The 33 GiB Clue: How a Simple File Listing Unlocked the cuzk Phase 2 Pipeline

In the middle of implementing Phase 2 of the cuzk proving engine — a pipelined SNARK prover for Filecoin's Groth16 proofs — the assistant paused its code generation to run a seemingly trivial command: listing the size of a parameter file on disk. That single command, embedded within a message of only two sentences and a bash invocation, reveals a critical moment of discovery that shaped the architecture of the entire SRS (Structured Reference String) manager module. The message, indexed as <msg id=445>, reads in full:

The 57G one is WindowPoSt, the 184M is WinningPoSt. Now let me look at the SnapDeals: ``bash ls -lh /data/zk/params/v28-empty-sector-update-merkletree-poseidon_hasher-8-8-0-*.params ` Output: -rw-r--r-- 1 theuser theuser 33G Feb 17 16:05 /data/zk/params/v28-empty-sector-update-merkletree-poseidon_hasher-8-8-0-3b7f44a9362e3985369454947bc94022e118211e49fd672d52bec1cbfd599d18.params`

This is not merely a file lookup. It is the culmination of a deliberate reconnaissance phase, and the data it produces becomes a foundational input for the SRS manager's circuit-to-parameter mapping, memory budget calculations, and preload/evict policy. To understand why this message matters, we must trace the reasoning that led to it and the decisions it enabled.

The Context: Replacing a Monolithic Prover

The cuzk project, spanning multiple segments of development, aims to replace the monolithic Filecoin proof generation pipeline with a continuously running daemon that keeps SRS parameters resident in GPU memory across proof jobs. Phase 0 and Phase 1 ([msg 431] through [msg 438]) established the basic daemon infrastructure: a gRPC API, a multi-GPU worker pool with priority scheduling, and wrappers for all four Filecoin proof types (PoRep C2, WinningPoSt, WindowPoSt, SnapDeals). But the fundamental bottleneck remained: each proof call loaded SRS parameters from disk into GPU memory, then discarded them after proving completed. This incurred a massive I/O and initialization cost — the 57 GiB WindowPoSt parameters alone took tens of seconds to load.

Phase 2, as documented in cuzk-phase2-design.md, proposes a solution: split the monolithic proof generation into two stages — CPU circuit synthesis and GPU NTT+MSM proving — and pipeline them so the GPU never sits idle. The prerequisite was a minimal bellperson fork exposing the synthesis/GPU split point, which was completed in the previous segment ([msg 434]). Now, the assistant faced Steps 3 through 7: implementing the SRS manager, the pipeline module, and refactoring the engine.

Why This Message Was Written

The SRS manager (Step 3) must map logical circuit identifiers — CircuitId values representing PoRep C2, WinningPoSt, WindowPoSt, and SnapDeals — to physical .params files on disk. Unlike the monolithic prover, which relied on the private GROTH_PARAM_MEMORY_CACHE inside filecoin-proofs-api, the new pipeline loads parameters directly via SuprasealParameters from the bellperson fork. This means the SRS manager must know, with byte-level precision, which files exist, their sizes, and their naming conventions.

In the preceding messages ([msg 442] through [msg 444]), the assistant had already discovered the PoRep C2 param filename (v28-stacked-proof-of-replication-merkletree-poseidon_hasher-8-0-0-sha256_hasher-032d3138...) and the two PoSt variants (57 GiB and 184 MiB). But the SnapDeals circuit — which uses the "empty-sector-update" proving scheme — remained unexamined. The assistant's question "Now let me look at the SnapDeals" is not idle curiosity; it is a systematic gap-filling operation. The SRS manager cannot be written until all four circuit types have their parameter files identified.

The Thinking Process Visible in the Message

The message reveals several layers of reasoning compressed into a single line of inference. First, the assistant states "The 57G one is WindowPoSt, the 184M is WinningPoSt." This is an inference, not a fact read from any configuration file. The assistant had previously listed two .params files for proof-of-spacetime-fallback — one at 57 GiB and one at 184 MiB — but the filenames themselves did not distinguish between winning and window variants. The assistant deduced the mapping from domain knowledge: WinningPoSt proves a single sector's proof-of-spacetime and is computationally lightweight, while WindowPoSt must prove an entire window's worth of sectors and is correspondingly massive. The 57 GiB file must be WindowPoSt; the 184 MiB file must be WinningPoSt.

This is a heuristic, and it is worth noting as a potential source of error. If the assistant's assumption were wrong — if, for example, the 57 GiB file were actually a combined parameter set used for both PoSt types — the SRS manager would map circuit IDs to incorrect filenames, causing proof failures at runtime. However, the assistant's domain knowledge is sound: the Filecoin specification defines different proving parameters for winning and window PoSt, and the size disparity aligns with the computational complexity of each.

Second, the assistant selects the correct glob pattern for SnapDeals: v28-empty-sector-update-merkletree-poseidon_hasher-8-8-0-*.params. The "empty-sector-update" naming corresponds to the SnapDeals circuit, which proves that a previously empty sector has been correctly updated with new data. The 8-8-0 suffix indicates the sector size configuration (8 MiB tree, 8 MiB leaf, 0 layers of caching), which differs from PoRep's 8-0-0-sha256_hasher pattern. The assistant's ability to construct this glob pattern without referencing documentation demonstrates a deep familiarity with the Filecoin parameter naming scheme.

Input Knowledge Required

To understand this message, one must possess several layers of contextual knowledge. First, the Filecoin proof taxonomy: PoRep (Proof-of-Replication) for sector sealing, WinningPoSt for leader election, WindowPoSt for ongoing sector maintenance, and SnapDeals for sector updates. Second, the parameter file naming convention: v28-<circuit-name>-<merkle-hash>-<tree-arity>-<leaf-arity>-<caching-layers>-<hash>.params, where the hash is a content-based identifier. Third, the directory layout: /data/zk/params/ is the standard location for Filecoin proving parameters, populated by lotus fetch-params. Fourth, the relationship between circuit complexity and file size: larger parameter files correspond to circuits with more constraints, which in turn correspond to more computationally expensive proofs.

Output Knowledge Created

This message produces three concrete pieces of knowledge that flow directly into the SRS manager implementation. First, the SnapDeals parameter file is exactly 33 GiB — a critical input for the memory budget tracker, which must ensure that loading SnapDeals parameters does not exceed available GPU memory. Second, the exact filename hash (3b7f44a9362e3985369454947bc94022e118211e49fd672d52bec1cbfd599d18) is needed to construct the CircuitId-to-path mapping in srs_manager.rs. Third, the naming pattern empty-sector-update-...-8-8-0 confirms that SnapDeals uses a different tree configuration than PoRep (which uses 8-0-0-sha256_hasher), meaning the SRS manager must handle heterogeneous parameter configurations.

The Broader Significance

This message exemplifies a pattern that recurs throughout the cuzk development: the assistant alternates between high-level architectural design and low-level empirical verification. Before writing a single line of the SRS manager, it verifies the exact byte counts of every parameter file on disk. This "measure before you build" discipline prevents subtle bugs that would only surface at runtime — such as attempting to load a 57 GiB parameter set into a GPU with only 40 GiB of available memory, or constructing a filename with the wrong hash.

The 33 GiB SnapDeals parameter file also has architectural implications. Combined with the 57 GiB WindowPoSt parameters and the 184 MiB WinningPoSt parameters, the SRS manager must handle a 300:1 size disparity between the smallest and largest parameter sets. This drives the design of the preload/evict policy: WinningPoSt parameters can be permanently resident, while WindowPoSt and SnapDeals parameters may need to be loaded on demand and evicted when the memory budget is exceeded.

In the subsequent implementation ([msg 446] and beyond), the assistant will use these exact filenames to construct the CircuitId enum and the SrsManager::ensure_loaded() method. The 33 GiB figure will appear in memory budget calculations. The glob pattern will be embedded in the parameter discovery logic. What looks like a simple ls command is, in fact, the final piece of a reconnaissance puzzle that unlocks the entire Phase 2 pipeline architecture.