The 626 Megabyte Clue: How a Single ls -lh Command Unlocked the Circuit Size Puzzle

Introduction

In the course of a deep-dive investigation into Filecoin's SUPRASEAL_C2 Groth16 proof generation pipeline, a single message stands out as a quiet turning point. Message [msg 36] appears, on its surface, to be a routine check: the assistant wants to look at actual parameter file sizes on disk. It runs an ls -lh command against the Filecoin proof parameters cache directory, filters for files matching "spacetime" or "sector-update", and pipes the output through head -30. The result is a sparse listing of three files: two verification keys at 1.4 kilobytes each, and one .params file weighing in at 626 megabytes.

This message is the moment where abstract metadata about circuit sizes collides with physical reality. It is the pivot point between reading configuration files and touching actual hardware resources. The 626 MB figure becomes a concrete anchor for understanding the memory footprint of SnapDeals (sector update) proofs, and the near-empty listing for WindowPoSt and WinningPoSt parameters forces a re-examination of how those proof types actually work. This article unpacks the reasoning, context, assumptions, and knowledge created by this single message.

Context: The Investigation So Far

The broader investigation had been mapping the full call chain of the SUPRASEAL_C2 Groth16 proof pipeline, from Curio's Go task layer through Rust FFI into C++/CUDA kernels, with a focus on understanding the ~200 GiB peak memory footprint. The assistant had already explored several dimensions:

The Message: Bridging Metadata and Physical Reality

The message reads:

Now let me look at the actual parameter file sizes to understand circuit sizes. Let me also check for the actual .params file sizes on disk:

>

`` [bash] ls -lh /var/tmp/filecoin-proof-parameters/ 2>/dev/null | grep -E "(spacetime|sector-update)" | head -30 -rw-r--r-- 1 theuser theuser 1.4K Feb 15 19:24 v28-empty-sector-update-merkletree-poseidon_hasher-8-0-0-61fa69f38b9cc771ba27b670124714b4ea77fbeae05e377fb859c4a43b73a30c.vk -rw-r--r-- 1 theuser theuser 1.4K Feb 15 19:24 v28-empty-sector-update-merkletree-poseidon_hasher-8-0-0-92180959e1918d26350b8e6cfe217bbdd0a2d8de51ebec269078b364b715ad63.vk -rw-r--r-- 1 theuser theuser 626M Feb 15 19:25 v28-empty-sector-update-merkletree-poseidon_hasher-8-0-0-fb9e095bebdd77511c0269b967b4d87ba8b8a525edaa0e165de2... ``

The output is truncated — the full filename for the 626 MB file extends beyond the display width, indicated by the trailing "...". But the critical information is clear: the SnapDeals .params file for what appears to be a small-sector variant (the 8-0-0 in the name indicates the arity configuration, likely for 512 MiB sectors based on earlier JSON exploration) occupies 626 megabytes on disk. The two .vk (verification key) files are negligible at 1.4 KB each.

Why This Message Matters: The Reasoning and Motivation

The assistant's motivation is straightforward but important: to ground the investigation in measurable quantities. Up to this point, the assistant had been working with JSON metadata — sector sizes expressed as integers (536870912 for 512 MiB, 34359738368 for 32 GiB), CID strings, and parameter names. But the JSON only tells you what should exist, not what does exist on a real deployment. By checking /var/tmp/filecoin-proof-parameters/ — the standard cache directory for downloaded proof parameters — the assistant can:

  1. Verify which parameter files are actually present on a running Curio node, revealing which proof types have been exercised.
  2. Measure actual file sizes rather than relying on JSON declarations, which may be inaccurate or may not reflect compression.
  3. Detect anomalies — the absence of WindowPoSt/WinningPoSt .params files is the most significant finding here. The deeper reasoning is about understanding circuit complexity. In Groth16 proving systems, the .params file contains the proving key, which includes the structured reference string (SRS) and other circuit-specific data. The size of this file is directly proportional to the number of constraints in the circuit and the size of the underlying elliptic curve group. A 626 MB proving key implies a circuit with hundreds of millions of constraints — a data point that feeds directly into memory accounting and optimization proposals.

Assumptions and Their Validity

The assistant makes several assumptions in this message, most of which are reasonable but worth examining:

Assumption 1: The parameter cache directory contains the relevant files. The path /var/tmp/filecoin-proof-parameters/ is the standard location used by paramfetch and related tools. The 2>/dev/null redirection suggests the assistant is prepared for the directory not to exist, which is a prudent hedge. In this case, the directory exists and contains files, validating the assumption.

Assumption 2: Grepping for "spacetime" and "sector-update" captures all relevant proof type parameters. This is a reasonable heuristic, but it could miss parameters with different naming conventions. The earlier JSON exploration ([msg 34]) showed that all .params files in the manifest contained "empty-sector-update" in their names, so the grep for "sector-update" would catch those. The "spacetime" grep would catch WindowPoSt/WinningPoSt parameters if they existed. The empty result for "spacetime" is itself a finding.

Assumption 3: The file sizes on disk reflect the memory needed during proving. This is partially true but incomplete. The proving key must be loaded into GPU memory (or system memory for CPU proving), but the peak memory during proving also includes witness vectors, intermediate computation buffers, and the SRS. The 626 MB file is just one component of the total memory footprint.

Assumption 4: The truncated filename is unimportant. The assistant uses head -30 and accepts the truncated output. The full filename contains the hash that uniquely identifies the parameter set, but for size analysis, the truncation is harmless.

What the Message Does Not Say: The Missing Pieces

The most striking absence in the output is any file matching "spacetime." The grep pattern (spacetime|sector-update) should match both WindowPoSt/WinningPoSt parameters (which contain "proof-of-spacetime-fallback" in their names) and SnapDeals parameters (which contain "empty-sector-update"). Only the latter appear. This confirms the assistant's earlier suspicion that WindowPoSt and WinningPoSt use a fundamentally different proving mechanism — likely the "fallback" proof that doesn't require a large proving key file.

But the message does not explore why these files are missing. The assistant could have checked whether the files simply hadn't been downloaded yet (perhaps the node hadn't processed any WindowPoSt tasks), or whether the proof-of-spacetime-fallback mechanism genuinely doesn't require .params files. The subsequent messages ([msg 37]–[msg 38]) pivot to examining resource requirements in task definitions, suggesting the assistant recognized the need for a different approach to understand PoSt memory requirements.

Input Knowledge Required

To fully understand this message, a reader needs:

  1. Knowledge of the Filecoin proof parameter system: That .params files contain proving keys (including SRS), .vk files contain verification keys, and these are downloaded via paramfetch based on a JSON manifest.
  2. Understanding of Groth16 proving: That the proving key size correlates with circuit size, and that different proof types (PoRep, WindowPoSt, WinningPoSt, SnapDeals) have vastly different circuit complexities.
  3. Familiarity with the Curio codebase: That /var/tmp/filecoin-proof-parameters/ is the standard cache directory, and that the naming convention encodes proof type, hasher, arity, and sector size.
  4. Context from the preceding investigation: That the assistant had been systematically searching for WindowPoSt/WinningPoSt .params files in the JSON manifest and coming up empty.

Output Knowledge Created

This message produces several concrete pieces of knowledge:

  1. SnapDeals .params files are ~626 MB for small-sector variants. This is a lower bound on the proving key size for SnapDeals proofs. For 32 GiB and 64 GiB sectors, the files would be proportionally larger (the 8-8-0 and 8-8-2 variants seen in earlier JSON exploration).
  2. WindowPoSt and WinningPoSt .params files are absent from this deployment. This strongly suggests these proof types do not use traditional Groth16 proving keys, or they use a different parameter loading mechanism. This is consistent with the "proof-of-spacetime-fallback" naming — a simpler, non-SNARK-based proof that doesn't require large parameters.
  3. Verification keys for SnapDeals are tiny (1.4 KB). This is expected — verification keys in Groth16 are always small (just a few group elements), regardless of circuit size.
  4. The parameter cache contains only SnapDeals-related files. This implies the node has been performing SnapDeals updates but may not have exercised WindowPoSt or WinningPoSt proving on this particular machine (or those proof types use a different cache mechanism).

The Thinking Process Visible in the Message

The assistant's reasoning is visible in the structure of the command and the choice of what to examine. The phrase "Now let me look at the actual parameter file sizes to understand circuit sizes" reveals a chain of inference:

  1. Circuit size → proving key size → .params file size
  2. The JSON metadata tells us sector sizes and parameter names, but not actual file sizes
  3. Actual file sizes on disk are the ground truth
  4. Therefore, examine the parameter cache directory The choice of ls -lh with human-readable sizes (-h) and a grep filter for the two proof type families shows deliberate scoping. The assistant is not dumping the entire directory (which might contain SRS files, old parameters, or unrelated artifacts) but focusing on the specific parameter types under investigation. The 2>/dev/null suppression of stderr is a defensive programming habit — if the directory doesn't exist, the error message is noise, not signal. The head -30 limits output in case there are many files, though in practice only three match.

Impact on the Broader Investigation

This message feeds directly into the optimization proposals that the investigation would later produce. The 626 MB proving key size, combined with the knowledge that SnapDeals proofs require loading this key into GPU memory, contributes to the understanding of the ~200 GiB peak memory footprint. The absence of WindowPoSt/WinningPoSt .params files reinforces the architectural insight that these proof types use a fundamentally different (and less memory-intensive) mechanism — which in turn shapes the design of the proposed cuzk proving daemon, where different proof types would have different resource profiles and scheduling priorities.

The message also demonstrates a methodological principle: when metadata is ambiguous, go to the physical layer. The JSON manifest listed parameters for all proof types, but only by checking the actual filesystem could the assistant discover the asymmetry between SnapDeals (which had large .params files) and PoSt (which did not). This principle would serve the investigation well in subsequent phases, where actual GPU memory measurements and kernel execution times would ground the theoretical analysis.

Conclusion

Message [msg 36] is a small but pivotal step in a larger investigative journey. It is the moment when the investigation transitions from reading configuration files to measuring physical resources. The 626 MB .params file and the conspicuously absent PoSt parameters become fixed points in the mental model of the proof pipeline. For a reader coming to this investigation fresh, this message illustrates the importance of verification — of not trusting metadata alone, but reaching down to the filesystem, running the command, and seeing what is actually there. In a domain where memory footprints are measured in hundreds of gigabytes and optimization gains are measured in percentage points, such ground-truth checks are not pedantic; they are essential.