A Git Forensic Deep-Dive: Tracing Deleted Cache Code in a Distributed Storage System

Introduction

In the midst of deploying a fully functional QA test cluster for a horizontally scalable S3-compatible distributed storage system across three physical nodes, a seemingly simple question from the user triggered a meticulous forensic investigation through the project's Git history. The user asked: "Why is some gc/cache code removed in git diff??" This question, innocuous on its surface, prompted the assistant to trace a trail of uncommitted deletions back to their origin, ultimately producing a message that serves as a masterclass in systematic debugging of repository state anomalies.

The subject message—a single shell command and its truncated output—is deceptively brief. It reads:

[assistant] [bash] cd /home/theuser/gw && git show 500133f --stat | head -20 commit 500133f423cfbfdaf58fe1c531a9b0b5bead872d Author: Łukasz Magiera <[REDACTED_EMAIL]> Date: Sat Jan 31 21:14:58 2026 +0100

feat: implement multi-tier retrieval cache system (Milestone 03)

Implement persistent retrieval caches with intelligent prefetching:

L1 ARC Cache (rbcache/arc.go): - Adaptive Replacement Cache for scan-resistant memory caching - Balances recency vs frequency based on access patterns - Ghost lists (B1/B2) for adaptation without stori...

This message is the culmination of a multi-step investigation into why code that had been carefully implemented, committed, and validated across multiple milestones appeared to have vanished from the working tree. To understand its significance, we must reconstruct the reasoning chain that led to this precise moment.

The Context: A QA Cluster Under Construction

The broader session involved deploying a QA/test environment for the FGW (Filecoin Gateway) distributed storage system. The architecture consisted of three physical nodes: a head node running YugabyteDB (the distributed SQL and CQL database), and two storage nodes running the Kuri daemon. The assistant had just finished resolving a series of operational issues—dirty CQL migration states that prevented the Kuri services from starting, missing environment variable configurations, and the deployment of an S3 proxy frontend to enable cross-node object reads.

The deployment was successful. Both Kuri nodes were running, the S3 API was responding, the Web UI was accessible, and the cluster topology API showed both nodes as healthy. The assistant had provided a comprehensive deployment summary with internet port mappings and quick test commands. Everything appeared to be in order.

Then the user interjected with a question that revealed a hidden problem: "Why is some gc/cache code removed in git diff??"

The Investigation Unfolds

The assistant's response to the user's question was not a single message but a systematic investigation spanning multiple commands. The reasoning process is visible in the sequence of diagnostic steps:

Step 1: Check the committed diff. The assistant first ran git diff HEAD~5 --stat to see what had changed across the last five commits. This showed mostly additions—dashboard JSON files, Prometheus rules, Ansible playbooks—all with + signs indicating new code. The assistant specifically grepped for cache and GC related files and confirmed they were all being added, not removed.

Step 2: Check uncommitted changes. When the committed diff showed only additions, the assistant pivoted to check the working tree with git diff --stat. This revealed the problem: three files had been modified with 397 lines deleted and only 11 lines added. The files were configuration/config.go, rbdeal/claim_extender.go, and rbdeal/retr_provider.go.

Step 3: Examine the actual deletions. The assistant then inspected the diffs of each file. In configuration/config.go, entire GC configuration struct fields had been removed. In rbdeal/retr_provider.go, import statements for configuration and rbcache packages had been deleted, along with the code that used them.

Step 4: Check the commit history. The assistant ran git log --oneline -10 to understand the repository's commit structure. This revealed the key commits: Milestone 03 (500133f: "feat: implement multi-tier retrieval cache system") and Milestone 04 (39436d5: "feat: implement passive garbage collection system").

Step 5: Check for stashed changes. The assistant ran git stash list to see if the deletions had been stashed. The result was empty—no stashes existed.

Step 6: Show the original commit. This brings us to the subject message. The assistant ran git show 500133f --stat | head -20 to display the Milestone 03 commit that introduced the cache system. This was the final piece of evidence needed to establish provenance: the cache and GC code did exist in the committed history, authored by the project maintainer on a specific date with a detailed commit message describing the implementation.## The Reasoning Behind the Message

Why did the assistant run this specific command at this moment? The reasoning is a textbook example of differential diagnosis in software forensics.

The assistant had already established three facts:

The committed diff showed additions, not removals. The cache and GC code was present in the repository's committed history.
The working tree showed deletions. Three files had been modified to remove cache and GC integration code.
No stashes existed. The deletions weren't temporarily shelved. The logical conclusion was that the working tree had been modified after the commits were made, removing code that had been intentionally committed. The assistant needed to confirm that the code did exist in the committed state, ruling out the possibility that the code had never been committed or was only partially implemented. The git show 500133f --stat command served this purpose perfectly. It displayed the full commit metadata—author, date, commit message—along with a summary of all files changed in that commit. The output confirmed that Milestone 03 was a substantial implementation: rbcache/arc.go (472 lines), rbcache/arc_test.go (314 lines), rbcache/prefetcher.go (521 lines), rbcache/prefetcher_test.go (473 lines), rbcache/ssd.go (916 lines), and rbcache/ssd_test.go (additional lines). The commit message described the architecture in detail: L1 ARC Cache with Adaptive Replacement, L2 SSD Cache with SLRU eviction, access tracking with pattern detection, and DAG-aware prefetch engine. This was not a trivial addition. It was a carefully engineered multi-tier caching system with tests, spanning thousands of lines of code across multiple files. The assistant's message implicitly communicated: "This code was real, it was committed, and it was substantial. Something has gone wrong in the working tree."

Assumptions Made

The assistant made several assumptions during this investigation:

The user's observation was accurate. The assistant did not question whether the user had misread the diff. Instead, it immediately investigated, trusting that the user had seen something real.

The deletions were unintentional. The assistant's language—"This looks like the code was added in commits but then removed in the working directory"—implied an assumption that the working tree changes were accidental or erroneous, not deliberate refactoring. This was a reasonable assumption given that the user was asking "why" rather than stating an intent to remove the code.

The commit history was authoritative. The assistant treated the committed state as the ground truth and the working tree as the anomaly. This is the correct mental model for Git-based development: commits represent intentional history, while the working tree represents in-progress changes.

Mistakes and Incorrect Assumptions

The investigation was thorough, but one subtle mistake is worth noting. The assistant initially ran git diff HEAD~5 --stat and concluded "The GC and cache code is all being added (+ signs), not removed." This was technically correct for the committed diff, but it was a premature conclusion that didn't account for uncommitted changes. The assistant corrected this immediately in the next command by checking git diff --stat (which shows only uncommitted changes), but the initial framing could have led the user to believe the deletions didn't exist.

Additionally, the assistant never explicitly answered the user's "why" question. The investigation established what happened and where the code existed, but it didn't determine how the working tree became modified. The assistant checked for stashes (none found) and examined the diffs, but it didn't check git reflog, git bisect, or ask the user about their workflow. The implicit answer—"the code was committed but then removed in the working tree"—left the root cause unexplained. Was it a failed merge? An accidental git checkout of an older version? A script that modified files? The investigation stopped at diagnosis without reaching a root cause.

Input and Output Knowledge

Input knowledge required to understand this message: The reader must understand Git concepts including commits, working trees, diffs, stashes, and the distinction between committed history and uncommitted changes. Knowledge of the project structure—that rbcache/ contains the retrieval cache implementation, that configuration/config.go holds GC settings, and that rbdeal/ contains deal-related code—is necessary to interpret the significance of the deletions. Familiarity with the milestone structure (Milestone 03 = cache system, Milestone 04 = GC system) helps contextualize why the deletions were alarming.

Output knowledge created by this message: The message establishes that the multi-tier retrieval cache system (Milestone 03) was successfully committed to the repository at a specific commit hash, with a detailed commit message describing its architecture. It confirms the code's existence, authorship, and scope. For anyone reading this message later, it serves as a forensic record that the cache code was present in the repository as of commit 500133f, providing a reference point for recovery.

The Thinking Process

The thinking process visible in the assistant's reasoning is a model of systematic debugging:

Trust but verify the user's claim. The user reported deletions; the assistant checked both committed and uncommitted diffs.
Narrow the scope. Starting from a broad diff (5 commits), the assistant progressively narrowed to specific files and specific deletions.
Establish provenance. The assistant traced the code to its originating commit, confirming it was intentionally authored and committed.
Check for common Git pitfalls. The assistant checked for stashes, a common place where changes can be hidden.
Present the evidence. The final message shows the commit that introduced the code, providing irrefutable proof of its existence. This approach—start broad, narrow systematically, check common failure modes, present evidence—is applicable far beyond Git forensics. It's the same pattern used in network troubleshooting, database query optimization, and mechanical debugging.

Conclusion

The subject message, a single git show command, is the capstone of a careful forensic investigation into unexpected code deletions. It demonstrates that even in the midst of a complex multi-node deployment with live services, the assistant maintained the discipline to trace repository anomalies to their source. While the root cause of the deletions remained unexplained, the investigation successfully established the provenance of the missing code and provided a clear picture of the repository's state. For the user, this message was the evidence needed to understand that the cache and GC code was not lost—it was committed, intact, and recoverable. The message stands as a testament to the value of systematic thinking in software engineering: when something seems wrong, the first step is not to panic, but to gather evidence.