Add block cache tracer. (#5410)

Summary:
This PR adds a help class block cache tracer to read/write block cache accesses. It uses the trace reader/writer to perform this task.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5410

Differential Revision: D15612843

Pulled By: HaoyuHuang

fbshipit-source-id: f30fd1e1524355ca87db5d533a5c086728b141ea

CMakeLists.txt

@@ -628,6 +628,7 @@ set(SOURCES
         tools/sst_dump_tool.cc
         tools/trace_analyzer_tool.cc
         trace_replay/trace_replay.cc
+        trace_replay/block_cache_tracer.cc
         util/bloom.cc
         util/coding.cc
         util/compaction_job_stats_impl.cc

Makefile

@@ -561,6 +561,7 @@ TESTS = \
 	range_del_aggregator_test \
 	sst_file_reader_test \
 	db_secondary_test \
+	block_cache_tracer_test \
 
 PARALLEL_TEST = \
 	backupable_db_test \
@@ -1588,6 +1589,9 @@ sst_file_reader_test: table/sst_file_reader_test.o $(LIBOBJECTS) $(TESTHARNESS)
 db_secondary_test: db/db_impl/db_secondary_test.o db/db_test_util.o $(LIBOBJECTS) $(TESTHARNESS)
 	$(AM_LINK)
 
+block_cache_tracer_test: trace_replay/block_cache_tracer_test.o trace_replay/block_cache_tracer.o $(LIBOBJECTS) $(TESTHARNESS)
+	$(AM_LINK)
+
 #-------------------------------------------------
 # make install related stuff
 INSTALL_PATH ?= /usr/local

src.mk

@@ -143,6 +143,7 @@ LIB_SOURCES =                                                   \
   test_util/transaction_test_util.cc                            \
   tools/dump/db_dump_tool.cc                                    \
   trace_replay/trace_replay.cc                                  \
+  trace_replay/block_cache_tracer.cc                            \
   util/bloom.cc                                                 \
   util/build_version.cc                                         \
   util/coding.cc                                                \
@@ -371,6 +372,7 @@ MAIN_SOURCES =                                                          \
   tools/reduce_levels_test.cc                                           \
   tools/sst_dump_test.cc                                                \
   tools/trace_analyzer_test.cc						\
+  trace_replay/block_cache_tracer_test.cc                               \
   util/autovector_test.cc                                               \
   util/bloom_test.cc                                                    \
   util/coding_test.cc                                                   \

trace_replay/block_cache_tracer.cc

@@ -0,0 +1,218 @@
+//  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).
+
+#include "trace_replay/block_cache_tracer.h"
+
+#include "db/db_impl/db_impl.h"
+#include "rocksdb/slice.h"
+#include "util/coding.h"
+#include "util/hash.h"
+#include "util/string_util.h"
+
+namespace rocksdb {
+
+namespace {
+const unsigned int kCharSize = 1;
+bool ShouldTraceReferencedKey(const BlockCacheTraceRecord& record) {
+  return (record.block_type == TraceType::kBlockTraceDataBlock) &&
+         (record.caller == BlockCacheLookupCaller::kUserGet ||
+          record.caller == BlockCacheLookupCaller::kUserMGet);
+}
+}  // namespace
+
+BlockCacheTraceWriter::BlockCacheTraceWriter(
+    Env* env, const TraceOptions& trace_options,
+    std::unique_ptr<TraceWriter>&& trace_writer)
+    : env_(env),
+      trace_options_(trace_options),
+      trace_writer_(std::move(trace_writer)) {}
+
+bool BlockCacheTraceWriter::ShouldTrace(
+    const BlockCacheTraceRecord& record) const {
+  if (trace_options_.sampling_frequency == 0 ||
+      trace_options_.sampling_frequency == 1) {
+    return true;
+  }
+  // We use spatial downsampling so that we have a complete access history for a
+  // block.
+  const uint64_t hash = GetSliceNPHash64(Slice(record.block_key));
+  return hash % trace_options_.sampling_frequency == 0;
+}
+
+Status BlockCacheTraceWriter::WriteBlockAccess(
+    const BlockCacheTraceRecord& record) {
+  uint64_t trace_file_size = trace_writer_->GetFileSize();
+  if (trace_file_size > trace_options_.max_trace_file_size ||
+      !ShouldTrace(record)) {
+    return Status::OK();
+  }
+  Trace trace;
+  trace.ts = record.access_timestamp;
+  trace.type = record.block_type;
+  PutLengthPrefixedSlice(&trace.payload, record.block_key);
+  PutFixed64(&trace.payload, record.block_size);
+  PutFixed32(&trace.payload, record.cf_id);
+  PutLengthPrefixedSlice(&trace.payload, record.cf_name);
+  PutFixed32(&trace.payload, record.level);
+  PutFixed32(&trace.payload, record.sst_fd_number);
+  trace.payload.push_back(record.caller);
+  trace.payload.push_back(record.is_cache_hit);
+  trace.payload.push_back(record.no_insert);
+  if (ShouldTraceReferencedKey(record)) {
+    PutLengthPrefixedSlice(&trace.payload, record.referenced_key);
+    PutFixed64(&trace.payload, record.num_keys_in_block);
+    trace.payload.push_back(record.is_referenced_key_exist_in_block);
+  }
+  std::string encoded_trace;
+  TracerHelper::EncodeTrace(trace, &encoded_trace);
+  InstrumentedMutexLock lock_guard(&trace_writer_mutex_);
+  return trace_writer_->Write(encoded_trace);
+}
+
+Status BlockCacheTraceWriter::WriteHeader() {
+  Trace trace;
+  trace.ts = env_->NowMicros();
+  trace.type = TraceType::kTraceBegin;
+  PutLengthPrefixedSlice(&trace.payload, kTraceMagic);
+  PutFixed32(&trace.payload, kMajorVersion);
+  PutFixed32(&trace.payload, kMinorVersion);
+  std::string encoded_trace;
+  TracerHelper::EncodeTrace(trace, &encoded_trace);
+  InstrumentedMutexLock lock_guard(&trace_writer_mutex_);
+  return trace_writer_->Write(encoded_trace);
+}
+
+BlockCacheTraceReader::BlockCacheTraceReader(
+    std::unique_ptr<TraceReader>&& reader)
+    : trace_reader_(std::move(reader)) {}
+
+Status BlockCacheTraceReader::ReadHeader(BlockCacheTraceHeader* header) {
+  assert(header != nullptr);
+  std::string encoded_trace;
+  Status s = trace_reader_->Read(&encoded_trace);
+  if (!s.ok()) {
+    return s;
+  }
+  Trace trace;
+  s = TracerHelper::DecodeTrace(encoded_trace, &trace);
+  if (!s.ok()) {
+    return s;
+  }
+  header->start_time = trace.ts;
+  Slice enc_slice = Slice(trace.payload);
+  Slice magnic_number;
+  if (!GetLengthPrefixedSlice(&enc_slice, &magnic_number)) {
+    return Status::Corruption(
+        "Corrupted header in the trace file: Failed to read the magic number.");
+  }
+  if (magnic_number.ToString() != kTraceMagic) {
+    return Status::Corruption(
+        "Corrupted header in the trace file: Magic number does not match.");
+  }
+  if (!GetFixed32(&enc_slice, &header->rocksdb_major_version)) {
+    return Status::Corruption(
+        "Corrupted header in the trace file: Failed to read rocksdb major "
+        "version number.");
+  }
+  if (!GetFixed32(&enc_slice, &header->rocksdb_minor_version)) {
+    return Status::Corruption(
+        "Corrupted header in the trace file: Failed to read rocksdb minor "
+        "version number.");
+  }
+  // We should have retrieved all information in the header.
+  if (!enc_slice.empty()) {
+    return Status::Corruption(
+        "Corrupted header in the trace file: The length of header is too "
+        "long.");
+  }
+  return Status::OK();
+}
+
+Status BlockCacheTraceReader::ReadAccess(BlockCacheTraceRecord* record) {
+  assert(record);
+  std::string encoded_trace;
+  Status s = trace_reader_->Read(&encoded_trace);
+  if (!s.ok()) {
+    return s;
+  }
+  Trace trace;
+  s = TracerHelper::DecodeTrace(encoded_trace, &trace);
+  if (!s.ok()) {
+    return s;
+  }
+  record->access_timestamp = trace.ts;
+  record->block_type = trace.type;
+  Slice enc_slice = Slice(trace.payload);
+  Slice block_key;
+  if (!GetLengthPrefixedSlice(&enc_slice, &block_key)) {
+    return Status::Incomplete(
+        "Incomplete access record: Failed to read block key.");
+  }
+  record->block_key = block_key.ToString();
+  if (!GetFixed64(&enc_slice, &record->block_size)) {
+    return Status::Incomplete(
+        "Incomplete access record: Failed to read block size.");
+  }
+  if (!GetFixed32(&enc_slice, &record->cf_id)) {
+    return Status::Incomplete(
+        "Incomplete access record: Failed to read column family ID.");
+  }
+  Slice cf_name;
+  if (!GetLengthPrefixedSlice(&enc_slice, &cf_name)) {
+    return Status::Incomplete(
+        "Incomplete access record: Failed to read column family name.");
+  }
+  record->cf_name = cf_name.ToString();
+  if (!GetFixed32(&enc_slice, &record->level)) {
+    return Status::Incomplete(
+        "Incomplete access record: Failed to read level.");
+  }
+  if (!GetFixed32(&enc_slice, &record->sst_fd_number)) {
+    return Status::Incomplete(
+        "Incomplete access record: Failed to read SST file number.");
+  }
+  if (enc_slice.empty()) {
+    return Status::Incomplete(
+        "Incomplete access record: Failed to read caller.");
+  }
+  record->caller = static_cast<BlockCacheLookupCaller>(enc_slice[0]);
+  enc_slice.remove_prefix(kCharSize);
+  if (enc_slice.empty()) {
+    return Status::Incomplete(
+        "Incomplete access record: Failed to read is_cache_hit.");
+  }
+  record->is_cache_hit = static_cast<Boolean>(enc_slice[0]);
+  enc_slice.remove_prefix(kCharSize);
+  if (enc_slice.empty()) {
+    return Status::Incomplete(
+        "Incomplete access record: Failed to read no_insert.");
+  }
+  record->no_insert = static_cast<Boolean>(enc_slice[0]);
+  enc_slice.remove_prefix(kCharSize);
+
+  if (ShouldTraceReferencedKey(*record)) {
+    Slice referenced_key;
+    if (!GetLengthPrefixedSlice(&enc_slice, &referenced_key)) {
+      return Status::Incomplete(
+          "Incomplete access record: Failed to read the referenced key.");
+    }
+    record->referenced_key = referenced_key.ToString();
+    if (!GetFixed64(&enc_slice, &record->num_keys_in_block)) {
+      return Status::Incomplete(
+          "Incomplete access record: Failed to read the number of keys in the "
+          "block.");
+    }
+    if (enc_slice.empty()) {
+      return Status::Incomplete(
+          "Incomplete access record: Failed to read "
+          "is_referenced_key_exist_in_block.");
+    }
+    record->is_referenced_key_exist_in_block =
+        static_cast<Boolean>(enc_slice[0]);
+  }
+  return Status::OK();
+}
+
+}  // namespace rocksdb

trace_replay/block_cache_tracer.h

@@ -0,0 +1,105 @@
+//  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
+
+#include "monitoring/instrumented_mutex.h"
+#include "rocksdb/env.h"
+#include "rocksdb/options.h"
+#include "rocksdb/trace_reader_writer.h"
+#include "trace_replay/trace_replay.h"
+
+namespace rocksdb {
+
+enum BlockCacheLookupCaller : char {
+  kUserGet = 1,
+  kUserMGet = 2,
+  kUserIterator = 3,
+  kPrefetch = 4,
+  kCompaction = 5,
+  // All callers should be added before kMaxBlockCacheLookupCaller.
+  kMaxBlockCacheLookupCaller
+};
+
+enum Boolean : char { kTrue = 1, kFalse = 0 };
+
+struct BlockCacheTraceRecord {
+  // Required fields for all accesses.
+  uint64_t access_timestamp;
+  std::string block_key;
+  TraceType block_type;
+  uint64_t block_size;
+  uint32_t cf_id;
+  std::string cf_name;
+  uint32_t level;
+  uint32_t sst_fd_number;
+  BlockCacheLookupCaller caller;
+  Boolean is_cache_hit;
+  Boolean no_insert;
+
+  // Required fields for data block and user Get/Multi-Get only.
+  std::string referenced_key;
+  uint64_t num_keys_in_block = 0;
+  Boolean is_referenced_key_exist_in_block = Boolean::kFalse;
+};
+
+struct BlockCacheTraceHeader {
+  uint64_t start_time;
+  uint32_t rocksdb_major_version;
+  uint32_t rocksdb_minor_version;
+};
+
+// BlockCacheTraceWriter captures all RocksDB block cache accesses using a
+// user-provided TraceWriter. Every RocksDB operation is written as a single
+// trace. Each trace will have a timestamp and type, followed by the trace
+// payload.
+class BlockCacheTraceWriter {
+ public:
+  BlockCacheTraceWriter(Env* env, const TraceOptions& trace_options,
+                        std::unique_ptr<TraceWriter>&& trace_writer);
+  ~BlockCacheTraceWriter() = default;
+  // No copy and move.
+  BlockCacheTraceWriter(const BlockCacheTraceWriter&) = delete;
+  BlockCacheTraceWriter& operator=(const BlockCacheTraceWriter&) = delete;
+  BlockCacheTraceWriter(BlockCacheTraceWriter&&) = delete;
+  BlockCacheTraceWriter& operator=(BlockCacheTraceWriter&&) = delete;
+
+  Status WriteBlockAccess(const BlockCacheTraceRecord& record);
+
+  // Write a trace header at the beginning, typically on initiating a trace,
+  // with some metadata like a magic number and RocksDB version.
+  Status WriteHeader();
+
+ private:
+  bool ShouldTrace(const BlockCacheTraceRecord& record) const;
+
+  Env* env_;
+  TraceOptions trace_options_;
+  std::unique_ptr<TraceWriter> trace_writer_;
+  /*Mutex to protect trace_writer_ */
+  InstrumentedMutex trace_writer_mutex_;
+};
+
+// BlockCacheTraceReader helps read the trace file generated by
+// BlockCacheTraceWriter using a user provided TraceReader.
+class BlockCacheTraceReader {
+ public:
+  BlockCacheTraceReader(std::unique_ptr<TraceReader>&& reader);
+  ~BlockCacheTraceReader() = default;
+  // No copy and move.
+  BlockCacheTraceReader(const BlockCacheTraceReader&) = delete;
+  BlockCacheTraceReader& operator=(const BlockCacheTraceReader&) = delete;
+  BlockCacheTraceReader(BlockCacheTraceReader&&) = delete;
+  BlockCacheTraceReader& operator=(BlockCacheTraceReader&&) = delete;
+
+  Status ReadHeader(BlockCacheTraceHeader* header);
+
+  Status ReadAccess(BlockCacheTraceRecord* record);
+
+ private:
+  std::unique_ptr<TraceReader> trace_reader_;
+};
+
+}  // namespace rocksdb

trace_replay/block_cache_tracer_test.cc

@@ -0,0 +1,167 @@
+//  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).
+
+#include "trace_replay/block_cache_tracer.h"
+#include "rocksdb/env.h"
+#include "rocksdb/status.h"
+#include "rocksdb/trace_reader_writer.h"
+#include "test_util/testharness.h"
+#include "test_util/testutil.h"
+
+namespace rocksdb {
+
+namespace {
+const uint64_t kBlockSize = 1024;
+const std::string kBlockKeyPrefix = "test-block-";
+const uint32_t kCFId = 0;
+const uint32_t kLevel = 1;
+const uint64_t kSSTFDNumber = 100;
+const std::string kRefKeyPrefix = "test-get-";
+const uint64_t kNumKeysInBlock = 1024;
+}  // namespace
+
+class BlockCacheTracerTest : public testing::Test {
+ public:
+  BlockCacheTracerTest() {
+    test_path_ = test::PerThreadDBPath("block_cache_tracer_test");
+    env_ = rocksdb::Env::Default();
+    EXPECT_OK(env_->CreateDir(test_path_));
+    trace_file_path_ = test_path_ + "/block_cache_trace";
+  }
+
+  ~BlockCacheTracerTest() override {
+    EXPECT_OK(env_->DeleteFile(trace_file_path_));
+    EXPECT_OK(env_->DeleteDir(test_path_));
+  }
+
+  BlockCacheLookupCaller GetCaller(uint32_t key_id) {
+    uint32_t n = key_id % 5;
+    switch (n) {
+      case 0:
+        return BlockCacheLookupCaller::kPrefetch;
+      case 1:
+        return BlockCacheLookupCaller::kCompaction;
+      case 2:
+        return BlockCacheLookupCaller::kUserGet;
+      case 3:
+        return BlockCacheLookupCaller::kUserMGet;
+      case 4:
+        return BlockCacheLookupCaller::kUserIterator;
+    }
+    assert(false);
+  }
+
+  void WriteBlockAccess(BlockCacheTraceWriter* writer, uint32_t from_key_id,
+                        TraceType block_type, uint32_t nblocks) {
+    assert(writer);
+    for (uint32_t i = 0; i < nblocks; i++) {
+      uint32_t key_id = from_key_id + i;
+      BlockCacheTraceRecord record;
+      record.block_type = block_type;
+      record.block_size = kBlockSize + key_id;
+      record.block_key = kBlockKeyPrefix + std::to_string(key_id);
+      record.access_timestamp = env_->NowMicros();
+      record.cf_id = kCFId;
+      record.cf_name = kDefaultColumnFamilyName;
+      record.caller = GetCaller(key_id);
+      record.level = kLevel;
+      record.sst_fd_number = kSSTFDNumber + key_id;
+      record.is_cache_hit = Boolean::kFalse;
+      record.no_insert = Boolean::kFalse;
+      // Provide these fields for all block types.
+      // The writer should only write these fields for data blocks and the
+      // caller is either GET or MGET.
+      record.referenced_key = kRefKeyPrefix + std::to_string(key_id);
+      record.is_referenced_key_exist_in_block = Boolean::kTrue;
+      record.num_keys_in_block = kNumKeysInBlock;
+      ASSERT_OK(writer->WriteBlockAccess(record));
+    }
+  }
+
+  void VerifyAccess(BlockCacheTraceReader* reader, uint32_t from_key_id,
+                    TraceType block_type, uint32_t nblocks) {
+    assert(reader);
+    for (uint32_t i = 0; i < nblocks; i++) {
+      uint32_t key_id = from_key_id + i;
+      BlockCacheTraceRecord record;
+      ASSERT_OK(reader->ReadAccess(&record));
+      ASSERT_EQ(block_type, record.block_type);
+      ASSERT_EQ(kBlockSize + key_id, record.block_size);
+      ASSERT_EQ(kBlockKeyPrefix + std::to_string(key_id), record.block_key);
+      ASSERT_EQ(kCFId, record.cf_id);
+      ASSERT_EQ(kDefaultColumnFamilyName, record.cf_name);
+      ASSERT_EQ(GetCaller(key_id), record.caller);
+      ASSERT_EQ(kLevel, record.level);
+      ASSERT_EQ(kSSTFDNumber + key_id, record.sst_fd_number);
+      ASSERT_EQ(Boolean::kFalse, record.is_cache_hit);
+      ASSERT_EQ(Boolean::kFalse, record.no_insert);
+      if (block_type == TraceType::kBlockTraceDataBlock &&
+          (record.caller == BlockCacheLookupCaller::kUserGet ||
+           record.caller == BlockCacheLookupCaller::kUserMGet)) {
+        ASSERT_EQ(kRefKeyPrefix + std::to_string(key_id),
+                  record.referenced_key);
+        ASSERT_EQ(Boolean::kTrue, record.is_referenced_key_exist_in_block);
+        ASSERT_EQ(kNumKeysInBlock, record.num_keys_in_block);
+        continue;
+      }
+      ASSERT_EQ("", record.referenced_key);
+      ASSERT_EQ(Boolean::kFalse, record.is_referenced_key_exist_in_block);
+      ASSERT_EQ(0, record.num_keys_in_block);
+    }
+  }
+
+  Env* env_;
+  EnvOptions env_options_;
+  std::string trace_file_path_;
+  std::string test_path_;
+};
+
+TEST_F(BlockCacheTracerTest, MixedBlocks) {
+  {
+    // Generate a trace file containing a mix of blocks.
+    TraceOptions trace_opt;
+    std::unique_ptr<TraceWriter> trace_writer;
+    ASSERT_OK(NewFileTraceWriter(env_, env_options_, trace_file_path_,
+                                 &trace_writer));
+    BlockCacheTraceWriter writer(env_, trace_opt, std::move(trace_writer));
+    ASSERT_OK(writer.WriteHeader());
+    // Write blocks of different types.
+    WriteBlockAccess(&writer, 0, TraceType::kBlockTraceUncompressionDictBlock,
+                     10);
+    WriteBlockAccess(&writer, 10, TraceType::kBlockTraceDataBlock, 10);
+    WriteBlockAccess(&writer, 20, TraceType::kBlockTraceFilterBlock, 10);
+    WriteBlockAccess(&writer, 30, TraceType::kBlockTraceIndexBlock, 10);
+    WriteBlockAccess(&writer, 40, TraceType::kBlockTraceRangeDeletionBlock, 10);
+    ASSERT_OK(env_->FileExists(trace_file_path_));
+  }
+
+  {
+    // Verify trace file is generated correctly.
+    std::unique_ptr<TraceReader> trace_reader;
+    ASSERT_OK(NewFileTraceReader(env_, env_options_, trace_file_path_,
+                                 &trace_reader));
+    BlockCacheTraceReader reader(std::move(trace_reader));
+    BlockCacheTraceHeader header;
+    ASSERT_OK(reader.ReadHeader(&header));
+    ASSERT_EQ(kMajorVersion, header.rocksdb_major_version);
+    ASSERT_EQ(kMinorVersion, header.rocksdb_minor_version);
+    // Read blocks.
+    VerifyAccess(&reader, 0, TraceType::kBlockTraceUncompressionDictBlock, 10);
+    VerifyAccess(&reader, 10, TraceType::kBlockTraceDataBlock, 10);
+    VerifyAccess(&reader, 20, TraceType::kBlockTraceFilterBlock, 10);
+    VerifyAccess(&reader, 30, TraceType::kBlockTraceIndexBlock, 10);
+    VerifyAccess(&reader, 40, TraceType::kBlockTraceRangeDeletionBlock, 10);
+    // Read one more record should report an error.
+    BlockCacheTraceRecord record;
+    ASSERT_NOK(reader.ReadAccess(&record));
+  }
+}
+
+}  // namespace rocksdb
+
+int main(int argc, char** argv) {
+  ::testing::InitGoogleTest(&argc, argv);
+  return RUN_ALL_TESTS();
+}

trace_replay/trace_replay.cc

@@ -8,7 +8,6 @@
 #include <chrono>
 #include <sstream>
 #include <thread>
-
 #include "db/db_impl/db_impl.h"
 #include "rocksdb/slice.h"
 #include "rocksdb/write_batch.h"
@@ -32,6 +31,30 @@ void DecodeCFAndKey(std::string& buffer, uint32_t* cf_id, Slice* key) {
 }
 }  // namespace
 
+void TracerHelper::EncodeTrace(const Trace& trace, std::string* encoded_trace) {
+  assert(encoded_trace);
+  PutFixed64(encoded_trace, trace.ts);
+  encoded_trace->push_back(trace.type);
+  PutFixed32(encoded_trace, static_cast<uint32_t>(trace.payload.size()));
+  encoded_trace->append(trace.payload);
+}
+
+Status TracerHelper::DecodeTrace(const std::string& encoded_trace,
+                                 Trace* trace) {
+  assert(trace != nullptr);
+  Slice enc_slice = Slice(encoded_trace);
+  if (!GetFixed64(&enc_slice, &trace->ts)) {
+    return Status::Incomplete("Decode trace string failed");
+  }
+  if (enc_slice.size() < kTraceTypeSize + kTracePayloadLengthSize) {
+    return Status::Incomplete("Decode trace string failed");
+  }
+  trace->type = static_cast<TraceType>(enc_slice[0]);
+  enc_slice.remove_prefix(kTraceTypeSize + kTracePayloadLengthSize);
+  trace->payload = enc_slice.ToString();
+  return Status::OK();
+}
+
 Tracer::Tracer(Env* env, const TraceOptions& trace_options,
                std::unique_ptr<TraceWriter>&& trace_writer)
     : env_(env),
@@ -139,10 +162,7 @@ Status Tracer::WriteFooter() {
 
 Status Tracer::WriteTrace(const Trace& trace) {
   std::string encoded_trace;
-  PutFixed64(&encoded_trace, trace.ts);
+  TracerHelper::EncodeTrace(trace, &encoded_trace);
-  encoded_trace.push_back(trace.type);
-  PutFixed32(&encoded_trace, static_cast<uint32_t>(trace.payload.size()));
-  encoded_trace.append(trace.payload);
   return trace_writer_->Write(Slice(encoded_trace));
 }
 
@@ -302,13 +322,7 @@ Status Replayer::ReadTrace(Trace* trace) {
   if (!s.ok()) {
     return s;
   }
-
+  return TracerHelper::DecodeTrace(encoded_trace, trace);
-  Slice enc_slice = Slice(encoded_trace);
-  GetFixed64(&enc_slice, &trace->ts);
-  trace->type = static_cast<TraceType>(enc_slice[0]);
-  enc_slice.remove_prefix(kTraceTypeSize + kTracePayloadLengthSize);
-  trace->payload = enc_slice.ToString();
-  return s;
 }
 
 }  // namespace rocksdb

trace_replay/trace_replay.h

@@ -40,6 +40,12 @@ enum TraceType : char {
   kTraceGet = 4,
   kTraceIteratorSeek = 5,
   kTraceIteratorSeekForPrev = 6,
+  // Block cache related types.
+  kBlockTraceIndexBlock = 7,
+  kBlockTraceFilterBlock = 8,
+  kBlockTraceDataBlock = 9,
+  kBlockTraceUncompressionDictBlock = 10,
+  kBlockTraceRangeDeletionBlock = 11,
   // All trace types should be added before kTraceMax
   kTraceMax,
 };
@@ -60,6 +66,15 @@ struct Trace {
   }
 };
 
+class TracerHelper {
+ public:
+  // Encode a trace object into the given string.
+  static void EncodeTrace(const Trace& trace, std::string* encoded_trace);
+
+  // Decode a string into the given trace object.
+  static Status DecodeTrace(const std::string& encoded_trace, Trace* trace);
+};
+
 // Tracer captures all RocksDB operations using a user-provided TraceWriter.
 // Every RocksDB operation is written as a single trace. Each trace will have a
 // timestamp and type, followed by the trace payload.