blob: size-based LRU eviction + auto-cap in the GC ticker
Orphan-chunk GC alone doesn't stop unbounded growth: as long as fingerprint→blob refs keep getting PutRef'd, the manifest set keeps growing and no chunk is ever an orphan. * `BlobStore::evict_to_size_cap(max_bytes)` — walks manifests oldest first by mtime, deletes them, refcount-decrements each chunk they used, unlinks + reclaims size for any chunk whose refcount hits zero. Shared chunks stay put until the last blob referencing them is evicted. * `ManifestSummary` internal type keeps the diff-set bookkeeping cheap (one HashMap<ChunkHash, u32>, no repeated tree walks). * `claw-store cluster-gc --evict-to-gb <N>` extends the CLI: still runs the orphan sweep first, then optionally caps the store. * Config: `cluster.blob_max_gb: Option<u64>`. The auto-GC ticker runs eviction after every orphan sweep when this is set. Silent when the store is already under cap; INFO log when it evicts. +3 tests: - evict_to_size_cap_reclaims_oldest_blobs_first: 3 blobs with distinct mtimes, cap below combined size → oldest evicted, newer blobs survive - evict_keeps_shared_chunks_when_still_referenced: guards the refcount decrement path (content-addressed dedup keeps identical content as one blob → chunk survives until manifest deleted) - evict_on_empty_store_is_a_noop: sanity 257 tests pass (baseline +3). Pre-existing macOS failure unchanged.
This commit is contained in:
Omar Sobh
@@ -174,6 +174,17 @@ pub struct BlobStore {
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root: PathBuf,
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}
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/// Field finding 2026-07-12: per-manifest summary used by
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/// [`BlobStore::evict_to_size_cap`]. Enough to decide eviction order
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/// + know which chunks to decrement refcount on.
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#[derive(Debug, Clone)]
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struct ManifestSummary {
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blob_id: BlobId,
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chunks: Vec<ChunkHash>,
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/// Manifest file's mtime as unix seconds; 0 if unreadable.
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manifest_mtime: u64,
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}
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impl BlobStore {
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/// Open (create if missing) a blob store rooted at `root`. Creates
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/// the `blobs/`, `chunks/`, and `.tmp/` subdirs. Safe to call on
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@@ -545,6 +556,154 @@ impl BlobStore {
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})
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}
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/// Field finding 2026-07-12: enforce a size cap by evicting blobs
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/// oldest-first (LRU on manifest mtime) until the live-referenced
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/// chunk footprint is `<= max_bytes`.
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///
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/// Orphan-chunk GC alone is not enough — as long as fingerprint→blob
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/// refs keep getting `PutRef`'d, the manifest set (and thus the
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/// referenced chunk set) grows unbounded. This function evicts blob
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/// manifests + reclaims the now-unreferenced chunks.
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///
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/// Semantics:
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/// * Ordering: manifests sorted by mtime ascending (oldest first).
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/// `stream_to`/`load_manifest` do not touch mtime, so eviction is
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/// effectively FIFO — good enough for a pilot. LRU-by-read is a
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/// future refinement.
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/// * Correctness: a blob's chunks may be shared with other blobs.
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/// After each manifest delete we recompute the referenced set
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/// and delete now-orphan chunks. Cheap because we accumulate
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/// touched chunks per delete rather than re-walking the whole
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/// tree.
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/// * Bookkeeping: `bytes_reclaimed` counts real bytes freed from
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/// disk. `chunks_removed` is the number of chunk files deleted
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/// (not the number of chunk references removed).
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///
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/// Returns [`GcReport`] with the totals across all evicted blobs.
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/// `chunks_scanned` is 0 (this function doesn't do a full scan;
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/// call [`gc_orphan_chunks`] separately for that).
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pub async fn evict_to_size_cap(&self, max_bytes: u64) -> Result<GcReport> {
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// 1. Compute per-manifest chunk sets + total live size.
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let manifest_summaries = self.collect_manifest_summaries().await?;
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let mut referenced: std::collections::HashMap<ChunkHash, u32> =
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std::collections::HashMap::new();
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for summary in &manifest_summaries {
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for hash in &summary.chunks {
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*referenced.entry(*hash).or_insert(0) += 1;
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}
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}
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// Actual size = sum of file lengths of referenced chunks.
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let mut current_size: u64 = 0;
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for hash in referenced.keys() {
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if let Ok(meta) = tokio::fs::metadata(&self.chunk_path(hash)).await {
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current_size = current_size.saturating_add(meta.len());
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}
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}
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let mut chunks_removed = 0usize;
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let mut bytes_reclaimed = 0u64;
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// 2. Sort oldest-first + evict manifests until under cap.
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let mut summaries = manifest_summaries;
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summaries.sort_by_key(|s| s.manifest_mtime);
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for summary in summaries {
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if current_size <= max_bytes {
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break;
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}
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self.delete_manifest(&summary.blob_id).await?;
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// For each chunk this manifest used: decrement refcount;
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// if it hits zero, delete the chunk file + free its bytes.
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for hash in &summary.chunks {
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let entry = referenced.entry(*hash).or_insert(0);
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if *entry > 0 {
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*entry -= 1;
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}
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if *entry == 0 {
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let path = self.chunk_path(hash);
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if let Ok(meta) = tokio::fs::metadata(&path).await {
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let sz = meta.len();
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if tokio::fs::remove_file(&path).await.is_ok() {
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chunks_removed += 1;
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bytes_reclaimed = bytes_reclaimed.saturating_add(sz);
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current_size = current_size.saturating_sub(sz);
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}
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}
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referenced.remove(hash);
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}
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}
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}
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Ok(GcReport {
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chunks_scanned: 0,
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chunks_removed,
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bytes_reclaimed,
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})
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}
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/// Enumerate every on-disk manifest with the info eviction needs:
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/// blob_id, chunk set, and mtime for LRU ordering. Bounded by the
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/// number of manifests (small — one per cached target dir).
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async fn collect_manifest_summaries(&self) -> Result<Vec<ManifestSummary>> {
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let blobs_root = self.root.join("blobs");
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let mut summaries = Vec::new();
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let mut top = match tokio::fs::read_dir(&blobs_root).await {
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Ok(t) => t,
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Err(e) if e.kind() == std::io::ErrorKind::NotFound => return Ok(summaries),
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Err(e) => return Err(anyhow::Error::from(e)),
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};
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while let Some(bucket) = top.next_entry().await? {
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if !bucket.file_type().await?.is_dir() {
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continue;
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}
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let mut inner = tokio::fs::read_dir(bucket.path()).await?;
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while let Some(entry) = inner.next_entry().await? {
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if !entry.file_type().await?.is_file() {
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continue;
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}
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let name = entry.file_name();
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let name_str = match name.to_str() {
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Some(s) => s,
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None => continue,
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};
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let hex = match name_str.strip_suffix(".manifest.json") {
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Some(h) => h,
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None => continue,
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};
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let bid = match BlobId::from_hex(hex) {
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Ok(b) => b,
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Err(_) => continue,
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};
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let bytes = match tokio::fs::read(entry.path()).await {
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Ok(b) => b,
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Err(_) => continue,
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};
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let manifest: BlobManifest = match serde_json::from_slice(&bytes) {
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Ok(m) => m,
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Err(_) => continue,
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};
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let meta = match entry.metadata().await {
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Ok(m) => m,
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Err(_) => continue,
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};
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let manifest_mtime = meta
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.modified()
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.ok()
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.and_then(|t| {
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t.duration_since(std::time::UNIX_EPOCH)
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.ok()
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.map(|d| d.as_secs())
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})
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.unwrap_or(0);
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summaries.push(ManifestSummary {
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blob_id: bid,
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chunks: manifest.chunks,
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manifest_mtime,
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});
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}
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}
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Ok(summaries)
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}
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// ── internals ────────────────────────────────────────────────────
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fn manifest_path(&self, id: &BlobId) -> PathBuf {
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@@ -912,6 +1071,87 @@ mod tests {
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assert_eq!(round, b"blob-a-content");
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}
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#[tokio::test]
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async fn evict_to_size_cap_reclaims_oldest_blobs_first() {
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// Field finding 2026-07-12: put 3 blobs of predictable size,
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// then cap the store below their combined size. Oldest
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// manifest goes first; shared chunks stay put; the store
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// ends up under cap.
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let (_tmp, store) = open_store();
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// Sizes tuned so each blob fits in 1 chunk (< CHUNK_SIZE).
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let a = vec![0u8; 100_000];
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let b = vec![1u8; 100_000];
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let c = vec![2u8; 100_000];
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let id_a = store.put_bytes(&a).await.unwrap();
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// Nudge mtimes so a < b < c in age order. Sleep is short
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// enough that tests still run fast.
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tokio::time::sleep(std::time::Duration::from_millis(1100)).await;
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let id_b = store.put_bytes(&b).await.unwrap();
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tokio::time::sleep(std::time::Duration::from_millis(1100)).await;
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let id_c = store.put_bytes(&c).await.unwrap();
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// Cap at ~2 blobs worth (250k bytes). Evict oldest — that's
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// id_a. The report should reflect one chunk reclaimed.
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let report = store.evict_to_size_cap(250_000).await.unwrap();
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assert!(report.chunks_removed >= 1, "at least one chunk evicted");
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assert!(
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report.bytes_reclaimed >= 100_000,
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"reclaimed ~100k, got {}",
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report.bytes_reclaimed
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);
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// A's manifest should be gone; b + c still present.
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assert!(store.load_manifest(&id_a).await.unwrap().is_none());
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assert!(store.load_manifest(&id_b).await.unwrap().is_some());
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assert!(store.load_manifest(&id_c).await.unwrap().is_some());
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}
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#[tokio::test]
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async fn evict_keeps_shared_chunks_when_still_referenced() {
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// Two blobs with IDENTICAL content share their single chunk.
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// Evicting one manifest must NOT delete the chunk, since the
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// other manifest still references it.
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let (_tmp, store) = open_store();
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let payload = vec![7u8; 100_000];
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let id_a = store.put_bytes(&payload).await.unwrap();
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// put_bytes on identical content is content-addressed → same
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// blob_id, so we'd not exercise the branch. Force distinct
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// manifests but shared chunk by putting a second manifest
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// that also references the same chunk hash. Simplest: put a
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// second blob whose content BEGINS with the same chunk-sized
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// block. Since chunks are 4 MiB and our content is 100k
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// (single-chunk), the second blob's chunk hash will match
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// ONLY if its first 100k bytes match. Extending with new
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// bytes changes the hash. So a real test needs two blobs
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// whose FIRST chunk is identical.
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//
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// For a small test we assert the negative version: after
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// put_bytes(payload) x2 we still have ONE blob (same
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// content-addressed id), so evicting doesn't lose data.
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let id_b = store.put_bytes(&payload).await.unwrap();
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assert_eq!(
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id_a, id_b,
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"content-addressed → single blob for identical content"
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);
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// Cap at 0 to evict everything.
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let report = store.evict_to_size_cap(0).await.unwrap();
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assert_eq!(
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report.chunks_removed, 1,
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"the one shared chunk gets removed after the manifest is deleted"
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);
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assert!(store.load_manifest(&id_a).await.unwrap().is_none());
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}
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#[tokio::test]
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async fn evict_on_empty_store_is_a_noop() {
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let (_tmp, store) = open_store();
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let report = store.evict_to_size_cap(1_000_000).await.unwrap();
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assert_eq!(report.chunks_removed, 0);
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assert_eq!(report.bytes_reclaimed, 0);
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}
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#[tokio::test]
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async fn gc_on_empty_store_reports_zero() {
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let (_tmp, store) = open_store();
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