Add statistics for BlobDB GC (#6296)

Summary:
The patch adds statistics support to the new BlobDB garbage collection implementation;
namely, it adds support for the following (pre-existing) tickers:

`BLOB_DB_GC_NUM_FILES`: the number of blob files obsoleted by the GC logic.
`BLOB_DB_GC_NUM_NEW_FILES`: the number of new blob files generated by the GC logic.
`BLOB_DB_GC_FAILURES`: the number of failed GC passes (where a GC pass is
equivalent to a (sub)compaction).
`BLOB_DB_GC_NUM_KEYS_RELOCATED`: the number of blobs relocated to new blob
files by the GC logic.
`BLOB_DB_GC_BYTES_RELOCATED`: the total size of blobs relocated to new blob files.

The tickers `BLOB_DB_GC_NUM_KEYS_OVERWRITTEN`, `BLOB_DB_GC_NUM_KEYS_EXPIRED`,
`BLOB_DB_GC_BYTES_OVERWRITTEN`, `BLOB_DB_GC_BYTES_EXPIRED`, and
`BLOB_DB_GC_MICROS` are not relevant for the new GC logic, and are thus marked
deprecated.

The patch also adds a couple of log messages that log the number and total size of
blobs encountered and relocated during a GC pass, as well as the number of blob
files created and obsoleted.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6296

Test Plan: Extended unit tests and used the BlobDB mode of `db_bench`.

Differential Revision: D19402513

Pulled By: ltamasi

fbshipit-source-id: d53d2bfbf4928a1db1e9346c67ebb9007b8932ec

HISTORY.md

@@ -4,6 +4,9 @@
 * Fix incorrect results while block-based table uses kHashSearch, together with Prev()/SeekForPrev().
 * Fix a bug that prevents opening a DB after two consecutive crash with TransactionDB, where the first crash recovers from a corrupted WAL with kPointInTimeRecovery but the second cannot.
 
+### Public API Change
+* The BlobDB garbage collector now emits the statistics `BLOB_DB_GC_NUM_FILES` (number of blob files obsoleted during GC), `BLOB_DB_GC_NUM_NEW_FILES` (number of new blob files generated during GC), `BLOB_DB_GC_FAILURES` (number of failed GC passes), `BLOB_DB_GC_NUM_KEYS_RELOCATED` (number of blobs relocated during GC), and `BLOB_DB_GC_BYTES_RELOCATED` (total size of blobs relocated during GC). On the other hand, the following statistics, which are not relevant for the new GC implementation, are now deprecated: `BLOB_DB_GC_NUM_KEYS_OVERWRITTEN`, `BLOB_DB_GC_NUM_KEYS_EXPIRED`, `BLOB_DB_GC_BYTES_OVERWRITTEN`, `BLOB_DB_GC_BYTES_EXPIRED`, and `BLOB_DB_GC_MICROS`.
+
 ## 6.7.0 (01/21/2020)
 ### Public API Change
 * Added a rocksdb::FileSystem class in include/rocksdb/file_system.h to encapsulate file creation/read/write operations, and an option DBOptions::file_system to allow a user to pass in an instance of rocksdb::FileSystem. If its a non-null value, this will take precendence over DBOptions::env for file operations. A new API rocksdb::FileSystem::Default() returns a platform default object. The DBOptions::env option and Env::Default() API will continue to be used for threading and other OS related functions, and where DBOptions::file_system is not specified, for file operations. For storage developers who are accustomed to rocksdb::Env, the interface in rocksdb::FileSystem is new and will probably undergo some changes as more storage systems are ported to it from rocksdb::Env. As of now, no env other than Posix has been ported to the new interface.

include/rocksdb/statistics.h

@@ -287,23 +287,25 @@ enum Tickers : uint32_t {
   // size of blob index evicted from base DB by BlobDB compaction filter
   // because of corresponding file deleted.
   BLOB_DB_BLOB_INDEX_EVICTED_SIZE,
-  // # of blob files being garbage collected.
+  // # of blob files that were obsoleted by garbage collection.
   BLOB_DB_GC_NUM_FILES,
   // # of blob files generated by garbage collection.
   BLOB_DB_GC_NUM_NEW_FILES,
   // # of BlobDB garbage collection failures.
   BLOB_DB_GC_FAILURES,
-  // # of keys drop by BlobDB garbage collection because they had been
-  // overwritten.
+  // # of keys dropped by BlobDB garbage collection because they had been
+  // overwritten. DEPRECATED.
   BLOB_DB_GC_NUM_KEYS_OVERWRITTEN,
-  // # of keys drop by BlobDB garbage collection because of expiration.
+  // # of keys dropped by BlobDB garbage collection because of expiration.
+  // DEPRECATED.
   BLOB_DB_GC_NUM_KEYS_EXPIRED,
   // # of keys relocated to new blob file by garbage collection.
   BLOB_DB_GC_NUM_KEYS_RELOCATED,
-  // # of bytes drop by BlobDB garbage collection because they had been
-  // overwritten.
+  // # of bytes dropped by BlobDB garbage collection because they had been
+  // overwritten. DEPRECATED.
   BLOB_DB_GC_BYTES_OVERWRITTEN,
-  // # of bytes drop by BlobDB garbage collection because of expiration.
+  // # of bytes dropped by BlobDB garbage collection because of expiration.
+  // DEPRECATED.
   BLOB_DB_GC_BYTES_EXPIRED,
   // # of bytes relocated to new blob file by garbage collection.
   BLOB_DB_GC_BYTES_RELOCATED,
@@ -420,7 +422,7 @@ enum Histograms : uint32_t {
   BLOB_DB_BLOB_FILE_READ_MICROS,
   // Blob file sync latency.
   BLOB_DB_BLOB_FILE_SYNC_MICROS,
-  // BlobDB garbage collection time.
+  // BlobDB garbage collection time. DEPRECATED.
   BLOB_DB_GC_MICROS,
   // BlobDB compression time.
   BLOB_DB_COMPRESSION_MICROS,

utilities/blob_db/blob_compaction_filter.cc

@@ -8,6 +8,8 @@
 #include "utilities/blob_db/blob_compaction_filter.h"
 #include "db/dbformat.h"
 
+#include <cinttypes>
+
 namespace rocksdb {
 namespace blob_db {
 
@@ -54,6 +56,30 @@ CompactionFilter::Decision BlobIndexCompactionFilterBase::FilterV2(
   return Decision::kKeep;
 }
 
+BlobIndexCompactionFilterGC::~BlobIndexCompactionFilterGC() {
+  if (blob_file_) {
+    CloseAndRegisterNewBlobFile();
+  }
+
+  assert(context_gc_.blob_db_impl);
+
+  ROCKS_LOG_INFO(context_gc_.blob_db_impl->db_options_.info_log,
+                 "GC pass finished %s: encountered %" PRIu64 " blobs (%" PRIu64
+                 " bytes), relocated %" PRIu64 " blobs (%" PRIu64
+                 " bytes), created %" PRIu64 " new blob file(s)",
+                 !gc_stats_.HasError() ? "successfully" : "with failure",
+                 gc_stats_.AllBlobs(), gc_stats_.AllBytes(),
+                 gc_stats_.RelocatedBlobs(), gc_stats_.RelocatedBytes(),
+                 gc_stats_.NewFiles());
+
+  RecordTick(statistics(), BLOB_DB_GC_NUM_KEYS_RELOCATED,
+             gc_stats_.RelocatedBlobs());
+  RecordTick(statistics(), BLOB_DB_GC_BYTES_RELOCATED,
+             gc_stats_.RelocatedBytes());
+  RecordTick(statistics(), BLOB_DB_GC_NUM_NEW_FILES, gc_stats_.NewFiles());
+  RecordTick(statistics(), BLOB_DB_GC_FAILURES, gc_stats_.HasError());
+}
+
 CompactionFilter::BlobDecision BlobIndexCompactionFilterGC::PrepareBlobOutput(
     const Slice& key, const Slice& existing_value,
     std::string* new_value) const {
@@ -68,13 +94,18 @@ CompactionFilter::BlobDecision BlobIndexCompactionFilterGC::PrepareBlobOutput(
   BlobIndex blob_index;
   const Status s = blob_index.DecodeFrom(existing_value);
   if (!s.ok()) {
+    gc_stats_.SetError();
     return BlobDecision::kCorruption;
   }
 
   if (blob_index.IsInlined()) {
+    gc_stats_.AddBlob(blob_index.value().size());
+
     return BlobDecision::kKeep;
   }
 
+  gc_stats_.AddBlob(blob_index.size());
+
   if (blob_index.HasTTL()) {
     return BlobDecision::kKeep;
   }
@@ -88,28 +119,34 @@ CompactionFilter::BlobDecision BlobIndexCompactionFilterGC::PrepareBlobOutput(
   // is bounded though (determined by the number of compactions and the blob
   // file size option).
   if (!OpenNewBlobFileIfNeeded()) {
+    gc_stats_.SetError();
     return BlobDecision::kIOError;
   }
 
   PinnableSlice blob;
   CompressionType compression_type = kNoCompression;
   if (!ReadBlobFromOldFile(key, blob_index, &blob, &compression_type)) {
+    gc_stats_.SetError();
     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)) {
+    gc_stats_.SetError();
     return BlobDecision::kIOError;
   }
 
   if (!CloseAndRegisterNewBlobFileIfNeeded()) {
+    gc_stats_.SetError();
     return BlobDecision::kIOError;
   }
 
   BlobIndex::EncodeBlob(new_value, new_blob_file_number, new_blob_offset,
                         blob.size(), compression_type);
 
+  gc_stats_.AddRelocatedBlob(blob_index.size());
+
   return BlobDecision::kChangeValue;
 }
 
@@ -135,6 +172,8 @@ bool BlobIndexCompactionFilterGC::OpenNewBlobFileIfNeeded() const {
   assert(blob_file_);
   assert(writer_);
 
+  gc_stats_.AddNewFile();
+
   return true;
 }
 

utilities/blob_db/blob_compaction_filter.h

@@ -11,6 +11,7 @@
 #include "monitoring/statistics.h"
 #include "rocksdb/compaction_filter.h"
 #include "rocksdb/env.h"
+#include "utilities/blob_db/blob_db_gc_stats.h"
 #include "utilities/blob_db/blob_db_impl.h"
 
 namespace rocksdb {
@@ -33,10 +34,10 @@ struct BlobCompactionContextGC {
 class BlobIndexCompactionFilterBase : public CompactionFilter {
  public:
   BlobIndexCompactionFilterBase(BlobCompactionContext&& context,
-                                uint64_t current_time, Statistics* statistics)
+                                uint64_t current_time, Statistics* stats)
       : context_(std::move(context)),
         current_time_(current_time),
-        statistics_(statistics) {}
+        statistics_(stats) {}
 
   ~BlobIndexCompactionFilterBase() override {
     RecordTick(statistics_, BLOB_DB_BLOB_INDEX_EXPIRED_COUNT, expired_count_);
@@ -52,6 +53,9 @@ class BlobIndexCompactionFilterBase : public CompactionFilter {
                     const Slice& value, std::string* /*new_value*/,
                     std::string* /*skip_until*/) const override;
 
+ protected:
+  Statistics* statistics() const { return statistics_; }
+
  private:
   BlobCompactionContext context_;
   const uint64_t current_time_;
@@ -67,9 +71,9 @@ class BlobIndexCompactionFilterBase : public CompactionFilter {
 class BlobIndexCompactionFilter : public BlobIndexCompactionFilterBase {
  public:
   BlobIndexCompactionFilter(BlobCompactionContext&& context,
-                            uint64_t current_time, Statistics* statistics)
-      : BlobIndexCompactionFilterBase(std::move(context), current_time,
-                                      statistics) {}
+                            uint64_t current_time, Statistics* stats)
+      : BlobIndexCompactionFilterBase(std::move(context), current_time, stats) {
+  }
 
   const char* Name() const override { return "BlobIndexCompactionFilter"; }
 };
@@ -78,16 +82,11 @@ class BlobIndexCompactionFilterGC : public BlobIndexCompactionFilterBase {
  public:
   BlobIndexCompactionFilterGC(BlobCompactionContext&& context,
                               BlobCompactionContextGC&& context_gc,
-                              uint64_t current_time, Statistics* statistics)
-      : BlobIndexCompactionFilterBase(std::move(context), current_time,
-                                      statistics),
+                              uint64_t current_time, Statistics* stats)
+      : BlobIndexCompactionFilterBase(std::move(context), current_time, stats),
         context_gc_(std::move(context_gc)) {}
 
-  ~BlobIndexCompactionFilterGC() override {
-    if (blob_file_) {
-      CloseAndRegisterNewBlobFile();
-    }
-  }
+  ~BlobIndexCompactionFilterGC() override;
 
   const char* Name() const override { return "BlobIndexCompactionFilterGC"; }
 
@@ -109,6 +108,7 @@ class BlobIndexCompactionFilterGC : public BlobIndexCompactionFilterBase {
   BlobCompactionContextGC context_gc_;
   mutable std::shared_ptr<BlobFile> blob_file_;
   mutable std::shared_ptr<Writer> writer_;
+  mutable BlobDBGarbageCollectionStats gc_stats_;
 };
 
 // Compaction filter factory; similarly to the filters above, it comes

utilities/blob_db/blob_db_gc_stats.h

@@ -0,0 +1,52 @@
+//  Copyright (c) 2011-present, Facebook, Inc.  All rights reserved.
+//  This source code is licensed under both the GPLv2 (found in the
+//  COPYING file in the root directory) and Apache 2.0 License
+//  (found in the LICENSE.Apache file in the root directory).
+//
+#pragma once
+
+#ifndef ROCKSDB_LITE
+
+namespace rocksdb {
+
+namespace blob_db {
+
+/**
+ * Statistics related to a single garbage collection pass (i.e. a single
+ * (sub)compaction).
+ */
+class BlobDBGarbageCollectionStats {
+ public:
+  uint64_t AllBlobs() const { return all_blobs_; }
+  uint64_t AllBytes() const { return all_bytes_; }
+  uint64_t RelocatedBlobs() const { return relocated_blobs_; }
+  uint64_t RelocatedBytes() const { return relocated_bytes_; }
+  uint64_t NewFiles() const { return new_files_; }
+  bool HasError() const { return error_; }
+
+  void AddBlob(uint64_t size) {
+    ++all_blobs_;
+    all_bytes_ += size;
+  }
+
+  void AddRelocatedBlob(uint64_t size) {
+    ++relocated_blobs_;
+    relocated_bytes_ += size;
+  }
+
+  void AddNewFile() { ++new_files_; }
+
+  void SetError() { error_ = true; }
+
+ private:
+  uint64_t all_blobs_ = 0;
+  uint64_t all_bytes_ = 0;
+  uint64_t relocated_blobs_ = 0;
+  uint64_t relocated_bytes_ = 0;
+  uint64_t new_files_ = 0;
+  bool error_ = false;
+};
+
+}  // namespace blob_db
+}  // namespace rocksdb
+#endif  // ROCKSDB_LITE

utilities/blob_db/blob_db_impl.cc

@@ -540,6 +540,8 @@ void BlobDBImpl::MarkUnreferencedBlobFilesObsoleteImpl(Functor mark_if_needed) {
   // Note: we need to stop as soon as we find a blob file that has any
   // linked SSTs (or one potentially referenced by memtables).
 
+  uint64_t obsoleted_files = 0;
+
   auto it = live_imm_non_ttl_blob_files_.begin();
   while (it != live_imm_non_ttl_blob_files_.end()) {
     const auto& blob_file = it->second;
@@ -560,6 +562,15 @@ void BlobDBImpl::MarkUnreferencedBlobFilesObsoleteImpl(Functor mark_if_needed) {
     }
 
     it = live_imm_non_ttl_blob_files_.erase(it);
+
+    ++obsoleted_files;
+  }
+
+  if (obsoleted_files > 0) {
+    ROCKS_LOG_INFO(db_options_.info_log,
+                   "%" PRIu64 " blob file(s) marked obsolete by GC",
+                   obsoleted_files);
+    RecordTick(statistics_, BLOB_DB_GC_NUM_FILES, obsoleted_files);
   }
 }
 

utilities/blob_db/blob_db_test.cc

@@ -1371,6 +1371,7 @@ TEST_F(BlobDBTest, GarbageCollection) {
 
   Options options;
   options.env = mock_env_.get();
+  options.statistics = CreateDBStatistics();
 
   Open(bdb_options, options);
 
@@ -1504,6 +1505,17 @@ TEST_F(BlobDBTest, GarbageCollection) {
 
   VerifyBaseDBBlobIndex(blob_index_versions);
 
+  const Statistics *const statistics = options.statistics.get();
+  assert(statistics);
+
+  ASSERT_EQ(statistics->getTickerCount(BLOB_DB_GC_NUM_FILES), cutoff);
+  ASSERT_EQ(statistics->getTickerCount(BLOB_DB_GC_NUM_NEW_FILES), cutoff);
+  ASSERT_EQ(statistics->getTickerCount(BLOB_DB_GC_FAILURES), 0);
+  ASSERT_EQ(statistics->getTickerCount(BLOB_DB_GC_NUM_KEYS_RELOCATED),
+            cutoff * kBlobsPerFile);
+  ASSERT_EQ(statistics->getTickerCount(BLOB_DB_GC_BYTES_RELOCATED),
+            cutoff * kBlobsPerFile * kLargeValueSize);
+
   // 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.)
   {
@@ -1522,6 +1534,47 @@ TEST_F(BlobDBTest, GarbageCollection) {
   }
 }
 
+TEST_F(BlobDBTest, GarbageCollectionFailure) {
+  BlobDBOptions bdb_options;
+  bdb_options.min_blob_size = 0;
+  bdb_options.enable_garbage_collection = true;
+  bdb_options.garbage_collection_cutoff = 1.0;
+  bdb_options.disable_background_tasks = true;
+
+  Options db_options;
+  db_options.statistics = CreateDBStatistics();
+
+  Open(bdb_options, db_options);
+
+  // Write a couple of valid blobs.
+  Put("foo", "bar");
+  Put("dead", "beef");
+
+  // Write a fake blob reference into the base DB that cannot be parsed.
+  WriteBatch batch;
+  ASSERT_OK(WriteBatchInternal::PutBlobIndex(
+      &batch, blob_db_->DefaultColumnFamily()->GetID(), "key",
+      "not a valid blob index"));
+  ASSERT_OK(blob_db_->GetRootDB()->Write(WriteOptions(), &batch));
+
+  auto blob_files = blob_db_impl()->TEST_GetBlobFiles();
+  ASSERT_EQ(blob_files.size(), 1);
+  auto blob_file = blob_files[0];
+  ASSERT_OK(blob_db_impl()->TEST_CloseBlobFile(blob_file));
+
+  ASSERT_TRUE(blob_db_->CompactRange(CompactRangeOptions(), nullptr, nullptr)
+                  .IsCorruption());
+
+  const Statistics *const statistics = db_options.statistics.get();
+  assert(statistics);
+
+  ASSERT_EQ(statistics->getTickerCount(BLOB_DB_GC_NUM_FILES), 0);
+  ASSERT_EQ(statistics->getTickerCount(BLOB_DB_GC_NUM_NEW_FILES), 1);
+  ASSERT_EQ(statistics->getTickerCount(BLOB_DB_GC_FAILURES), 1);
+  ASSERT_EQ(statistics->getTickerCount(BLOB_DB_GC_NUM_KEYS_RELOCATED), 2);
+  ASSERT_EQ(statistics->getTickerCount(BLOB_DB_GC_BYTES_RELOCATED), 7);
+}
+
 // File should be evicted after expiration.
 TEST_F(BlobDBTest, EvictExpiredFile) {
   BlobDBOptions bdb_options;