Expose the amount of garbage in live blob files as a dedicated DB property

HISTORY.md

@@ -19,6 +19,7 @@
 * Add new stat ASYNC_READ_BYTES that calculates number of bytes read during async read call and users can check if async code path is being called by RocksDB internal automatic prefetching for sequential reads.
 * Enable async prefetching if ReadOptions.readahead_size is set along with ReadOptions.async_io in FilePrefetchBuffer.
 * Add event listener support on remote compaction compactor side.
+* Added a dedicated integer DB property `rocksdb.live-blob-file-garbage-size` that exposes the total amount of garbage in the blob files in the current version.
 
 ### Behavior changes
 * Disallow usage of commit-time-write-batch for write-prepared/write-unprepared transactions if TransactionOptions::use_only_the_last_commit_time_batch_for_recovery is false to prevent two (or more) uncommitted versions of the same key in the database. Otherwise, bottommost compaction may violate the internal key uniqueness invariant of SSTs if the sequence numbers of both internal keys are zeroed out (#9794).

db/blob/db_blob_basic_test.cc

@@ -733,6 +733,14 @@ TEST_F(DBBlobBasicTest, Properties) {
                                   &live_blob_file_size));
   ASSERT_EQ(live_blob_file_size, total_expected_size);
 
+  // Total amount of garbage in live blob files
+  {
+    uint64_t live_blob_file_garbage_size = 0;
+    ASSERT_TRUE(db_->GetIntProperty(DB::Properties::kLiveBlobFileGarbageSize,
+                                    &live_blob_file_garbage_size));
+    ASSERT_EQ(live_blob_file_garbage_size, 0);
+  }
+
   // Total size of all blob files across all versions
   // Note: this should be the same as above since we only have one
   // version at this point.
@@ -768,6 +776,14 @@ TEST_F(DBBlobBasicTest, Properties) {
       << "\nBlob file space amplification: " << expected_space_amp << '\n';
 
   ASSERT_EQ(blob_stats, oss.str());
+
+  // Total amount of garbage in live blob files
+  {
+    uint64_t live_blob_file_garbage_size = 0;
+    ASSERT_TRUE(db_->GetIntProperty(DB::Properties::kLiveBlobFileGarbageSize,
+                                    &live_blob_file_garbage_size));
+    ASSERT_EQ(live_blob_file_garbage_size, expected_garbage_size);
+  }
 }
 
 TEST_F(DBBlobBasicTest, PropertiesMultiVersion) {

db/internal_stats.cc

@@ -305,6 +305,8 @@ static const std::string num_blob_files = "num-blob-files";
 static const std::string blob_stats = "blob-stats";
 static const std::string total_blob_file_size = "total-blob-file-size";
 static const std::string live_blob_file_size = "live-blob-file-size";
+static const std::string live_blob_file_garbage_size =
+    "live-blob-file-garbage-size";
 
 const std::string DB::Properties::kNumFilesAtLevelPrefix =
     rocksdb_prefix + num_files_at_level_prefix;
@@ -405,6 +407,8 @@ const std::string DB::Properties::kTotalBlobFileSize =
     rocksdb_prefix + total_blob_file_size;
 const std::string DB::Properties::kLiveBlobFileSize =
     rocksdb_prefix + live_blob_file_size;
+const std::string DB::Properties::kLiveBlobFileGarbageSize =
+    rocksdb_prefix + live_blob_file_garbage_size;
 
 const UnorderedMap<std::string, DBPropertyInfo>
     InternalStats::ppt_name_to_info = {
@@ -563,6 +567,9 @@ const UnorderedMap<std::string, DBPropertyInfo>
         {DB::Properties::kLiveBlobFileSize,
          {false, nullptr, &InternalStats::HandleLiveBlobFileSize, nullptr,
           nullptr}},
+        {DB::Properties::kLiveBlobFileGarbageSize,
+         {false, nullptr, &InternalStats::HandleLiveBlobFileGarbageSize,
+          nullptr, nullptr}},
 };
 
 InternalStats::InternalStats(int num_levels, SystemClock* clock,
@@ -758,6 +765,7 @@ bool InternalStats::HandleLiveSstFilesSizeAtTemperature(std::string* value,
 
 bool InternalStats::HandleNumBlobFiles(uint64_t* value, DBImpl* /*db*/,
                                        Version* /*version*/) {
+  assert(value);
   assert(cfd_);
 
   const auto* current = cfd_->current();
@@ -774,6 +782,7 @@ bool InternalStats::HandleNumBlobFiles(uint64_t* value, DBImpl* /*db*/,
 }
 
 bool InternalStats::HandleBlobStats(std::string* value, Slice /*suffix*/) {
+  assert(value);
   assert(cfd_);
 
   const auto* current = cfd_->current();
@@ -798,6 +807,7 @@ bool InternalStats::HandleBlobStats(std::string* value, Slice /*suffix*/) {
 
 bool InternalStats::HandleTotalBlobFileSize(uint64_t* value, DBImpl* /*db*/,
                                             Version* /*version*/) {
+  assert(value);
   assert(cfd_);
 
   *value = cfd_->GetTotalBlobFileSize();
@@ -807,6 +817,7 @@ bool InternalStats::HandleTotalBlobFileSize(uint64_t* value, DBImpl* /*db*/,
 
 bool InternalStats::HandleLiveBlobFileSize(uint64_t* value, DBImpl* /*db*/,
                                            Version* /*version*/) {
+  assert(value);
   assert(cfd_);
 
   const auto* current = cfd_->current();
@@ -820,6 +831,23 @@ bool InternalStats::HandleLiveBlobFileSize(uint64_t* value, DBImpl* /*db*/,
   return true;
 }
 
+bool InternalStats::HandleLiveBlobFileGarbageSize(uint64_t* value,
+                                                  DBImpl* /*db*/,
+                                                  Version* /*version*/) {
+  assert(value);
+  assert(cfd_);
+
+  const auto* current = cfd_->current();
+  assert(current);
+
+  const auto* vstorage = current->storage_info();
+  assert(vstorage);
+
+  *value = vstorage->GetBlobStats().total_garbage_size;
+
+  return true;
+}
+
 const DBPropertyInfo* GetPropertyInfo(const Slice& property) {
   std::string ppt_name = GetPropertyNameAndArg(property).first.ToString();
   auto ppt_info_iter = InternalStats::ppt_name_to_info.find(ppt_name);

db/internal_stats.h

@@ -691,6 +691,9 @@ class InternalStats {
   bool HandleBlobStats(std::string* value, Slice suffix);
   bool HandleTotalBlobFileSize(uint64_t* value, DBImpl* db, Version* version);
   bool HandleLiveBlobFileSize(uint64_t* value, DBImpl* db, Version* version);
+  bool HandleLiveBlobFileGarbageSize(uint64_t* value, DBImpl* db,
+                                     Version* version);
+
   // Total number of background errors encountered. Every time a flush task
   // or compaction task fails, this counter is incremented. The failure can
   // be caused by any possible reason, including file system errors, out of

include/rocksdb/db.h

@@ -1060,6 +1060,10 @@ class DB {
     // "rocksdb.live-blob-file-size" - returns the total size of all blob
     //      files in the current version.
     static const std::string kLiveBlobFileSize;
+
+    // "rocksdb.live-blob-file-garbage-size" - returns the total amount of
+    // garbage in the blob files in the current version.
+    static const std::string kLiveBlobFileGarbageSize;
   };
 #endif /* ROCKSDB_LITE */