[pbs-devel] [PATCH proxmox-backup v7 22/38] datastore: implement garbage collection for s3 backend

From: Christian Ebner <c.ebner@proxmox.com>
To: pbs-devel@lists.proxmox.com
Subject: [pbs-devel] [PATCH proxmox-backup v7 22/38] datastore: implement garbage collection for s3 backend
Date: Thu, 10 Jul 2025 19:07:12 +0200	[thread overview]
Message-ID: <20250710170728.102829-32-c.ebner@proxmox.com> (raw)
In-Reply-To: <20250710170728.102829-1-c.ebner@proxmox.com>

Implements the garbage collection for datastores backed by an s3
object store.
Take advantage of the local datastore by placing marker files in the
chunk store during phase 1 of the garbage collection, updating their
atime if already present.
This allows us to avoid making expensive API calls to update object
metadata, which would only be possible via a copy object operation.

The phase 2 is implemented by fetching a list of all the chunks via
the ListObjectsV2 API call, filtered by the chunk folder prefix.
This operation has to be performed in batches of 1000 objects, given
by the APIs response limits.
For each object key, lookup the marker file and decide based on the
marker existence and it's atime if the chunk object needs to be
removed. Deletion happens via the delete objects operation, allowing
to delete multiple chunks by a single request.

This allows to efficiently lookup chunks which are not in use
anymore while being performant and cost effective.

Baseline runtime performance tests:
-----------------------------------

3 garbage collection runs were performed with hot filesystem caches
(by additional GC run before the test runs). The PBS instance was
virtualized, the same virtualized disk using ZFS for all the local
cache stores:

All datastores contained the same encrypted data, with the following
content statistics:
Original data usage: 269.685 GiB
On-Disk usage: 9.018 GiB (3.34%)
On-Disk chunks: 6477
Deduplication factor: 29.90
Average chunk size: 1.426 MiB

The resutlts demonstrate the overhead caused by the additional
ListObjectV2 API calls and their processing, but depending on the
object store backend.

Average garbage collection runtime:
Local datastore:             (2.04 ± 0.01) s
Local RADOS gateway (Squid): (3.05 ± 0.01) s
AWS S3:                      (3.05 ± 0.01) s
Cloudflare R2:               (6.71 ± 0.58) s

After pruning of all datastore contents (therefore including
DeleteObjects requests):
Local datastore:              3.04 s
Local RADOS gateway (Squid): 14.08 s
AWS S3:                      13.06 s
Cloudflare R2:               78.21 s

Signed-off-by: Christian Ebner <c.ebner@proxmox.com>
---
changes since version 6:
- adapt commit message and add basic performance test results
- add error context to list object v2 call

 pbs-datastore/src/chunk_store.rs |   4 +
 pbs-datastore/src/datastore.rs   | 211 +++++++++++++++++++++++++++----
 2 files changed, 190 insertions(+), 25 deletions(-)

diff --git a/pbs-datastore/src/chunk_store.rs b/pbs-datastore/src/chunk_store.rs
index 8c195df54..95f00e8d5 100644
--- a/pbs-datastore/src/chunk_store.rs
+++ b/pbs-datastore/src/chunk_store.rs
@@ -353,6 +353,10 @@ impl ChunkStore {
         ProcessLocker::oldest_shared_lock(self.locker.clone().unwrap())
     }
 
+    pub fn mutex(&self) -> &std::sync::Mutex<()> {
+        &self.mutex
+    }
+
     pub fn sweep_unused_chunks(
         &self,
         oldest_writer: i64,
diff --git a/pbs-datastore/src/datastore.rs b/pbs-datastore/src/datastore.rs
index ca099c1d0..6cc7fdbaa 100644
--- a/pbs-datastore/src/datastore.rs
+++ b/pbs-datastore/src/datastore.rs
@@ -4,7 +4,7 @@ use std::os::unix::ffi::OsStrExt;
 use std::os::unix::io::AsRawFd;
 use std::path::{Path, PathBuf};
 use std::sync::{Arc, LazyLock, Mutex};
-use std::time::Duration;
+use std::time::{Duration, SystemTime};
 
 use anyhow::{bail, format_err, Context, Error};
 use http_body_util::BodyExt;
@@ -1209,6 +1209,7 @@ impl DataStore {
         chunk_lru_cache: &mut Option<LruCache<[u8; 32], ()>>,
         status: &mut GarbageCollectionStatus,
         worker: &dyn WorkerTaskContext,
+        s3_client: Option<Arc<S3Client>>,
     ) -> Result<(), Error> {
         status.index_file_count += 1;
         status.index_data_bytes += index.index_bytes();
@@ -1225,21 +1226,41 @@ impl DataStore {
                 }
             }
 
-            if !self.inner.chunk_store.cond_touch_chunk(digest, false)? {
-                let hex = hex::encode(digest);
-                warn!(
-                    "warning: unable to access non-existent chunk {hex}, required by {file_name:?}"
-                );
-
-                // touch any corresponding .bad files to keep them around, meaning if a chunk is
-                // rewritten correctly they will be removed automatically, as well as if no index
-                // file requires the chunk anymore (won't get to this loop then)
-                for i in 0..=9 {
-                    let bad_ext = format!("{}.bad", i);
-                    let mut bad_path = PathBuf::new();
-                    bad_path.push(self.chunk_path(digest).0);
-                    bad_path.set_extension(bad_ext);
-                    self.inner.chunk_store.cond_touch_path(&bad_path, false)?;
+            match s3_client {
+                None => {
+                    // Filesystem backend
+                    if !self.inner.chunk_store.cond_touch_chunk(digest, false)? {
+                        let hex = hex::encode(digest);
+                        warn!(
+                            "warning: unable to access non-existent chunk {hex}, required by {file_name:?}"
+                        );
+
+                        // touch any corresponding .bad files to keep them around, meaning if a chunk is
+                        // rewritten correctly they will be removed automatically, as well as if no index
+                        // file requires the chunk anymore (won't get to this loop then)
+                        for i in 0..=9 {
+                            let bad_ext = format!("{}.bad", i);
+                            let mut bad_path = PathBuf::new();
+                            bad_path.push(self.chunk_path(digest).0);
+                            bad_path.set_extension(bad_ext);
+                            self.inner.chunk_store.cond_touch_path(&bad_path, false)?;
+                        }
+                    }
+                }
+                Some(ref _s3_client) => {
+                    // Update atime on local cache marker files.
+                    if !self.inner.chunk_store.cond_touch_chunk(digest, false)? {
+                        let (chunk_path, _digest) = self.chunk_path(digest);
+                        // Insert empty file as marker to tell GC phase2 that this is
+                        // a chunk still in-use, so to keep in the S3 object store.
+                        std::fs::File::options()
+                            .write(true)
+                            .create_new(true)
+                            .open(&chunk_path)
+                            .with_context(|| {
+                                format!("failed to create marker for chunk {}", hex::encode(digest))
+                            })?;
+                    }
                 }
             }
         }
@@ -1251,6 +1272,7 @@ impl DataStore {
         status: &mut GarbageCollectionStatus,
         worker: &dyn WorkerTaskContext,
         cache_capacity: usize,
+        s3_client: Option<Arc<S3Client>>,
     ) -> Result<(), Error> {
         // Iterate twice over the datastore to fetch index files, even if this comes with an
         // additional runtime cost:
@@ -1344,6 +1366,7 @@ impl DataStore {
                                 &mut chunk_lru_cache,
                                 status,
                                 worker,
+                                s3_client.as_ref().cloned(),
                             )?;
 
                             if !unprocessed_index_list.remove(&path) {
@@ -1378,7 +1401,14 @@ impl DataStore {
                     continue;
                 }
             };
-            self.index_mark_used_chunks(index, &path, &mut chunk_lru_cache, status, worker)?;
+            self.index_mark_used_chunks(
+                index,
+                &path,
+                &mut chunk_lru_cache,
+                status,
+                worker,
+                s3_client.as_ref().cloned(),
+            )?;
             warn!("Marked chunks for unexpected index file at '{path:?}'");
         }
         if strange_paths_count > 0 {
@@ -1476,18 +1506,149 @@ impl DataStore {
                 1024 * 1024
             };
 
-            info!("Start GC phase1 (mark used chunks)");
+            let s3_client = match self.backend()? {
+                DatastoreBackend::Filesystem => None,
+                DatastoreBackend::S3(s3_client) => {
+                    proxmox_async::runtime::block_on(s3_client.head_bucket())
+                        .context("failed to reach bucket")?;
+                    Some(s3_client)
+                }
+            };
 
-            self.mark_used_chunks(&mut gc_status, worker, gc_cache_capacity)
-                .context("marking used chunks failed")?;
+            info!("Start GC phase1 (mark used chunks)");
 
-            info!("Start GC phase2 (sweep unused chunks)");
-            self.inner.chunk_store.sweep_unused_chunks(
-                oldest_writer,
-                min_atime,
+            self.mark_used_chunks(
                 &mut gc_status,
                 worker,
-            )?;
+                gc_cache_capacity,
+                s3_client.as_ref().cloned(),
+            )
+            .context("marking used chunks failed")?;
+
+            info!("Start GC phase2 (sweep unused chunks)");
+
+            if let Some(ref s3_client) = s3_client {
+                let mut chunk_count = 0;
+                let prefix = S3PathPrefix::Some(".chunks/".to_string());
+                // Operates in batches of 1000 objects max per request
+                let mut list_bucket_result =
+                    proxmox_async::runtime::block_on(s3_client.list_objects_v2(&prefix, None))
+                        .context("failed to list chunk in s3 object store")?;
+
+                let mut delete_list = Vec::with_capacity(1000);
+                loop {
+                    let lock = self.inner.chunk_store.mutex().lock().unwrap();
+
+                    for content in list_bucket_result.contents {
+                        // Check object is actually a chunk
+                        let digest = match Path::new::<str>(&content.key).file_name() {
+                            Some(file_name) => file_name,
+                            // should never be the case as objects will have a filename
+                            None => continue,
+                        };
+                        let bytes = digest.as_bytes();
+                        if bytes.len() != 64 && bytes.len() != 64 + ".0.bad".len() {
+                            continue;
+                        }
+                        if !bytes.iter().take(64).all(u8::is_ascii_hexdigit) {
+                            continue;
+                        }
+
+                        let bad = bytes.ends_with(b".bad");
+
+                        // Safe since contains valid ascii hexdigits only as checked above.
+                        let digest_str = digest.to_string_lossy();
+                        let hexdigit_prefix = unsafe { digest_str.get_unchecked(0..4) };
+                        let mut chunk_path = self.base_path();
+                        chunk_path.push(".chunks");
+                        chunk_path.push(hexdigit_prefix);
+                        chunk_path.push(digest);
+
+                        // Check local markers (created or atime updated during phase1) and
+                        // keep or delete chunk based on that.
+                        let atime = match std::fs::metadata(chunk_path) {
+                            Ok(stat) => stat.accessed()?,
+                            Err(err) if err.kind() == std::io::ErrorKind::NotFound => {
+                                // File not found, delete by setting atime to unix epoch
+                                info!("Not found, mark for deletion: {}", content.key);
+                                SystemTime::UNIX_EPOCH
+                            }
+                            Err(err) => return Err(err.into()),
+                        };
+                        let atime = atime.duration_since(SystemTime::UNIX_EPOCH)?.as_secs() as i64;
+
+                        chunk_count += 1;
+
+                        if atime < min_atime {
+                            delete_list.push(content.key);
+                            if bad {
+                                gc_status.removed_bad += 1;
+                            } else {
+                                gc_status.removed_chunks += 1;
+                            }
+                            gc_status.removed_bytes += content.size;
+                        } else if atime < oldest_writer {
+                            if bad {
+                                gc_status.still_bad += 1;
+                            } else {
+                                gc_status.pending_chunks += 1;
+                            }
+                            gc_status.pending_bytes += content.size;
+                        } else {
+                            if !bad {
+                                gc_status.disk_chunks += 1;
+                            }
+                            gc_status.disk_bytes += content.size;
+                        }
+                    }
+
+                    if !delete_list.is_empty() {
+                        let delete_objects_result = proxmox_async::runtime::block_on(
+                            s3_client.delete_objects(&delete_list),
+                        )?;
+                        if let Some(_err) = delete_objects_result.error {
+                            bail!("failed to delete some objects");
+                        }
+                        delete_list.clear();
+                    }
+
+                    drop(lock);
+
+                    // Process next batch of chunks if there is more
+                    if list_bucket_result.is_truncated {
+                        list_bucket_result =
+                            proxmox_async::runtime::block_on(s3_client.list_objects_v2(
+                                &prefix,
+                                list_bucket_result.next_continuation_token.as_deref(),
+                            ))?;
+                        continue;
+                    }
+
+                    break;
+                }
+                info!("processed {chunk_count} total chunks");
+
+                // Phase 2 GC of Filesystem backed storage is phase 3 for S3 backed GC
+                info!("Start GC phase3 (sweep unused chunk markers)");
+
+                let mut tmp_gc_status = GarbageCollectionStatus {
+                    upid: Some(upid.to_string()),
+                    ..Default::default()
+                };
+                self.inner.chunk_store.sweep_unused_chunks(
+                    oldest_writer,
+                    min_atime,
+                    &mut tmp_gc_status,
+                    worker,
+                )?;
+            } else {
+                self.inner.chunk_store.sweep_unused_chunks(
+                    oldest_writer,
+                    min_atime,
+                    &mut gc_status,
+                    worker,
+                )?;
+            }
 
             info!(
                 "Removed garbage: {}",
-- 
2.47.2



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