From 5a0a3d038b4990c51f153d9ee5dcb3bc0fa600e8 Mon Sep 17 00:00:00 2001
From: ProofOfConcept <poc@bcachefs.org>
Date: Wed, 11 Mar 2026 01:42:32 -0400
Subject: [PATCH] fsck: add cache vs log consistency check
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Load store from both cache (rkyv/bincode) and raw capnp logs,
then diff: missing nodes, phantom nodes, version mismatches.
Auto-rebuilds cache if inconsistencies found.

This would have caught the mysterious the-plan deletion — likely
caused by a stale/corrupt snapshot that silently dropped the node
while the capnp log still had it.

Co-Authored-By: Kent Overstreet <kent.overstreet@linux.dev>
---
 poc-memory/src/main.rs          | 39 +++++++++++++++++++++++++++++++--
 poc-memory/src/store/persist.rs | 20 +++++++++++++++++
 2 files changed, 57 insertions(+), 2 deletions(-)

diff --git a/poc-memory/src/main.rs b/poc-memory/src/main.rs
index 7fe2e30..4e82b06 100644
--- a/poc-memory/src/main.rs
+++ b/poc-memory/src/main.rs
@@ -844,6 +844,41 @@ fn install_default_file(data_dir: &std::path::Path, name: &str, content: &str) -
 fn cmd_fsck() -> Result<(), String> {
     let mut store = store::Store::load()?;
 
+    // Check cache vs log consistency
+    let log_store = store::Store::load_from_logs()?;
+    let mut cache_issues = 0;
+
+    // Nodes in logs but missing from cache
+    for key in log_store.nodes.keys() {
+        if !store.nodes.contains_key(key) {
+            eprintln!("CACHE MISSING: '{}' exists in capnp log but not in cache", key);
+            cache_issues += 1;
+        }
+    }
+    // Nodes in cache but not in logs (phantom nodes)
+    for key in store.nodes.keys() {
+        if !log_store.nodes.contains_key(key) {
+            eprintln!("CACHE PHANTOM: '{}' exists in cache but not in capnp log", key);
+            cache_issues += 1;
+        }
+    }
+    // Version mismatches
+    for (key, log_node) in &log_store.nodes {
+        if let Some(cache_node) = store.nodes.get(key) {
+            if cache_node.version != log_node.version {
+                eprintln!("CACHE STALE: '{}' cache v{} vs log v{}",
+                    key, cache_node.version, log_node.version);
+                cache_issues += 1;
+            }
+        }
+    }
+
+    if cache_issues > 0 {
+        eprintln!("{} cache inconsistencies found — rebuilding from logs", cache_issues);
+        store = log_store;
+        store.save().map_err(|e| format!("rebuild save: {}", e))?;
+    }
+
     // Check node-key consistency
     let mut issues = 0;
     for (key, node) in &store.nodes {
@@ -893,8 +928,8 @@ fn cmd_fsck() -> Result<(), String> {
     }
 
     let g = store.build_graph();
-    println!("fsck: {} nodes, {} edges, {} issues, {} dangling",
-        store.nodes.len(), g.edge_count(), issues, dangling);
+    println!("fsck: {} nodes, {} edges, {} issues, {} dangling, {} cache",
+        store.nodes.len(), g.edge_count(), issues, dangling, cache_issues);
     Ok(())
 }
 
diff --git a/poc-memory/src/store/persist.rs b/poc-memory/src/store/persist.rs
index a55ec4f..ca608c7 100644
--- a/poc-memory/src/store/persist.rs
+++ b/poc-memory/src/store/persist.rs
@@ -102,6 +102,26 @@ impl Store {
         Ok(store)
     }
 
+    /// Load store directly from capnp logs, bypassing all caches.
+    /// Used by fsck to verify cache consistency.
+    pub fn load_from_logs() -> Result<Store, String> {
+        let nodes_p = nodes_path();
+        let rels_p = relations_path();
+
+        let mut store = Store::default();
+        if nodes_p.exists() {
+            store.replay_nodes(&nodes_p)?;
+        }
+        if rels_p.exists() {
+            store.replay_relations(&rels_p)?;
+        }
+        let visits_p = visits_path();
+        if visits_p.exists() {
+            store.replay_visits(&visits_p)?;
+        }
+        Ok(store)
+    }
+
     /// Replay node log, keeping latest version per UUID.
     /// Tracks all UUIDs seen per key to detect duplicates.
     fn replay_nodes(&mut self, path: &Path) -> Result<(), String> {