Ludovic Marie
4.1 KiB
Heap budget experiment
Halving the maximum Java heap from 3 GiB to 1.5 GiB does not halve total process RAM in this workload. Three repeated core-profile pairs show nearly unchanged average FPS and variable sampled RSS reductions, with more GC accounting time in every smaller-heap run. Playable memory recommendations remain unchanged.
Matched experiment
These runs use the exact published 0.20.0 mod and the same private camera fixture as the repeated core comparison. Both sides use the core stack, 12 full-detail / 12 simulation chunks, 1280×800, FOV 70, uncapped FPS, OpenGL, no LOD/shaders, G1 and compact headers. Only maximum heap differs. The initial heap is 512 MiB in both sides. Every run uses a fresh process and the same initial world copy, warms for 180 seconds and records for 120 seconds. Each pair runs 3 GiB first, followed by 1.5 GiB.
The host is an i7-7500U with 2 physical cores / 4 logical processors and about 30.2 GiB total RAM, using Linux llvmpipe software rendering. This is not a test under low system-memory pressure. Private copies use Peaceful difficulty and fixed noon/weather advancement rules. The camera is stationary and every original experimental controller is disabled. Those fixture rules are absent from playable packs.
Results
| Pair | 3 GiB FPS | 1.5 GiB FPS | 3 GiB peak RSS | 1.5 GiB peak RSS | 3 GiB p95 frame | 1.5 GiB p95 frame | GC accounting |
|---|---|---|---|---|---|---|---|
| 1 | 6.4549 | 6.5133 | 2,080.07 MiB | 2,041.48 MiB | 166.26 ms | 173.65 ms | 95 → 162 ms |
| 2 | 6.5528 | 6.5115 | 2,482.75 MiB | 1,997.45 MiB | 166.18 ms | 174.22 ms | 72 → 93 ms |
| 3 | 6.5624 | 6.5556 | 2,242.84 MiB | 1,989.43 MiB | 166.55 ms | 165.82 ms | 71 → 105 ms |
Paired average-FPS changes are +0.90%, −0.63%, −0.10%. Their descriptive arithmetic mean is +0.06%; this does not establish an FPS improvement. Peak sampled RSS is 1.86%, 19.55% and 11.30% lower, illustrating substantial process variation. A smaller configured heap limit is not a total resident-memory cap. The smaller-heap captures still use roughly 1.94–1.99 GiB of sampled process RSS.
p95 frame intervals are 4.44% and 4.84% worse in the first two pairs and 0.44% better in the third. Slowest-1%-average FPS changes are −0.06%, −5.08%, +10.03%. CPU changes are −5.10%, +0.24%, −0.17%, without a consistent absolute reduction. GC accounting time increases 29–71%; these MXBean totals are not measured stop-the-world pause durations. Tick execution means change −7.25%, +9.22%, +1.15%, while observed invocation throughput stays near 20 TPS in every run.
Validation and limits
All six clients save and exit with code zero. Frame/tick CSV counts and mean durations match their JSONs, with zero exclusions or dropped samples. Captured settings, Java/collector/header configuration and loaded mod identities match apart from the intentional heap maximum. Sampled tick-manager state remains normal at 20 configured TPS, without freeze, step, sprint or rate changes. Saved camera, position, clock and weather rules match across runs.
All three actual frame/tick JSON+CSV pairs pass desktop/mobile viewer checks, including duration traces and the visible intentional heap mismatch. The selected observations retain all six runs, paired metrics, configuration, software identity and private capture/fixture hashes. Raw worlds, CSVs and complete logs remain private.
These are sampled peaks during settled recordings, not whole-session startup peaks or complete GPU/unified-memory accounting. Three fixed-order pairs in one world cannot establish capacity for exploration, generation, long sessions, shaders, distant terrain, all hardware or 50 dedicated-server players. JIT, OS cache, entities and thermal effects can still vary. Do not pool this experiment with vanilla/core comparisons or infer physical M2 results from it.
The 16 GB Mac starter retains its 6 GiB recommendation for balanced distant terrain. See the Mac test procedure and memory measurement limits when measuring another budget.