Sim Compare

Run a comprehensive cache policy comparison for the given trace.

Input

Trace file: $ARGUMENTS

If no policies or sizes are specified, use sensible defaults based on the trace.

Workflow

1. Identify the trace format. Check the file extension and contents:

   • .gz files: try common formats (lirs, arc, etc.)
   • Look at simulator/src/main/resources/reference.conf for format options
   • Use format:path syntax (e.g., lirs:trace.gz)

2. Select policies to compare. Policy names use category.PolicyName format. Note: config categories use hyphens (two-queue, greedy-dual), not underscores. Each policy is paired with configured admission filters (default: Always, TinyLfu, Clairvoyant), creating multiple instances per policy name.

   Include at minimum:

   • product.Caffeine (the production implementation)
   • opt.Clairvoyant (theoretical optimal, upper bound)
   • opt.Unbounded (infinite cache, ceiling)
   • linked.Lru (baseline)
   • sketch.WindowTinyLfu (research W-TinyLFU)
   • sketch.HillClimberWindowTinyLfu (adaptive variant)
   • Add relevant competitors based on trace characteristics:
     • For recency-heavy: linked.S4Lru, adaptive.Arc
     • For frequency-heavy: linked.Lfu, irr.Lirs
     • For scan-resistant: two-queue.TwoQueue, two-queue.S3Fifo
     • For size-aware traces: greedy-dual.Gdsf, greedy-dual.Camp

3. Choose cache sizes. Use a geometric progression covering the working set:

   • Start small (e.g., 100), end near working set size
   • 5-8 sizes: e.g., 100,500,1_000,2_500,5_000,10_000,25_000
   • If the trace has few distinct keys, reduce the range

4. Run the simulation. Use the Gradle task:

   ./gradlew simulator:simulate -q \
     --maximumSize=100,500,1000,2500,5000,10000 \
     --metric="Hit Rate" \
     --title="Description" \
     --theme=light \
     --outputDir=build/reports/sim
   

   Override the trace and policies via system properties appended to the command:

   -Dcaffeine.simulator.files.paths.0="format:path/to/trace"
   -Dcaffeine.simulator.policies.0=product.Caffeine
   -Dcaffeine.simulator.policies.1=opt.Clairvoyant
   # ... etc
   

   Note: for single-size runs, use ./gradlew simulator:run -q with -Dcaffeine.simulator.maximum-size=N instead of simulator:simulate.

5. Read and interpret results. The simulate task produces:

   • Individual CSV per cache size
   • Combined CSV (policies as rows, sizes as columns)
   • PNG chart (line graph of metric vs cache size) Read the CSV output files in the output directory:
   • Compare hit rates across policies at each cache size
   • Identify the crossover points where one policy overtakes another
   • Note the gap between Caffeine and Clairvoyant (theoretical ceiling)

6. Explain findings. For each notable result:

   • WHY does policy X beat policy Y on this trace?
   • What trace characteristic drives the difference? (frequency bias, recency bias, scan patterns, temporal shifts)
   • How close is Caffeine to optimal? Where does it lose?
   • Reference the relevant research paper if applicable:
     • TinyLFU paper for admission filter behavior
     • Adaptive paper for hill climber effectiveness
     • See .claude/docs/research-foundations.md for paper-to-code mapping

7. Report. Present:

   • Summary table of hit rates at each cache size
   • Key takeaways (2-3 sentences)
   • Notable policy behaviors
   • Path to generated chart PNG