Rewrite segcache segments with atomic fields and mmap backing#11
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brayniac merged 5 commits intopelikan-io:mainfrom Apr 18, 2026
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Replace the segment infrastructure with new code that uses atomic types for all mutable header fields and mmap-backed storage via memmap2. Key changes: - SegmentHeader fields are now AtomicI32/AtomicU32/AtomicU8/AtomicInstant, enabling shared-reference access (&self instead of &mut self) - Segment<'a> holds &'a SegmentHeader (shared ref) instead of &'a mut, simplifying get_mut_pair() since headers can alias freely - Segment data heap uses memmap2::MmapMut instead of Box<[u8]> - Boolean accessible/evictable flags replaced with SegmentState enum (Free, Filling, Active, Draining) stored in AtomicU8 - SegmentPool enum (Main, Admission) for S3-FIFO stored in AtomicU8 - fetch_add on write_offset for future concurrent appends - clocksource::coarse::AtomicInstant for create_at/merge_at timestamps Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
- Builder validation is now in build() instead of panicking setters - Added SegmentTooSmall and InvalidHeapSize error variants - Added Mmap variant wrapping std::io::Error for mmap failures - Removed Segments size assertion (MmapMut size is platform-dependent) Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
The third row is the last — padding is 26 bytes contiguous, not split across two rows. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
thinkingfish
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Apr 18, 2026
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Summary
segments/with atomic header fields and mmap-backed storageSegmentHeaderusesAtomicI32/AtomicU32/AtomicU8/AtomicInstantfor all mutable fieldsSegment<'a>now holds&'a SegmentHeader(shared ref) instead of&'a mut— all mutations via atomicsmemmap2::MmapMutinstead ofBox<[u8]>accessible/evictablebooleans replaced withSegmentStateenum (Free,Filling,Active,Draining)get_mut_pair()simplified — headers can alias freely, only data slices need splittingfetch_addon write_offset prepares for future concurrent appendsTest plan
cargo test -p segcache— 54 tests passcargo test -p segcache --features debug— 55 tests pass (magic feature)cargo test -p segcache --features loom -- loom— 8 loom tests passcargo clippy -p segcache --all-features --all-targets -- -D warnings— cleancargo fmt --all --check— clean🤖 Generated with Claude Code