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S3 Cache Simulation

The s3_cache_sim binary drives the cache via direct S3 trait calls (no HTTP) with a simulated backend, allowing reproducible benchmarking of hit rates and latency under various workloads. Build it with the sim feature:

cargo build --release --bin s3_cache_sim --features sim

Run --help for all available flags:

cargo run --release --bin s3_cache_sim --features sim -- --help

Scenarios

1. No cache (baseline) — Bypass the cache entirely with --no-cache to establish a raw backend latency baseline. Compare against cached runs to measure the actual speedup.

cargo run --release --bin s3_cache_sim --features sim -- \
  --no-cache

2. Zipf baseline — Realistic workload with moderate skew (s=1.0). Compare against scenario 1 to see the cache's effect.

cargo run --release --bin s3_cache_sim --features sim

3. Heavy skew — High Zipf exponent (s=1.5) concentrates requests on a small hot set, demonstrating near-optimal hit rates.

cargo run --release --bin s3_cache_sim --features sim -- \
  --zipf-exponent 1.5

4. Scan resistance — Sequential scan over 10K objects. S3-FIFO should resist pollution, yielding ~0% hit rate (which is correct behavior — an LRU would thrash and waste memory).

cargo run --release --bin s3_cache_sim --features sim -- \
  --pattern scan

5. One-hit-wonders — 30% of requests go to unique keys never seen again. Tests the cache's ability to avoid wasting capacity on transient objects.

cargo run --release --bin s3_cache_sim --features sim -- \
  --one-hit-wonder-ratio 0.3

6. Tiny cache under pressure — Only 100 cache entries and 1MB budget. Measures how gracefully hit rate degrades when the cache is severely undersized.

cargo run --release --bin s3_cache_sim --features sim -- \
  --cache-max-entries 100 --cache-max-size 1000000

7. Size-constrained eviction — Large objects (50KB-200KB) with the default 10MB cache budget. The byte limit kicks in well before the entry limit, forcing size-aware eviction.

cargo run --release --bin s3_cache_sim --features sim -- \
  --min-object-size 50000 --max-object-size 200000

8. Uniform random — No access skew. With the cache holding 10% of the object set, hit rate reflects pure capacity ratio. Measures baseline behavior without a hot set.

cargo run --release --bin s3_cache_sim --features sim -- \
  --pattern uniform

9. High-latency backend — Simulates a slow upstream (50ms RTT, 10MB/s throughput). Cache hits become dramatically faster than misses, making the latency p50/p99 split clearly visible. Uses fewer requests to keep runtime reasonable.

cargo run --release --bin s3_cache_sim --features sim -- \
  --latency-ms 50 --throughput-bytes-per-sec 10000000 \
  --num-requests 10000