and witnesses for marked leaves at or before it, remain computable even after it has aged more than `max_checkpoints` behind the tip of the tree. Retention is an explicit operation, decoupled from leaf marking: `ShardTree::ensure_retained` records a checkpoint id in a new retention set on the `ShardStore` (`add_retained_checkpoint` / `remove_retained_checkpoint` / `retained_checkpoints`), and `ShardTree::remove_retained_checkpoint` releases it. `prune_excess_checkpoints` excludes retained checkpoints from the `max_checkpoints` budget and never removes them. The witness-supporting nodes survive because the retained checkpoint's own `CHECKPOINT` retention keeps the subtree straddling its position from collapsing; no `Reference` retention is required. See zcash#183. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Co-authored-by: Kris Nuttycombe <kris@nutty.land>
dannywillems
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July 2, 2026 09:18
Explain the deferred-action mechanism in `CachingShardStore`. The store serves reads and additive writes from its in-memory cache and, on `flush`, reconstructs the backend by re-writing the full cached state. That re-write reproduces additions but cannot express removals, so destructive operations are recorded as `Action`s and replayed against the backend before the additive state is written back. Document each `Action` variant with the `ShardStore` removal method it replays, and describe the two-phase flush and the drop-without-flush behavior on the `flush` method. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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Add two tests covering how `CachingShardStore` propagates cached mutations to the backend. The backend is passed to the store as `&mut` (via the blanket `ShardStore for &mut S` impl), so it stays owned by the test and can be inspected once the store, and its borrow, are gone. `flush_persists_to_backend` asserts the backend is populated only after `flush` is called. `drop_without_flush_does_not_persist` lets the store go out of scope without flushing and asserts the backend is never written. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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