pdftract/notes/pdftract-5mhe8.md

Phase 6.9 Coordinator Verification Note

Bead ID

pdftract-5mhe8

Summary

All 6 child task beads for the Content-Addressed Cache Layer have been completed and verified. The cache implementation is complete and tested.

Child Beads Closed

1. pdftract-172kr (6.9.1): Filesystem layout - CLOSED
2. pdftract-375xa (6.9.2): Cache key construction - CLOSED
3. pdftract-2xql8 (6.9.3): zstd compression encode/decode - CLOSED
4. pdftract-15prh (6.9.4): LRU eviction policy - CLOSED
5. pdftract-15pz8 (6.9.5): Multi-process safety - CLOSED
6. pdftract-2i6rt (6.9.6): cache subcommand + CLI flags + HTTP header - CLOSED

Acceptance Criteria Status

Module Structure

• crates/pdftract-core/src/cache/ module exists with:

  • layout.rs - Path construction (cache_dir/fp[0:2]/fp[2:4]/full_fp/)
  • key.rs - Cache key from (fingerprint, canonical options JSON SHA-256)
  • compression.rs - zstd encode/decode
  • lru.rs - LRU eviction with O_APPEND sentinel
  • multi_process.rs - Atomic temp+rename writes
  • mod.rs - Module coordination

• crates/pdftract-cli/src/cache_cmd.rs - cache subcommand (stats/clear/purge)

CLI Flags

• --cache-dir <DIR> - Enable cache at directory
• --cache-size <SIZE> - Set cache size limit (default 1 GiB)
• --no-cache - Disable cache for this extraction

HTTP Integration

• X-Pdftract-Cache: hit | miss | skipped header on all serve endpoints

Cache Tests

All 92 cache tests pass:

• cache::layout::* - Path construction tests
• cache:🔑:* - Cache key construction tests
• cache::compression::* - zstd compression tests
• cache::lru::* - LRU eviction tests
• cache::multi_process::* - Atomic write and concurrent access tests

Critical Tests (from plan)

1. Hit-then-modify: Content edit → cache miss (verified via fingerprint change)
2. Hit-then-touch-metadata: Metadata-only edit → cache hit (same fingerprint)
3. Concurrent extractors: test_concurrent_writers_same_key - both succeed, no deadlock
4. LRU eviction: test_eviction_sweep_performance - evicts oldest, new writes succeed
5. Empty cache stats: cache stats on empty dir reports zero entries
6. Corrupt entry: test_acceptance_corrupt_entry_treated_as_miss - deleted, extraction re-runs

Performance Considerations

• Cache hit target: < 20 ms p99 on 100-page PDF (filesystem-bound O(1) lookup)
• Concurrent hit target: > 10,000 req/s on commodity SSD (no contention via O_APPEND)
• Process restart: Cache survives (filesystem-only state)

Verification Commands

# Cache module structure
ls -la crates/pdftract-core/src/cache/

# Cache CLI subcommand
./target/debug/pdftract cache --help
./target/debug/pdftract cache stats /tmp/test-cache

# Cache flags on extract
./target/debug/pdftract extract --help | grep -E "cache|no-cache"

# Run cache tests
cargo test --package pdftract-core --lib cache

Implementation Notes

• Cache key includes extraction_version to force cache miss on binary upgrade
• NDJSON streaming mode populates cache but does NOT serve from cache (per plan)
• Multi-process safety via atomic temp+rename; duplicated work on race is tolerated
• LRU touched-time via O_APPEND sentinel (no per-entry stat churn)
• Corrupt entries (truncated/zstd-fail) treated as miss and deleted

Related Commits

• d9a5fe6 feat(pdftract-2i6rt): implement cache CLI subcommand and HTTP integration
• f8cf8f1 docs(pdftract-15pz8): add verification note for multi-process safe cache operations
• 8c9a940 feat(pdftract-15pz8): implement multi-process safe cache operations
• b1667db docs(pdftract-15prh): add verification note for LRU eviction implementation
• 0a83ef9 fix(pdftract-15prh): fix LRU eviction test with valid 64-char opts hashes
• d873136 feat(pdftract-2xql8): implement zstd compression encode/decode
• 6cf2d60 feat(pdftract-375xa): implement cache key construction
• 624fc49 feat(pdftract-172kr): implement filesystem layout for cache directory

Status

PASS - All acceptance criteria met. Coordinator bead ready to close.