Clean up BlobLogReader and rename it to BlobLogSequentialReader (#7517)

Summary:
The patch does some cleanup in and around the legacy `BlobLogReader` class:
* It renames the class to `BlobLogSequentialReader` to emphasize that it is for
sequentially iterating through blobs in a blob file, as opposed to doing random
point reads using `BlobIndex`es (which is `BlobFileReader`'s jurisdiction).
* It removes some dead code from the old BlobDB implementation that references
`BlobLogReader` (namely the method `BlobFile::OpenRandomAccessReader`).
* It cleans up some `#include`s and forward declarations.
* It fixes some incorrect/outdated comments related to the reader class.
* It adds a few assertions to the `Read` methods of the class.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7517

Test Plan: `make check`

Reviewed By: riversand963

Differential Revision: D24172611

Pulled By: ltamasi

fbshipit-source-id: 43e2ae1eba5c3dd30c1070cb00f217edc45bd64f

CMakeLists.txt

@@ -575,7 +575,7 @@ set(SOURCES
         db/blob/blob_file_meta.cc
         db/blob/blob_file_reader.cc
         db/blob/blob_log_format.cc
-        db/blob/blob_log_reader.cc
+        db/blob/blob_log_sequential_reader.cc
         db/blob/blob_log_writer.cc
         db/builder.cc
         db/c.cc

TARGETS

@@ -139,7 +139,7 @@ cpp_library(
         "db/blob/blob_file_meta.cc",
         "db/blob/blob_file_reader.cc",
         "db/blob/blob_log_format.cc",
-        "db/blob/blob_log_reader.cc",
+        "db/blob/blob_log_sequential_reader.cc",
         "db/blob/blob_log_writer.cc",
         "db/builder.cc",
         "db/c.cc",
@@ -427,7 +427,7 @@ cpp_library(
         "db/blob/blob_file_meta.cc",
         "db/blob/blob_file_reader.cc",
         "db/blob/blob_log_format.cc",
-        "db/blob/blob_log_reader.cc",
+        "db/blob/blob_log_sequential_reader.cc",
         "db/blob/blob_log_writer.cc",
         "db/builder.cc",
         "db/c.cc",

db/blob/blob_file_builder_test.cc

@@ -14,7 +14,7 @@
 #include "db/blob/blob_file_addition.h"
 #include "db/blob/blob_index.h"
 #include "db/blob/blob_log_format.h"
-#include "db/blob/blob_log_reader.h"
+#include "db/blob/blob_log_sequential_reader.h"
 #include "env/composite_env_wrapper.h"
 #include "env/mock_env.h"
 #include "file/filename.h"
@@ -61,8 +61,8 @@ class BlobFileBuilderTest : public testing::Test {
                                    &mock_env_));
 
     constexpr Statistics* statistics = nullptr;
-    BlobLogReader blob_log_reader(std::move(file_reader), &mock_env_,
-                                  statistics);
+    BlobLogSequentialReader blob_log_reader(std::move(file_reader), &mock_env_,
+                                            statistics);
 
     BlobLogHeader header;
     ASSERT_OK(blob_log_reader.ReadHeader(&header));
@@ -77,7 +77,7 @@ class BlobFileBuilderTest : public testing::Test {
       uint64_t blob_offset = 0;
 
       ASSERT_OK(blob_log_reader.ReadRecord(
-          &record, BlobLogReader::kReadHeaderKeyBlob, &blob_offset));
+          &record, BlobLogSequentialReader::kReadHeaderKeyBlob, &blob_offset));
 
       // Check the contents of the blob file
       const auto& expected_key_value = expected_key_value_pairs[i];

db/blob/blob_log_sequential_reader.cc

@@ -4,7 +4,7 @@
 //  (found in the LICENSE.Apache file in the root directory).
 //
 
-#include "db/blob/blob_log_reader.h"
+#include "db/blob/blob_log_sequential_reader.h"
 
 #include <algorithm>
 
@@ -14,16 +14,19 @@
 
 namespace ROCKSDB_NAMESPACE {
 
-BlobLogReader::BlobLogReader(
+BlobLogSequentialReader::BlobLogSequentialReader(
     std::unique_ptr<RandomAccessFileReader>&& file_reader, Env* env,
     Statistics* statistics)
     : file_(std::move(file_reader)),
       env_(env),
       statistics_(statistics),
-      buffer_(),
       next_byte_(0) {}
 
-Status BlobLogReader::ReadSlice(uint64_t size, Slice* slice, char* buf) {
+BlobLogSequentialReader::~BlobLogSequentialReader() = default;
+
+Status BlobLogSequentialReader::ReadSlice(uint64_t size, Slice* slice,
+                                          char* buf) {
+  assert(slice);
   assert(file_);
 
   StopWatch read_sw(env_, statistics_, BLOB_DB_BLOB_FILE_READ_MICROS);
@@ -40,7 +43,8 @@ Status BlobLogReader::ReadSlice(uint64_t size, Slice* slice, char* buf) {
   return s;
 }
 
-Status BlobLogReader::ReadHeader(BlobLogHeader* header) {
+Status BlobLogSequentialReader::ReadHeader(BlobLogHeader* header) {
+  assert(header);
   assert(next_byte_ == 0);
 
   static_assert(BlobLogHeader::kSize <= sizeof(header_buf_),
@@ -58,8 +62,10 @@ Status BlobLogReader::ReadHeader(BlobLogHeader* header) {
   return header->DecodeFrom(buffer_);
 }
 
-Status BlobLogReader::ReadRecord(BlobLogRecord* record, ReadLevel level,
-                                 uint64_t* blob_offset) {
+Status BlobLogSequentialReader::ReadRecord(BlobLogRecord* record,
+                                           ReadLevel level,
+                                           uint64_t* blob_offset) {
+  assert(record);
   static_assert(BlobLogRecord::kHeaderSize <= sizeof(header_buf_),
                 "Buffer is smaller than BlobLogRecord::kHeaderSize");
 
@@ -108,7 +114,8 @@ Status BlobLogReader::ReadRecord(BlobLogRecord* record, ReadLevel level,
   return s;
 }
 
-Status BlobLogReader::ReadFooter(BlobLogFooter* footer) {
+Status BlobLogSequentialReader::ReadFooter(BlobLogFooter* footer) {
+  assert(footer);
   static_assert(BlobLogFooter::kSize <= sizeof(header_buf_),
                 "Buffer is smaller than BlobLogFooter::kSize");
 

db/blob/blob_log_sequential_reader.h

@@ -6,28 +6,26 @@
 #pragma once
 
 #include <memory>
-#include <string>
 
 #include "db/blob/blob_log_format.h"
-#include "file/random_access_file_reader.h"
-#include "rocksdb/env.h"
 #include "rocksdb/slice.h"
-#include "rocksdb/statistics.h"
-#include "rocksdb/status.h"
 
 namespace ROCKSDB_NAMESPACE {
 
-class SequentialFileReader;
-class Logger;
+class RandomAccessFileReader;
+class Env;
+class Statistics;
+class Status;
 
 /**
- * BlobLogReader is a general purpose log stream reader implementation. The
- * actual job of reading from the device is implemented by the SequentialFile
- * interface.
+ * BlobLogSequentialReader is a general purpose log stream reader
+ * implementation. The actual job of reading from the device is implemented by
+ * the RandomAccessFileReader interface.
  *
- * Please see Writer for details on the file and record layout.
+ * Please see BlobLogWriter for details on the file and record layout.
  */
-class BlobLogReader {
+
+class BlobLogSequentialReader {
  public:
   enum ReadLevel {
     kReadHeader,
@@ -35,23 +33,22 @@ class BlobLogReader {
     kReadHeaderKeyBlob,
   };
 
-  // Create a reader that will return log records from "*file".
-  // "*file" must remain live while this BlobLogReader is in use.
-  BlobLogReader(std::unique_ptr<RandomAccessFileReader>&& file_reader, Env* env,
-                Statistics* statistics);
+  // Create a reader that will return log records from "*file_reader".
+  BlobLogSequentialReader(std::unique_ptr<RandomAccessFileReader>&& file_reader,
+                          Env* env, Statistics* statistics);
+
   // No copying allowed
-  BlobLogReader(const BlobLogReader&) = delete;
-  BlobLogReader& operator=(const BlobLogReader&) = delete;
+  BlobLogSequentialReader(const BlobLogSequentialReader&) = delete;
+  BlobLogSequentialReader& operator=(const BlobLogSequentialReader&) = delete;
 
-  ~BlobLogReader() = default;
+  ~BlobLogSequentialReader();
 
   Status ReadHeader(BlobLogHeader* header);
 
   // Read the next record into *record.  Returns true if read
-  // successfully, false if we hit end of the input.  May use
-  // "*scratch" as temporary storage.  The contents filled in *record
-  // will only be valid until the next mutating operation on this
-  // reader or the next mutation to *scratch.
+  // successfully, false if we hit end of the input. The contents filled in
+  // *record will only be valid until the next mutating operation on this
+  // reader.
   // If blob_offset is non-null, return offset of the blob through it.
   Status ReadRecord(BlobLogRecord* record, ReadLevel level = kReadHeader,
                     uint64_t* blob_offset = nullptr);
@@ -72,7 +69,7 @@ class BlobLogReader {
   Slice buffer_;
   char header_buf_[BlobLogRecord::kHeaderSize];
 
-  // which byte to read next. For asserting proper usage
+  // which byte to read next
   uint64_t next_byte_;
 };
 

src.mk

@@ -11,7 +11,7 @@ LIB_SOURCES =                                                   \
   db/blob/blob_file_meta.cc                                     \
   db/blob/blob_file_reader.cc                                   \
   db/blob/blob_log_format.cc                                    \
-  db/blob/blob_log_reader.cc                                    \
+  db/blob/blob_log_sequential_reader.cc                         \
   db/blob/blob_log_writer.cc                                    \
   db/builder.cc                                                 \
   db/c.cc                                                       \

utilities/blob_db/blob_db_impl.h

@@ -20,7 +20,6 @@
 #include <vector>
 
 #include "db/blob/blob_log_format.h"
-#include "db/blob/blob_log_reader.h"
 #include "db/blob/blob_log_writer.h"
 #include "db/db_iter.h"
 #include "rocksdb/compaction_filter.h"

utilities/blob_db/blob_file.cc

@@ -61,29 +61,6 @@ std::string BlobFile::PathName() const {
   return BlobFileName(path_to_dir_, file_number_);
 }
 
-std::shared_ptr<BlobLogReader> BlobFile::OpenRandomAccessReader(
-    Env* env, const DBOptions& db_options,
-    const EnvOptions& env_options) const {
-  constexpr size_t kReadaheadSize = 2 * 1024 * 1024;
-  std::unique_ptr<RandomAccessFile> sfile;
-  std::string path_name(PathName());
-  Status s = env->NewRandomAccessFile(path_name, &sfile, env_options);
-  if (!s.ok()) {
-    // report something here.
-    return nullptr;
-  }
-  sfile = NewReadaheadRandomAccessFile(std::move(sfile), kReadaheadSize);
-
-  std::unique_ptr<RandomAccessFileReader> sfile_reader;
-  sfile_reader.reset(new RandomAccessFileReader(
-      NewLegacyRandomAccessFileWrapper(sfile), path_name));
-
-  std::shared_ptr<BlobLogReader> log_reader = std::make_shared<BlobLogReader>(
-      std::move(sfile_reader), db_options.env, db_options.statistics.get());
-
-  return log_reader;
-}
-
 std::string BlobFile::DumpState() const {
   char str[1000];
   snprintf(

utilities/blob_db/blob_file.h

@@ -11,7 +11,6 @@
 #include <unordered_set>
 
 #include "db/blob/blob_log_format.h"
-#include "db/blob/blob_log_reader.h"
 #include "db/blob/blob_log_writer.h"
 #include "file/random_access_file_reader.h"
 #include "port/port.h"
@@ -216,10 +215,6 @@ class BlobFile {
                    bool* fresh_open);
 
  private:
-  std::shared_ptr<BlobLogReader> OpenRandomAccessReader(
-      Env* env, const DBOptions& db_options,
-      const EnvOptions& env_options) const;
-
   Status ReadFooter(BlobLogFooter* footer);
 
   Status WriteFooterAndCloseLocked(SequenceNumber sequence);