turbo-persistence: pin referenced BlockCache entries to prevent eviction#92361
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turbo-persistence: pin referenced BlockCache entries to prevent eviction#92361
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lukesandberg
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Apr 6, 2026
…d entries Implement `quick_cache::Lifecycle` for `BlockCacheLifecycle` with `is_pinned` that checks whether the `ArcBytes` backing `Arc` has strong_count > 1, preventing eviction of cache entries still referenced outside the cache. Co-Authored-By: Claude <noreply@anthropic.com>
…lias in tests Drop the Option-based eviction stash since we only need is_pinned. Remove the redundant TestBlockCache type alias in favor of the existing BlockCache alias. Co-Authored-By: Claude <noreply@anthropic.com>
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Co-Authored-By: Claude <noreply@anthropic.com>
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…ion (#92361) ### What? Implements [`quick_cache::Lifecycle`](https://docs.rs/quick_cache/latest/quick_cache/#lifecycle-hooks) hooks for the `BlockCache` in turbo-persistence. A new `BlockCacheLifecycle` struct overrides `is_pinned` to check whether the `ArcBytes` value's backing `Arc` has a strong count > 1, indicating it is still referenced outside the cache. When `is_pinned` returns `true`, the cache's eviction algorithm (Clock-PRO / S3-FIFO) skips the entry instead of evicting it. ### Why? Without pinning, the cache can evict blocks that are still in use — the caller holds an `ArcBytes` clone (which shares the `Arc` backing), so the data isn't lost, but the cache slot is wasted. When the caller finishes and the entry is looked up again, it results in an unnecessary cache miss and re-read/decompress from disk. By checking `Arc::strong_count > 1` in `is_pinned`, we avoid evicting entries that are actively referenced, improving cache hit rates under concurrent access. ### How? **`ArcBytes::is_shared()`** (`arc_bytes.rs`): - Returns `true` when the backing `Arc<[u8]>` has `strong_count > 1` (i.e., someone outside the cache holds a clone). - Mmap-backed entries always return `false` — the mmap `Arc` is shared across all slices from the same file, so checking its `strong_count` would make them permanently unevictable. This is fine because #92390 already drops mmap blocks from the cache entirely. **`BlockCacheLifecycle`** (`static_sorted_file.rs`): - Implements `quick_cache::Lifecycle<(u32, u16), ArcBytes>` with `RequestState = ()`. - `is_pinned` delegates to `val.is_shared()`. - `begin_request` and `on_evict` are no-ops since we only need the pinning behavior. **`BlockCache` type alias** updated to include `BlockCacheLifecycle` as the 5th generic parameter. All call sites use `Default::default()` for construction, so no call-site changes were needed. **Test cleanup**: Removed the redundant `TestBlockCache` type alias (and its unused imports) in the builder tests in favor of the existing `BlockCache` alias. <!-- NEXT_JS_LLM_PR --> --------- Co-authored-by: Tobias Koppers <sokra@users.noreply.github.com> Co-authored-by: Claude <noreply@anthropic.com>
eps1lon
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Apr 7, 2026
…ion (#92361) ### What? Implements [`quick_cache::Lifecycle`](https://docs.rs/quick_cache/latest/quick_cache/#lifecycle-hooks) hooks for the `BlockCache` in turbo-persistence. A new `BlockCacheLifecycle` struct overrides `is_pinned` to check whether the `ArcBytes` value's backing `Arc` has a strong count > 1, indicating it is still referenced outside the cache. When `is_pinned` returns `true`, the cache's eviction algorithm (Clock-PRO / S3-FIFO) skips the entry instead of evicting it. ### Why? Without pinning, the cache can evict blocks that are still in use — the caller holds an `ArcBytes` clone (which shares the `Arc` backing), so the data isn't lost, but the cache slot is wasted. When the caller finishes and the entry is looked up again, it results in an unnecessary cache miss and re-read/decompress from disk. By checking `Arc::strong_count > 1` in `is_pinned`, we avoid evicting entries that are actively referenced, improving cache hit rates under concurrent access. ### How? **`ArcBytes::is_shared()`** (`arc_bytes.rs`): - Returns `true` when the backing `Arc<[u8]>` has `strong_count > 1` (i.e., someone outside the cache holds a clone). - Mmap-backed entries always return `false` — the mmap `Arc` is shared across all slices from the same file, so checking its `strong_count` would make them permanently unevictable. This is fine because #92390 already drops mmap blocks from the cache entirely. **`BlockCacheLifecycle`** (`static_sorted_file.rs`): - Implements `quick_cache::Lifecycle<(u32, u16), ArcBytes>` with `RequestState = ()`. - `is_pinned` delegates to `val.is_shared()`. - `begin_request` and `on_evict` are no-ops since we only need the pinning behavior. **`BlockCache` type alias** updated to include `BlockCacheLifecycle` as the 5th generic parameter. All call sites use `Default::default()` for construction, so no call-site changes were needed. **Test cleanup**: Removed the redundant `TestBlockCache` type alias (and its unused imports) in the builder tests in favor of the existing `BlockCache` alias. <!-- NEXT_JS_LLM_PR --> --------- Co-authored-by: Tobias Koppers <sokra@users.noreply.github.com> Co-authored-by: Claude <noreply@anthropic.com>
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What?
Implements
quick_cache::Lifecyclehooks for theBlockCachein turbo-persistence. A newBlockCacheLifecyclestruct overridesis_pinnedto check whether theArcBytesvalue's backingArchas a strong count > 1, indicating it is still referenced outside the cache.When
is_pinnedreturnstrue, the cache's eviction algorithm (Clock-PRO / S3-FIFO) skips the entry instead of evicting it.Why?
Without pinning, the cache can evict blocks that are still in use — the caller holds an
ArcBytesclone (which shares theArcbacking), so the data isn't lost, but the cache slot is wasted. When the caller finishes and the entry is looked up again, it results in an unnecessary cache miss and re-read/decompress from disk.By checking
Arc::strong_count > 1inis_pinned, we avoid evicting entries that are actively referenced, improving cache hit rates under concurrent access.How?
ArcBytes::is_shared()(arc_bytes.rs):truewhen the backingArc<[u8]>hasstrong_count > 1(i.e., someone outside the cache holds a clone).false— the mmapArcis shared across all slices from the same file, so checking itsstrong_countwould make them permanently unevictable. This is fine because turbo-persistence: skip BlockCache for uncompressed (mmap-backed) blocks #92390 already drops mmap blocks from the cache entirely.BlockCacheLifecycle(static_sorted_file.rs):quick_cache::Lifecycle<(u32, u16), ArcBytes>withRequestState = ().is_pinneddelegates toval.is_shared().begin_requestandon_evictare no-ops since we only need the pinning behavior.BlockCachetype alias updated to includeBlockCacheLifecycleas the 5th generic parameter. All call sites useDefault::default()for construction, so no call-site changes were needed.Test cleanup: Removed the redundant
TestBlockCachetype alias (and its unused imports) in the builder tests in favor of the existingBlockCachealias.