Move out valid blobs from the oldest blob files during compaction (#6121)

Summary:
The patch adds logic that relocates live blobs from the oldest N non-TTL
blob files as they are encountered during compaction (assuming the BlobDB
configuration option `enable_garbage_collection` is `true`), where N is defined
as the number of immutable non-TTL blob files multiplied by the value of
a new BlobDB configuration option called `garbage_collection_cutoff`.
(The default value of this parameter is 0.25, that is, by default the valid blobs
residing in the oldest 25% of immutable non-TTL blob files are relocated.)
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6121

Test Plan: Added unit test and tested using the BlobDB mode of `db_bench`.

Differential Revision: D18785357

Pulled By: ltamasi

fbshipit-source-id: 8c21c512a18fba777ec28765c88682bb1a5e694e

db/compaction/compaction_iterator.cc

@@ -639,6 +639,22 @@ void CompactionIterator::NextFromInput() {
 }
 
 void CompactionIterator::PrepareOutput() {
+  if (valid_) {
+    if (compaction_filter_ && ikey_.type == kTypeBlobIndex) {
+      const auto blob_decision = compaction_filter_->PrepareBlobOutput(
+          user_key(), value_, &compaction_filter_value_);
+
+      if (blob_decision == CompactionFilter::BlobDecision::kCorruption) {
+        status_ = Status::Corruption(
+            "Corrupted blob reference encountered during GC");
+      } else if (blob_decision == CompactionFilter::BlobDecision::kIOError) {
+        status_ = Status::IOError("Could not relocate blob during GC");
+      } else if (blob_decision ==
+                 CompactionFilter::BlobDecision::kChangeValue) {
+        value_ = compaction_filter_value_;
+      }
+    }
+
     // Zeroing out the sequence number leads to better compression.
     // If this is the bottommost level (no files in lower levels)
     // and the earliest snapshot is larger than this seqno
@@ -651,7 +667,7 @@ void CompactionIterator::PrepareOutput() {
     // Can we do the same for levels above bottom level as long as
     // KeyNotExistsBeyondOutputLevel() return true?
     if ((compaction_ != nullptr && !compaction_->allow_ingest_behind()) &&
-      ikeyNotNeededForIncrementalSnapshot() && bottommost_level_ && valid_ &&
+        ikeyNotNeededForIncrementalSnapshot() && bottommost_level_ &&
         IN_EARLIEST_SNAPSHOT(ikey_.sequence) && ikey_.type != kTypeMerge) {
       assert(ikey_.type != kTypeDeletion && ikey_.type != kTypeSingleDeletion);
       if (ikey_.type == kTypeDeletion || ikey_.type == kTypeSingleDeletion) {
@@ -663,6 +679,7 @@ void CompactionIterator::PrepareOutput() {
       current_key_.UpdateInternalKey(0, ikey_.type);
     }
   }
+}
 
 inline SequenceNumber CompactionIterator::findEarliestVisibleSnapshot(
     SequenceNumber in, SequenceNumber* prev_snapshot) {

include/rocksdb/compaction_filter.h

@@ -45,6 +45,8 @@ class CompactionFilter {
     kRemoveAndSkipUntil,
   };
 
+  enum class BlobDecision { kKeep, kChangeValue, kCorruption, kIOError };
+
   // Context information of a compaction run
   struct Context {
     // Does this compaction run include all data files
@@ -173,6 +175,13 @@ class CompactionFilter {
     return Decision::kKeep;
   }
 
+  // Internal (BlobDB) use only. Do not override in application code.
+  virtual BlobDecision PrepareBlobOutput(const Slice& /* key */,
+                                         const Slice& /* existing_value */,
+                                         std::string* /* new_value */) const {
+    return BlobDecision::kKeep;
+  }
+
   // This function is deprecated. Snapshots will always be ignored for
   // compaction filters, because we realized that not ignoring snapshots doesn't
   // provide the gurantee we initially thought it would provide. Repeatable

utilities/blob_db/blob_compaction_filter.cc

@@ -11,32 +11,9 @@
 namespace rocksdb {
 namespace blob_db {
 
-namespace {
+CompactionFilter::Decision BlobIndexCompactionFilterBase::FilterV2(
-
+    int /*level*/, const Slice& key, ValueType value_type, const Slice& value,
-// CompactionFilter to delete expired blob index from base DB.
+    std::string* /*new_value*/, std::string* /*skip_until*/) const {
-class BlobIndexCompactionFilter : public CompactionFilter {
- public:
-  BlobIndexCompactionFilter(BlobCompactionContext context,
-                            uint64_t current_time, Statistics* statistics)
-      : context_(context),
-        current_time_(current_time),
-        statistics_(statistics) {}
-
-  ~BlobIndexCompactionFilter() override {
-    RecordTick(statistics_, BLOB_DB_BLOB_INDEX_EXPIRED_COUNT, expired_count_);
-    RecordTick(statistics_, BLOB_DB_BLOB_INDEX_EXPIRED_SIZE, expired_size_);
-    RecordTick(statistics_, BLOB_DB_BLOB_INDEX_EVICTED_COUNT, evicted_count_);
-    RecordTick(statistics_, BLOB_DB_BLOB_INDEX_EVICTED_SIZE, evicted_size_);
-  }
-
-  const char* Name() const override { return "BlobIndexCompactionFilter"; }
-
-  // Filter expired blob indexes regardless of snapshots.
-  bool IgnoreSnapshots() const override { return true; }
-
-  Decision FilterV2(int /*level*/, const Slice& key, ValueType value_type,
-                    const Slice& value, std::string* /*new_value*/,
-                    std::string* /*skip_until*/) const override {
   if (value_type != kBlobIndex) {
     return Decision::kKeep;
   }
@@ -78,35 +55,235 @@ class BlobIndexCompactionFilter : public CompactionFilter {
   return Decision::kKeep;
 }
 
- private:
+CompactionFilter::BlobDecision BlobIndexCompactionFilterGC::PrepareBlobOutput(
-  BlobCompactionContext context_;
+    const Slice& key, const Slice& existing_value,
-  const uint64_t current_time_;
+    std::string* new_value) const {
-  Statistics* statistics_;
+  assert(new_value);
-  // It is safe to not using std::atomic since the compaction filter, created
-  // from a compaction filter factroy, will not be called from multiple threads.
-  mutable uint64_t expired_count_ = 0;
-  mutable uint64_t expired_size_ = 0;
-  mutable uint64_t evicted_count_ = 0;
-  mutable uint64_t evicted_size_ = 0;
-};
 
-}  // anonymous namespace
+  const BlobDBImpl* const blob_db_impl = context_gc_.blob_db_impl;
+  (void)blob_db_impl;
+
+  assert(blob_db_impl);
+  assert(blob_db_impl->bdb_options_.enable_garbage_collection);
+
+  BlobIndex blob_index;
+  const Status s = blob_index.DecodeFrom(existing_value);
+  if (!s.ok()) {
+    return BlobDecision::kCorruption;
+  }
+
+  if (blob_index.IsInlined()) {
+    return BlobDecision::kKeep;
+  }
+
+  if (blob_index.HasTTL()) {
+    return BlobDecision::kKeep;
+  }
+
+  if (blob_index.file_number() >= context_gc_.cutoff_file_number) {
+    return BlobDecision::kKeep;
+  }
+
+  // Note: each compaction generates its own blob files, which, depending on the
+  // workload, might result in many small blob files. The total number of files
+  // is bounded though (determined by the number of compactions and the blob
+  // file size option).
+  if (!OpenNewBlobFileIfNeeded()) {
+    return BlobDecision::kIOError;
+  }
+
+  PinnableSlice blob;
+  CompressionType compression_type = kNoCompression;
+  if (!ReadBlobFromOldFile(key, blob_index, &blob, &compression_type)) {
+    return BlobDecision::kIOError;
+  }
+
+  uint64_t new_blob_file_number = 0;
+  uint64_t new_blob_offset = 0;
+  if (!WriteBlobToNewFile(key, blob, &new_blob_file_number, &new_blob_offset)) {
+    return BlobDecision::kIOError;
+  }
+
+  if (!CloseAndRegisterNewBlobFileIfNeeded()) {
+    return BlobDecision::kIOError;
+  }
+
+  BlobIndex::EncodeBlob(new_value, new_blob_file_number, new_blob_offset,
+                        blob.size(), compression_type);
+
+  return BlobDecision::kChangeValue;
+}
+
+bool BlobIndexCompactionFilterGC::OpenNewBlobFileIfNeeded() const {
+  if (blob_file_) {
+    assert(writer_);
+    return true;
+  }
+
+  BlobDBImpl* const blob_db_impl = context_gc_.blob_db_impl;
+  assert(blob_db_impl);
+
+  const Status s = blob_db_impl->CreateBlobFileAndWriter(
+      /* has_ttl */ false, ExpirationRange(), "GC", &blob_file_, &writer_);
+  if (!s.ok()) {
+    ROCKS_LOG_ERROR(blob_db_impl->db_options_.info_log,
+                    "Error opening new blob file during GC, status: %s",
+                    s.ToString().c_str());
+
+    return false;
+  }
+
+  assert(blob_file_);
+  assert(writer_);
+
+  return true;
+}
+
+bool BlobIndexCompactionFilterGC::ReadBlobFromOldFile(
+    const Slice& key, const BlobIndex& blob_index, PinnableSlice* blob,
+    CompressionType* compression_type) const {
+  BlobDBImpl* const blob_db_impl = context_gc_.blob_db_impl;
+  assert(blob_db_impl);
+
+  const Status s = blob_db_impl->GetRawBlobFromFile(
+      key, blob_index.file_number(), blob_index.offset(), blob_index.size(),
+      blob, compression_type);
+
+  if (!s.ok()) {
+    ROCKS_LOG_ERROR(blob_db_impl->db_options_.info_log,
+                    "Error reading blob during GC, key: %s (%s), status: %s",
+                    key.ToString(/* output_hex */ true).c_str(),
+                    blob_index.DebugString(/* output_hex */ true).c_str(),
+                    s.ToString().c_str());
+
+    return false;
+  }
+
+  return true;
+}
+
+bool BlobIndexCompactionFilterGC::WriteBlobToNewFile(
+    const Slice& key, const Slice& blob, uint64_t* new_blob_file_number,
+    uint64_t* new_blob_offset) const {
+  assert(new_blob_file_number);
+  assert(new_blob_offset);
+
+  assert(blob_file_);
+  *new_blob_file_number = blob_file_->BlobFileNumber();
+
+  assert(writer_);
+  uint64_t new_key_offset = 0;
+  const Status s = writer_->AddRecord(key, blob, kNoExpiration, &new_key_offset,
+                                      new_blob_offset);
+
+  if (!s.ok()) {
+    const BlobDBImpl* const blob_db_impl = context_gc_.blob_db_impl;
+    assert(blob_db_impl);
+
+    ROCKS_LOG_ERROR(
+        blob_db_impl->db_options_.info_log,
+        "Error writing blob to new file %s during GC, key: %s, status: %s",
+        blob_file_->PathName().c_str(),
+        key.ToString(/* output_hex */ true).c_str(), s.ToString().c_str());
+    return false;
+  }
+
+  const uint64_t new_size =
+      BlobLogRecord::kHeaderSize + key.size() + blob.size();
+  blob_file_->BlobRecordAdded(new_size);
+
+  BlobDBImpl* const blob_db_impl = context_gc_.blob_db_impl;
+  assert(blob_db_impl);
+
+  blob_db_impl->total_blob_size_ += new_size;
+
+  return true;
+}
+
+bool BlobIndexCompactionFilterGC::CloseAndRegisterNewBlobFileIfNeeded() const {
+  const BlobDBImpl* const blob_db_impl = context_gc_.blob_db_impl;
+  assert(blob_db_impl);
+
+  assert(blob_file_);
+  if (blob_file_->GetFileSize() < blob_db_impl->bdb_options_.blob_file_size) {
+    return true;
+  }
+
+  return CloseAndRegisterNewBlobFile();
+}
+
+bool BlobIndexCompactionFilterGC::CloseAndRegisterNewBlobFile() const {
+  BlobDBImpl* const blob_db_impl = context_gc_.blob_db_impl;
+  assert(blob_db_impl);
+  assert(blob_file_);
+
+  Status s;
+
+  {
+    WriteLock wl(&blob_db_impl->mutex_);
+
+    s = blob_db_impl->CloseBlobFile(blob_file_);
+
+    // Note: we delay registering the new blob file until it's closed to
+    // prevent FIFO eviction from processing it during the GC run.
+    blob_db_impl->RegisterBlobFile(blob_file_);
+  }
+
+  assert(blob_file_->Immutable());
+  blob_file_.reset();
+
+  if (!s.ok()) {
+    ROCKS_LOG_ERROR(blob_db_impl->db_options_.info_log,
+                    "Error closing new blob file %s during GC, status: %s",
+                    blob_file_->PathName().c_str(), s.ToString().c_str());
+
+    return false;
+  }
+
+  return true;
+}
 
 std::unique_ptr<CompactionFilter>
 BlobIndexCompactionFilterFactory::CreateCompactionFilter(
     const CompactionFilter::Context& /*context*/) {
+  assert(env());
+
   int64_t current_time = 0;
-  Status s = env_->GetCurrentTime(&current_time);
+  Status s = env()->GetCurrentTime(&current_time);
   if (!s.ok()) {
     return nullptr;
   }
   assert(current_time >= 0);
 
+  assert(blob_db_impl());
+
   BlobCompactionContext context;
-  blob_db_impl_->GetCompactionContext(&context);
+  blob_db_impl()->GetCompactionContext(&context);
 
   return std::unique_ptr<CompactionFilter>(new BlobIndexCompactionFilter(
-      context, static_cast<uint64_t>(current_time), statistics_));
+      std::move(context), current_time, statistics()));
+}
+
+std::unique_ptr<CompactionFilter>
+BlobIndexCompactionFilterFactoryGC::CreateCompactionFilter(
+    const CompactionFilter::Context& /*context*/) {
+  assert(env());
+
+  int64_t current_time = 0;
+  Status s = env()->GetCurrentTime(&current_time);
+  if (!s.ok()) {
+    return nullptr;
+  }
+  assert(current_time >= 0);
+
+  assert(blob_db_impl());
+
+  BlobCompactionContext context;
+  BlobCompactionContextGC context_gc;
+  blob_db_impl()->GetCompactionContext(&context, &context_gc);
+
+  return std::unique_ptr<CompactionFilter>(new BlobIndexCompactionFilterGC(
+      std::move(context), std::move(context_gc), current_time, statistics()));
 }
 
 }  // namespace blob_db

utilities/blob_db/blob_compaction_filter.h

@@ -17,24 +17,113 @@ namespace rocksdb {
 namespace blob_db {
 
 struct BlobCompactionContext {
-  uint64_t next_file_number;
+  uint64_t next_file_number = 0;
   std::unordered_set<uint64_t> current_blob_files;
-  SequenceNumber fifo_eviction_seq;
+  SequenceNumber fifo_eviction_seq = 0;
-  uint64_t evict_expiration_up_to;
+  uint64_t evict_expiration_up_to = 0;
 };
 
-class BlobIndexCompactionFilterFactory : public CompactionFilterFactory {
+struct BlobCompactionContextGC {
+  BlobDBImpl* blob_db_impl = nullptr;
+  uint64_t cutoff_file_number = 0;
+};
+
+// Compaction filter that deletes expired blob indexes from the base DB.
+// Comes into two varieties, one for the non-GC case and one for the GC case.
+class BlobIndexCompactionFilterBase : public CompactionFilter {
  public:
-  BlobIndexCompactionFilterFactory(BlobDBImpl* blob_db_impl, Env* env,
+  BlobIndexCompactionFilterBase(BlobCompactionContext&& context,
+                                uint64_t current_time, Statistics* statistics)
+      : context_(std::move(context)),
+        current_time_(current_time),
+        statistics_(statistics) {}
+
+  ~BlobIndexCompactionFilterBase() override {
+    RecordTick(statistics_, BLOB_DB_BLOB_INDEX_EXPIRED_COUNT, expired_count_);
+    RecordTick(statistics_, BLOB_DB_BLOB_INDEX_EXPIRED_SIZE, expired_size_);
+    RecordTick(statistics_, BLOB_DB_BLOB_INDEX_EVICTED_COUNT, evicted_count_);
+    RecordTick(statistics_, BLOB_DB_BLOB_INDEX_EVICTED_SIZE, evicted_size_);
+  }
+
+  // Filter expired blob indexes regardless of snapshots.
+  bool IgnoreSnapshots() const override { return true; }
+
+  Decision FilterV2(int /*level*/, const Slice& key, ValueType value_type,
+                    const Slice& value, std::string* /*new_value*/,
+                    std::string* /*skip_until*/) const override;
+
+ private:
+  BlobCompactionContext context_;
+  const uint64_t current_time_;
+  Statistics* statistics_;
+  // It is safe to not using std::atomic since the compaction filter, created
+  // from a compaction filter factroy, will not be called from multiple threads.
+  mutable uint64_t expired_count_ = 0;
+  mutable uint64_t expired_size_ = 0;
+  mutable uint64_t evicted_count_ = 0;
+  mutable uint64_t evicted_size_ = 0;
+};
+
+class BlobIndexCompactionFilter : public BlobIndexCompactionFilterBase {
+ public:
+  BlobIndexCompactionFilter(BlobCompactionContext&& context,
+                            uint64_t current_time, Statistics* statistics)
+      : BlobIndexCompactionFilterBase(std::move(context), current_time,
+                                      statistics) {}
+
+  const char* Name() const override { return "BlobIndexCompactionFilter"; }
+};
+
+class BlobIndexCompactionFilterGC : public BlobIndexCompactionFilterBase {
+ public:
+  BlobIndexCompactionFilterGC(BlobCompactionContext&& context,
+                              BlobCompactionContextGC&& context_gc,
+                              uint64_t current_time, Statistics* statistics)
+      : BlobIndexCompactionFilterBase(std::move(context), current_time,
+                                      statistics),
+        context_gc_(std::move(context_gc)) {}
+
+  ~BlobIndexCompactionFilterGC() override {
+    if (blob_file_) {
+      CloseAndRegisterNewBlobFile();
+    }
+  }
+
+  const char* Name() const override { return "BlobIndexCompactionFilterGC"; }
+
+  BlobDecision PrepareBlobOutput(const Slice& key, const Slice& existing_value,
+                                 std::string* new_value) const override;
+
+ private:
+  bool OpenNewBlobFileIfNeeded() const;
+  bool ReadBlobFromOldFile(const Slice& key, const BlobIndex& blob_index,
+                           PinnableSlice* blob,
+                           CompressionType* compression_type) const;
+  bool WriteBlobToNewFile(const Slice& key, const Slice& blob,
+                          uint64_t* new_blob_file_number,
+                          uint64_t* new_blob_offset) const;
+  bool CloseAndRegisterNewBlobFileIfNeeded() const;
+  bool CloseAndRegisterNewBlobFile() const;
+
+ private:
+  BlobCompactionContextGC context_gc_;
+  mutable std::shared_ptr<BlobFile> blob_file_;
+  mutable std::shared_ptr<Writer> writer_;
+};
+
+// Compaction filter factory; similarly to the filters above, it comes
+// in two flavors, one that creates filters that support GC, and one
+// that creates non-GC filters.
+class BlobIndexCompactionFilterFactoryBase : public CompactionFilterFactory {
+ public:
+  BlobIndexCompactionFilterFactoryBase(BlobDBImpl* blob_db_impl, Env* env,
                                        Statistics* statistics)
       : blob_db_impl_(blob_db_impl), env_(env), statistics_(statistics) {}
 
-  virtual const char* Name() const override {
+ protected:
-    return "BlobIndexCompactionFilterFactory";
+  BlobDBImpl* blob_db_impl() const { return blob_db_impl_; }
-  }
+  Env* env() const { return env_; }
-
+  Statistics* statistics() const { return statistics_; }
-  virtual std::unique_ptr<CompactionFilter> CreateCompactionFilter(
-      const CompactionFilter::Context& /*context*/) override;
 
  private:
   BlobDBImpl* blob_db_impl_;
@@ -42,6 +131,36 @@ class BlobIndexCompactionFilterFactory : public CompactionFilterFactory {
   Statistics* statistics_;
 };
 
+class BlobIndexCompactionFilterFactory
+    : public BlobIndexCompactionFilterFactoryBase {
+ public:
+  BlobIndexCompactionFilterFactory(BlobDBImpl* blob_db_impl, Env* env,
+                                   Statistics* statistics)
+      : BlobIndexCompactionFilterFactoryBase(blob_db_impl, env, statistics) {}
+
+  const char* Name() const override {
+    return "BlobIndexCompactionFilterFactory";
+  }
+
+  std::unique_ptr<CompactionFilter> CreateCompactionFilter(
+      const CompactionFilter::Context& /*context*/) override;
+};
+
+class BlobIndexCompactionFilterFactoryGC
+    : public BlobIndexCompactionFilterFactoryBase {
+ public:
+  BlobIndexCompactionFilterFactoryGC(BlobDBImpl* blob_db_impl, Env* env,
+                                     Statistics* statistics)
+      : BlobIndexCompactionFilterFactoryBase(blob_db_impl, env, statistics) {}
+
+  const char* Name() const override {
+    return "BlobIndexCompactionFilterFactoryGC";
+  }
+
+  std::unique_ptr<CompactionFilter> CreateCompactionFilter(
+      const CompactionFilter::Context& /*context*/) override;
+};
+
 }  // namespace blob_db
 }  // namespace rocksdb
 #endif  // ROCKSDB_LITE

utilities/blob_db/blob_db.h

@@ -68,11 +68,15 @@ struct BlobDBOptions {
   // what compression to use for Blob's
   CompressionType compression = kNoCompression;
 
-  // If enabled, blob DB periodically cleanup stale data by rewriting remaining
+  // If enabled, BlobDB cleans up stale blobs in non-TTL files during compaction
-  // live data in blob files to new files. If garbage collection is not enabled,
+  // by rewriting the remaining live blobs to new files.
-  // blob files will be cleanup based on TTL.
   bool enable_garbage_collection = false;
 
+  // The cutoff in terms of blob file age for garbage collection. Blobs in
+  // the oldest N non-TTL blob files will be rewritten when encountered during
+  // compaction, where N = garbage_collection_cutoff * number_of_non_TTL_files.
+  double garbage_collection_cutoff = 0.25;
+
   // Disable all background job. Used for test only.
   bool disable_background_tasks = false;
 

utilities/blob_db/blob_db_impl.cc

@@ -131,13 +131,22 @@ BlobDBOptions BlobDBImpl::GetBlobDBOptions() const { return bdb_options_; }
 Status BlobDBImpl::Open(std::vector<ColumnFamilyHandle*>* handles) {
   assert(handles != nullptr);
   assert(db_ == nullptr);
+
   if (blob_dir_.empty()) {
     return Status::NotSupported("No blob directory in options");
   }
+
   if (cf_options_.compaction_filter != nullptr ||
       cf_options_.compaction_filter_factory != nullptr) {
     return Status::NotSupported("Blob DB doesn't support compaction filter.");
   }
+
+  if (bdb_options_.garbage_collection_cutoff < 0.0 ||
+      bdb_options_.garbage_collection_cutoff > 1.0) {
+    return Status::InvalidArgument(
+        "Garbage collection cutoff must be in the interval [0.0, 1.0]");
+  }
+
   // BlobDB does not support Periodic Compactions. So disable periodic
   // compactions irrespective of the user set value.
   cf_options_.periodic_compaction_seconds = 0;
@@ -185,11 +194,17 @@ Status BlobDBImpl::Open(std::vector<ColumnFamilyHandle*>* handles) {
   }
 
   // Update options
-  db_options_.listeners.push_back(bdb_options_.enable_garbage_collection
+  if (bdb_options_.enable_garbage_collection) {
-                                      ? std::make_shared<BlobDBListenerGC>(this)
+    db_options_.listeners.push_back(std::make_shared<BlobDBListenerGC>(this));
-                                      : std::make_shared<BlobDBListener>(this));
+    cf_options_.compaction_filter_factory =
-  cf_options_.compaction_filter_factory.reset(
+        std::make_shared<BlobIndexCompactionFilterFactoryGC>(this, env_,
-      new BlobIndexCompactionFilterFactory(this, env_, statistics_));
+                                                             statistics_);
+  } else {
+    db_options_.listeners.push_back(std::make_shared<BlobDBListener>(this));
+    cf_options_.compaction_filter_factory =
+        std::make_shared<BlobIndexCompactionFilterFactory>(this, env_,
+                                                           statistics_);
+  }
 
   // Open base db.
   ColumnFamilyDescriptor cf_descriptor(kDefaultColumnFamilyName, cf_options_);
@@ -607,6 +622,17 @@ std::shared_ptr<BlobFile> BlobDBImpl::NewBlobFile(
   return blob_file;
 }
 
+void BlobDBImpl::RegisterBlobFile(std::shared_ptr<BlobFile> blob_file) {
+  const uint64_t blob_file_number = blob_file->BlobFileNumber();
+
+  auto it = blob_files_.lower_bound(blob_file_number);
+  assert(it == blob_files_.end() || it->first != blob_file_number);
+
+  blob_files_.insert(it,
+                     std::map<uint64_t, std::shared_ptr<BlobFile>>::value_type(
+                         blob_file_number, std::move(blob_file)));
+}
+
 Status BlobDBImpl::CreateWriterLocked(const std::shared_ptr<BlobFile>& bfile) {
   std::string fpath(bfile->PathName());
   std::unique_ptr<WritableFile> wfile;
@@ -767,8 +793,7 @@ Status BlobDBImpl::SelectBlobFile(std::shared_ptr<BlobFile>* blob_file) {
     return s;
   }
 
-  blob_files_.insert(std::map<uint64_t, std::shared_ptr<BlobFile>>::value_type(
+  RegisterBlobFile(*blob_file);
-      (*blob_file)->BlobFileNumber(), *blob_file));
   open_non_ttl_file_ = *blob_file;
 
   return s;
@@ -814,8 +839,7 @@ Status BlobDBImpl::SelectBlobFileTTL(uint64_t expiration,
     return s;
   }
 
-  blob_files_.insert(std::map<uint64_t, std::shared_ptr<BlobFile>>::value_type(
+  RegisterBlobFile(*blob_file);
-      (*blob_file)->BlobFileNumber(), *blob_file));
   open_ttl_files_.insert(*blob_file);
 
   return s;
@@ -1062,8 +1086,9 @@ Status BlobDBImpl::CompactFiles(
   return s;
 }
 
-void BlobDBImpl::GetCompactionContext(BlobCompactionContext* context) {
+void BlobDBImpl::GetCompactionContextCommon(
-  ReadLock l(&mutex_);
+    BlobCompactionContext* context) const {
+  assert(context);
 
   context->next_file_number = next_file_number_.load();
   context->current_blob_files.clear();
@@ -1074,6 +1099,33 @@ void BlobDBImpl::GetCompactionContext(BlobCompactionContext* context) {
   context->evict_expiration_up_to = evict_expiration_up_to_;
 }
 
+void BlobDBImpl::GetCompactionContext(BlobCompactionContext* context) {
+  assert(context);
+
+  ReadLock l(&mutex_);
+  GetCompactionContextCommon(context);
+}
+
+void BlobDBImpl::GetCompactionContext(BlobCompactionContext* context,
+                                      BlobCompactionContextGC* context_gc) {
+  assert(context);
+  assert(context_gc);
+
+  ReadLock l(&mutex_);
+  GetCompactionContextCommon(context);
+
+  context_gc->blob_db_impl = this;
+
+  if (!live_imm_non_ttl_blob_files_.empty()) {
+    auto it = live_imm_non_ttl_blob_files_.begin();
+    std::advance(it, bdb_options_.garbage_collection_cutoff *
+                         live_imm_non_ttl_blob_files_.size());
+    context_gc->cutoff_file_number = it != live_imm_non_ttl_blob_files_.end()
+                                         ? it->first
+                                         : std::numeric_limits<uint64_t>::max();
+  }
+}
+
 void BlobDBImpl::UpdateLiveSSTSize() {
   uint64_t live_sst_size = 0;
   bool ok = GetIntProperty(DB::Properties::kLiveSstFilesSize, &live_sst_size);
@@ -1199,11 +1251,8 @@ Status BlobDBImpl::AppendBlob(const std::shared_ptr<BlobFile>& bfile,
     return s;
   }
 
-  // increment blob count
-  bfile->blob_count_++;
-
   uint64_t size_put = headerbuf.size() + key.size() + value.size();
-  bfile->file_size_ += size_put;
+  bfile->BlobRecordAdded(size_put);
   total_blob_size_ += size_put;
 
   if (expiration == kNoExpiration) {
@@ -1573,7 +1622,10 @@ Status BlobDBImpl::CloseBlobFile(std::shared_ptr<BlobFile> bfile) {
   assert(bfile);
   assert(!bfile->Immutable());
   assert(!bfile->Obsolete());
+
+  if (bfile->HasTTL() || bfile == open_non_ttl_file_) {
     write_mutex_.AssertHeld();
+  }
 
   ROCKS_LOG_INFO(db_options_.info_log,
                  "Closing blob file %" PRIu64 ". Path: %s",

utilities/blob_db/blob_db_impl.h

@@ -44,6 +44,7 @@ struct FlushJobInfo;
 namespace blob_db {
 
 struct BlobCompactionContext;
+struct BlobCompactionContextGC;
 class BlobDBImpl;
 class BlobFile;
 
@@ -79,6 +80,7 @@ class BlobDBImpl : public BlobDB {
   friend class BlobDBIterator;
   friend class BlobDBListener;
   friend class BlobDBListenerGC;
+  friend class BlobIndexCompactionFilterGC;
 
  public:
   // deletions check period
@@ -179,7 +181,13 @@ class BlobDBImpl : public BlobDB {
 
   Status SyncBlobFiles() override;
 
+  // Common part of the two GetCompactionContext methods below.
+  // REQUIRES: read lock on mutex_
+  void GetCompactionContextCommon(BlobCompactionContext* context) const;
+
   void GetCompactionContext(BlobCompactionContext* context);
+  void GetCompactionContext(BlobCompactionContext* context,
+                            BlobCompactionContextGC* context_gc);
 
 #ifndef NDEBUG
   Status TEST_GetBlobValue(const Slice& key, const Slice& index_entry,
@@ -247,7 +255,9 @@ class BlobDBImpl : public BlobDB {
 
   // Close a file by appending a footer, and removes file from open files list.
   // REQUIRES: lock held on write_mutex_, write lock held on both the db mutex_
-  // and the blob file's mutex_.
+  // and the blob file's mutex_. If called on a blob file which is visible only
+  // to a single thread (like in the case of new files written during GC), the
+  // locks on write_mutex_ and the blob file's mutex_ can be avoided.
   Status CloseBlobFile(std::shared_ptr<BlobFile> bfile);
 
   // Close a file if its size exceeds blob_file_size
@@ -317,6 +327,10 @@ class BlobDBImpl : public BlobDB {
                                         const ExpirationRange& expiration_range,
                                         const std::string& reason);
 
+  // Register a new blob file.
+  // REQUIRES: write lock on mutex_.
+  void RegisterBlobFile(std::shared_ptr<BlobFile> blob_file);
+
   // collect all the blob log files from the blob directory
   Status GetAllBlobFiles(std::set<uint64_t>* file_numbers);
 

utilities/blob_db/blob_db_test.cc

@@ -8,8 +8,10 @@
 #include <algorithm>
 #include <chrono>
 #include <cstdlib>
+#include <iomanip>
 #include <map>
 #include <memory>
+#include <sstream>
 #include <string>
 #include <vector>
 
@@ -35,10 +37,22 @@ class BlobDBTest : public testing::Test {
  public:
   const int kMaxBlobSize = 1 << 14;
 
-  struct BlobRecord {
+  struct BlobIndexVersion {
-    std::string key;
+    BlobIndexVersion() = default;
-    std::string value;
+    BlobIndexVersion(std::string _user_key, uint64_t _file_number,
-    uint64_t expiration = 0;
+                     uint64_t _expiration, SequenceNumber _sequence,
+                     ValueType _type)
+        : user_key(std::move(_user_key)),
+          file_number(_file_number),
+          expiration(_expiration),
+          sequence(_sequence),
+          type(_type) {}
+
+    std::string user_key;
+    uint64_t file_number = kInvalidBlobFileNumber;
+    uint64_t expiration = kNoExpiration;
+    SequenceNumber sequence = 0;
+    ValueType type = kTypeValue;
   };
 
   BlobDBTest()
@@ -230,6 +244,45 @@ class BlobDBTest : public testing::Test {
     }
   }
 
+  void VerifyBaseDBBlobIndex(
+      const std::map<std::string, BlobIndexVersion> &expected_versions) {
+    const size_t kMaxKeys = 10000;
+    std::vector<KeyVersion> versions;
+    ASSERT_OK(
+        GetAllKeyVersions(blob_db_->GetRootDB(), "", "", kMaxKeys, &versions));
+    ASSERT_EQ(versions.size(), expected_versions.size());
+
+    size_t i = 0;
+    for (const auto &expected_pair : expected_versions) {
+      const BlobIndexVersion &expected_version = expected_pair.second;
+
+      ASSERT_EQ(versions[i].user_key, expected_version.user_key);
+      ASSERT_EQ(versions[i].sequence, expected_version.sequence);
+      ASSERT_EQ(versions[i].type, expected_version.type);
+      if (versions[i].type != kTypeBlobIndex) {
+        ASSERT_EQ(kInvalidBlobFileNumber, expected_version.file_number);
+        ASSERT_EQ(kNoExpiration, expected_version.expiration);
+
+        ++i;
+        continue;
+      }
+
+      BlobIndex blob_index;
+      ASSERT_OK(blob_index.DecodeFrom(versions[i].value));
+
+      const uint64_t file_number = !blob_index.IsInlined()
+                                       ? blob_index.file_number()
+                                       : kInvalidBlobFileNumber;
+      ASSERT_EQ(file_number, expected_version.file_number);
+
+      const uint64_t expiration =
+          blob_index.HasTTL() ? blob_index.expiration() : kNoExpiration;
+      ASSERT_EQ(expiration, expected_version.expiration);
+
+      ++i;
+    }
+  }
+
   void InsertBlobs() {
     WriteOptions wo;
     std::string value;
@@ -1538,6 +1591,188 @@ TEST_F(BlobDBTest, FilterForFIFOEviction) {
   VerifyDB(data_after_compact);
 }
 
+TEST_F(BlobDBTest, GarbageCollection) {
+  constexpr size_t kNumPuts = 1 << 10;
+
+  constexpr uint64_t kExpiration = 1000;
+  constexpr uint64_t kCompactTime = 500;
+
+  constexpr uint64_t kKeySize = 7;  // "key" + 4 digits
+
+  constexpr uint64_t kSmallValueSize = 1 << 6;
+  constexpr uint64_t kLargeValueSize = 1 << 8;
+  constexpr uint64_t kMinBlobSize = 1 << 7;
+  static_assert(kSmallValueSize < kMinBlobSize, "");
+  static_assert(kLargeValueSize > kMinBlobSize, "");
+
+  constexpr size_t kBlobsPerFile = 8;
+  constexpr size_t kNumBlobFiles = kNumPuts / kBlobsPerFile;
+  constexpr uint64_t kBlobFileSize =
+      BlobLogHeader::kSize +
+      (BlobLogRecord::kHeaderSize + kKeySize + kLargeValueSize) * kBlobsPerFile;
+
+  BlobDBOptions bdb_options;
+  bdb_options.min_blob_size = kMinBlobSize;
+  bdb_options.blob_file_size = kBlobFileSize;
+  bdb_options.enable_garbage_collection = true;
+  bdb_options.garbage_collection_cutoff = 0.25;
+  bdb_options.disable_background_tasks = true;
+
+  Options options;
+  options.env = mock_env_.get();
+
+  Open(bdb_options, options);
+
+  std::map<std::string, std::string> data;
+  std::map<std::string, KeyVersion> blob_value_versions;
+  std::map<std::string, BlobIndexVersion> blob_index_versions;
+
+  Random rnd(301);
+
+  // Add a bunch of large non-TTL values. These will be written to non-TTL
+  // blob files and will be subject to GC.
+  for (size_t i = 0; i < kNumPuts; ++i) {
+    std::ostringstream oss;
+    oss << "key" << std::setw(4) << std::setfill('0') << i;
+
+    const std::string key(oss.str());
+    const std::string value(
+        test::RandomHumanReadableString(&rnd, kLargeValueSize));
+    const SequenceNumber sequence = blob_db_->GetLatestSequenceNumber() + 1;
+
+    ASSERT_OK(Put(key, value));
+    ASSERT_EQ(blob_db_->GetLatestSequenceNumber(), sequence);
+
+    data[key] = value;
+    blob_value_versions[key] = KeyVersion(key, value, sequence, kTypeBlobIndex);
+    blob_index_versions[key] =
+        BlobIndexVersion(key, /* file_number */ (i >> 3) + 1, kNoExpiration,
+                         sequence, kTypeBlobIndex);
+  }
+
+  // Add some small and/or TTL values that will be ignored during GC.
+  // First, add a large TTL value will be written to its own TTL blob file.
+  {
+    const std::string key("key2000");
+    const std::string value(
+        test::RandomHumanReadableString(&rnd, kLargeValueSize));
+    const SequenceNumber sequence = blob_db_->GetLatestSequenceNumber() + 1;
+
+    ASSERT_OK(PutUntil(key, value, kExpiration));
+    ASSERT_EQ(blob_db_->GetLatestSequenceNumber(), sequence);
+
+    data[key] = value;
+    blob_value_versions[key] = KeyVersion(key, value, sequence, kTypeBlobIndex);
+    blob_index_versions[key] =
+        BlobIndexVersion(key, /* file_number */ kNumBlobFiles + 1, kExpiration,
+                         sequence, kTypeBlobIndex);
+  }
+
+  // Now add a small TTL value (which will be inlined).
+  {
+    const std::string key("key3000");
+    const std::string value(
+        test::RandomHumanReadableString(&rnd, kSmallValueSize));
+    const SequenceNumber sequence = blob_db_->GetLatestSequenceNumber() + 1;
+
+    ASSERT_OK(PutUntil(key, value, kExpiration));
+    ASSERT_EQ(blob_db_->GetLatestSequenceNumber(), sequence);
+
+    data[key] = value;
+    blob_value_versions[key] = KeyVersion(key, value, sequence, kTypeBlobIndex);
+    blob_index_versions[key] = BlobIndexVersion(
+        key, kInvalidBlobFileNumber, kExpiration, sequence, kTypeBlobIndex);
+  }
+
+  // Finally, add a small non-TTL value (which will be stored as a regular
+  // value).
+  {
+    const std::string key("key4000");
+    const std::string value(
+        test::RandomHumanReadableString(&rnd, kSmallValueSize));
+    const SequenceNumber sequence = blob_db_->GetLatestSequenceNumber() + 1;
+
+    ASSERT_OK(Put(key, value));
+    ASSERT_EQ(blob_db_->GetLatestSequenceNumber(), sequence);
+
+    data[key] = value;
+    blob_value_versions[key] = KeyVersion(key, value, sequence, kTypeValue);
+    blob_index_versions[key] = BlobIndexVersion(
+        key, kInvalidBlobFileNumber, kNoExpiration, sequence, kTypeValue);
+  }
+
+  VerifyDB(data);
+  VerifyBaseDB(blob_value_versions);
+  VerifyBaseDBBlobIndex(blob_index_versions);
+
+  // At this point, we should have 128 immutable non-TTL files with file numbers
+  // 1..128.
+  {
+    auto live_imm_files = blob_db_impl()->TEST_GetLiveImmNonTTLFiles();
+    ASSERT_EQ(live_imm_files.size(), kNumBlobFiles);
+    for (size_t i = 0; i < kNumBlobFiles; ++i) {
+      ASSERT_EQ(live_imm_files[i]->BlobFileNumber(), i + 1);
+      ASSERT_EQ(live_imm_files[i]->GetFileSize(),
+                kBlobFileSize + BlobLogFooter::kSize);
+    }
+  }
+
+  mock_env_->set_current_time(kCompactTime);
+
+  ASSERT_OK(blob_db_->CompactRange(CompactRangeOptions(),
+                                   blob_db_->DefaultColumnFamily(), nullptr,
+                                   nullptr));
+
+  // We expect the data to remain the same and the blobs from the oldest N files
+  // to be moved to new files. Sequence numbers get zeroed out during the
+  // compaction.
+  VerifyDB(data);
+
+  for (auto &pair : blob_value_versions) {
+    KeyVersion &version = pair.second;
+    version.sequence = 0;
+  }
+
+  VerifyBaseDB(blob_value_versions);
+
+  const uint64_t cutoff = static_cast<uint64_t>(
+      bdb_options.garbage_collection_cutoff * kNumBlobFiles);
+  for (auto &pair : blob_index_versions) {
+    BlobIndexVersion &version = pair.second;
+
+    version.sequence = 0;
+
+    if (version.file_number == kInvalidBlobFileNumber) {
+      continue;
+    }
+
+    if (version.file_number > cutoff) {
+      continue;
+    }
+
+    version.file_number += kNumBlobFiles + 1;
+  }
+
+  VerifyBaseDBBlobIndex(blob_index_versions);
+
+  // At this point, we should have 128 immutable non-TTL files with file numbers
+  // 33..128 and 130..161. (129 was taken by the TTL blob file.)
+  {
+    auto live_imm_files = blob_db_impl()->TEST_GetLiveImmNonTTLFiles();
+    ASSERT_EQ(live_imm_files.size(), kNumBlobFiles);
+    for (size_t i = 0; i < kNumBlobFiles; ++i) {
+      uint64_t expected_file_number = i + cutoff + 1;
+      if (expected_file_number > kNumBlobFiles) {
+        ++expected_file_number;
+      }
+
+      ASSERT_EQ(live_imm_files[i]->BlobFileNumber(), expected_file_number);
+      ASSERT_EQ(live_imm_files[i]->GetFileSize(),
+                kBlobFileSize + BlobLogFooter::kSize);
+    }
+  }
+}
+
 // File should be evicted after expiration.
 TEST_F(BlobDBTest, EvictExpiredFile) {
   BlobDBOptions bdb_options;

utilities/blob_db/blob_file.h

@@ -27,6 +27,7 @@ class BlobFile {
   friend class BlobDBImpl;
   friend struct BlobFileComparator;
   friend struct BlobFileComparatorTTL;
+  friend class BlobIndexCompactionFilterGC;
 
  private:
   // access to parent
@@ -240,6 +241,11 @@ class BlobFile {
   void SetFileSize(uint64_t fs) { file_size_ = fs; }
 
   void SetBlobCount(uint64_t bc) { blob_count_ = bc; }
+
+  void BlobRecordAdded(uint64_t record_size) {
+    ++blob_count_;
+    file_size_ += record_size;
+  }
 };
 }  // namespace blob_db
 }  // namespace rocksdb