[Layered Map] Expose inner layers #18353
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Previously, in order to find all changes between two `State`s, we could just "diff" the two map layers and we would get all the KVs that are changed. This is insufficient with tiered storage. For instance, consider the following sequence of events: 1. At the end of block `N`, key `K` is read and promoted to hot and its value is `V0` in both hot state and cold state. 2. At the end of block `N+1`, its value is updated to `V1` in hot state. 3. At the end of block `N+2`, it's evicted and the value in cold state is updated to `V1`. 4. At the end of block `N+3`, it's read and promoted into hot state again. If we simply look at the `StateDelta` in the current implementation, we'd see the value change in hot state, but miss the change from `V0` to `V1` in the cold state. So we need to expose all the inner layers in order to accurately compute what changed between two points in time. This PR simply adds the API on `LayeredMap`.
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Previously, in order to find all changes between two
States, we could just "diff" the two map layers and we would get all the KVs that are changed.This is insufficient with tiered storage. For instance, consider the following sequence of events:
N, keyKis read and promoted to hot and its value isV0in both hot state and cold state.N+1, its value is updated toV1in hot state.N+2, it's evicted and the value in cold state is updated toV1.N+3, it's read and promoted into hot state again.If we simply look at the
StateDeltain the current implementation, we'd see the value change in hot state, but miss the change fromV0toV1in the cold state.So we need to expose all the inner layers in order to accurately compute what changed between two points in time. This PR simply adds the API on
LayeredMap.Note
Introduces per-layer views and parent linking to support inspecting all changes between two layers.
parent: Weak<Self>toLayerInnerand set it innew_family/spawn; children remain tracked for drop safetyMapLayer::parent()to navigate layer ancestryLayeredMap::inner_maps()returning the sequence of inner maps between(base_layer, top_layer]in ordernaive_view_layer, verifyinner_maps()correctness forget()anditer()Written by Cursor Bugbot for commit 651ec78. This will update automatically on new commits. Configure here.