lean_ctx/core/
graph_cache.rs

1//! Resident graph-index cache (Phase 5 of the efficiency epic).
2//!
3//! Materializing a `ProjectIndex` from the property graph (open SQLite + query
4//! files/symbols/edges) on *every* query that touches the graph (symbol
5//! lookups, related hints, impact) is wasteful. This keeps the materialized
6//! index resident in RAM keyed by project root, invalidated by the on-disk
7//! `graph.meta.json` fingerprint so a background rebuild is picked up
8//! immediately (no TTL wait). Callers that need an owned value get a cheap
9//! in-memory clone instead of a SQLite round-trip.
10
11use std::collections::HashMap;
12use std::sync::{Arc, Mutex, OnceLock};
13use std::time::{Instant, SystemTime};
14
15/// Max distinct project roots kept resident. A daemon touching many roots/branches/
16/// worktrees would otherwise retain every ProjectIndex (MBs each) forever. LRU-evict
17/// beyond this; an evicted root pays one materialization (SQLite query) on its next
18/// query — bounded and self-healing.
19const MAX_ROOTS: usize = 8;
20
21use crate::core::graph_index::ProjectIndex;
22
23/// `(mtime, size)` fingerprint of the on-disk graph store. Size pairs with mtime
24/// to catch same-second rebuilds that coarse (1–2 s) filesystem mtime would
25/// otherwise hide — cheap, no file read.
26#[derive(Clone, Copy, PartialEq, Eq, Default)]
27struct Fingerprint {
28    mtime: Option<SystemTime>,
29    size: u64,
30}
31
32struct Entry {
33    index: Arc<ProjectIndex>,
34    fingerprint: Fingerprint,
35    last_access: Instant,
36}
37
38static CACHE: OnceLock<Mutex<HashMap<String, Entry>>> = OnceLock::new();
39
40fn cache() -> &'static Mutex<HashMap<String, Entry>> {
41    CACHE.get_or_init(|| Mutex::new(HashMap::new()))
42}
43
44/// `(mtime, size)` of the persisted property graph, if any.
45///
46/// Since #696 C4 the property graph is the sole store; every mirror rewrites
47/// `graph.meta.json` (fresh `built_at` + node/edge counts) so its `(mtime, size)`
48/// shifts on each rebuild — a reliable, read-free invalidation signal. The
49/// `graph.db` file is the fallback when no meta has been stamped yet.
50fn index_fingerprint(project_root: &str) -> Fingerprint {
51    let Some(dir) = ProjectIndex::index_dir(project_root) else {
52        return Fingerprint::default();
53    };
54    for name in ["graph.meta.json", "graph.db"] {
55        if let Ok(meta) = std::fs::metadata(dir.join(name)) {
56            return Fingerprint {
57                mtime: meta.modified().ok(),
58                size: meta.len(),
59            };
60        }
61    }
62    Fingerprint::default()
63}
64
65/// Returns the resident `ProjectIndex` for `project_root`, loading from disk
66/// only when absent or when the on-disk index file changed. `None` when no
67/// non-empty index exists on disk.
68pub fn get_cached(project_root: &str) -> Option<Arc<ProjectIndex>> {
69    let fingerprint = index_fingerprint(project_root);
70
71    {
72        let mut map = cache()
73            .lock()
74            .unwrap_or_else(std::sync::PoisonError::into_inner);
75        if let Some(entry) = map.get_mut(project_root)
76            && entry.fingerprint == fingerprint
77        {
78            entry.last_access = Instant::now();
79            return Some(Arc::clone(&entry.index));
80        }
81    }
82
83    let idx = ProjectIndex::load(project_root).filter(|i| !i.files.is_empty())?;
84    let arc = Arc::new(idx);
85
86    let mut map = cache()
87        .lock()
88        .unwrap_or_else(std::sync::PoisonError::into_inner);
89    // LRU-evict before inserting a *new* root so the cap holds. Re-inserting an
90    // existing root (fingerprint changed) just overwrites and doesn't grow the map.
91    if !map.contains_key(project_root)
92        && map.len() >= MAX_ROOTS
93        && let Some(lru_key) = map
94            .iter()
95            .min_by_key(|(_, e)| e.last_access)
96            .map(|(k, _)| k.clone())
97    {
98        map.remove(&lru_key);
99    }
100    map.insert(
101        project_root.to_string(),
102        Entry {
103            index: Arc::clone(&arc),
104            fingerprint,
105            last_access: Instant::now(),
106        },
107    );
108    Some(arc)
109}
110
111/// Drops the cached graph index for a root (or all roots when `None`).
112pub fn invalidate(project_root: Option<&str>) {
113    let mut map = cache()
114        .lock()
115        .unwrap_or_else(std::sync::PoisonError::into_inner);
116    match project_root {
117        Some(root) => {
118            map.remove(root);
119        }
120        None => map.clear(),
121    }
122}
123
124#[cfg(test)]
125mod tests {
126    use super::*;
127
128    #[test]
129    fn returns_none_without_index() {
130        let tmp = tempfile::tempdir().unwrap();
131        invalidate(None);
132        assert!(get_cached(tmp.path().to_str().unwrap()).is_none());
133    }
134}
lean_ctx/core/graph_cache.rs

lean_ctx/core/
graph_cache.rs
