Support direct IO in RandomAccessFileReader::MultiRead (#6446)

Summary:
By supporting direct IO in RandomAccessFileReader::MultiRead, the benefits of parallel IO (IO uring) and direct IO can be combined.

In direct IO mode, read requests are aligned and merged together before being issued to RandomAccessFile::MultiRead, so blocks in the original requests might share the same underlying buffer, the shared buffers are returned in `aligned_bufs`, which is a new parameter of the `MultiRead` API.

For example, suppose alignment requirement for direct IO is 4KB, one request is (offset: 1KB, len: 1KB), another request is (offset: 3KB, len: 1KB), then since they all belong to page (offset: 0, len: 4KB), `MultiRead` only reads the page with direct IO into a buffer on heap, and returns 2 Slices referencing regions in that same buffer. See `random_access_file_reader_test.cc` for more examples.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6446

Test Plan: Added a new test `random_access_file_reader_test.cc`.

Reviewed By: anand1976

Differential Revision: D20097518

Pulled By: cheng-chang

fbshipit-source-id: ca48a8faf9c3af146465c102ef6b266a363e78d1

CMakeLists.txt

@@ -1022,6 +1022,7 @@ if(WITH_TESTS)
         env/io_posix_test.cc
         env/mock_env_test.cc
         file/delete_scheduler_test.cc
+        file/random_access_file_reader_test.cc
         logging/auto_roll_logger_test.cc
         logging/env_logger_test.cc
         logging/event_logger_test.cc

Makefile

@@ -513,6 +513,7 @@ TESTS = \
 	fault_injection_test \
 	filelock_test \
 	filename_test \
+	random_access_file_reader_test \
 	file_reader_writer_test \
 	block_based_filter_block_test \
 	full_filter_block_test \
@@ -1505,6 +1506,9 @@ delete_scheduler_test: file/delete_scheduler_test.o $(LIBOBJECTS) $(TESTHARNESS)
 filename_test: db/filename_test.o $(LIBOBJECTS) $(TESTHARNESS)
 	$(AM_LINK)
 
+random_access_file_reader_test: file/random_access_file_reader_test.o $(LIBOBJECTS) $(TESTHARNESS) $(TESTUTIL)
+	$(AM_LINK)
+
 file_reader_writer_test: util/file_reader_writer_test.o $(LIBOBJECTS) $(TESTHARNESS)
 	$(AM_LINK)
 

TARGETS

@@ -1300,6 +1300,13 @@ ROCKS_TESTS = [
         [],
         [],
     ],
+    [
+        "random_access_file_reader_test",
+        "file/random_access_file_reader_test.cc",
+        "serial",
+        [],
+        [],
+    ],
     [
         "random_test",
         "util/random_test.cc",

file/random_access_file_reader.cc

@@ -20,11 +20,11 @@
 #include "util/rate_limiter.h"
 
 namespace ROCKSDB_NAMESPACE {
+
 Status RandomAccessFileReader::Read(uint64_t offset, size_t n, Slice* result,
-                                    char* scratch,
+                                    char* scratch, AlignedBuf* aligned_buf,
-                                    std::unique_ptr<const char[]>* internal_buf,
                                     bool for_compaction) const {
-  (void) internal_buf;
+  (void)aligned_buf;
   Status s;
   uint64_t elapsed = 0;
   {
@@ -81,11 +81,11 @@ Status RandomAccessFileReader::Read(uint64_t offset, size_t n, Slice* result,
       size_t res_len = 0;
       if (s.ok() && offset_advance < buf.CurrentSize()) {
         res_len = std::min(buf.CurrentSize() - offset_advance, n);
-        if (internal_buf == nullptr) {
+        if (aligned_buf == nullptr) {
           buf.Read(scratch, offset_advance, res_len);
         } else {
           scratch = buf.BufferStart();
-          internal_buf->reset(buf.Release());
+          aligned_buf->reset(buf.Release());
         }
       }
       *result = Slice(scratch, res_len);
@@ -154,11 +154,44 @@ Status RandomAccessFileReader::Read(uint64_t offset, size_t n, Slice* result,
   return s;
 }
 
+size_t End(const FSReadRequest& r) {
+  return static_cast<size_t>(r.offset) + r.len;
+}
+
+FSReadRequest Align(const FSReadRequest& r, size_t alignment) {
+  FSReadRequest req;
+  req.offset = static_cast<uint64_t>(
+    TruncateToPageBoundary(alignment, static_cast<size_t>(r.offset)));
+  req.len = Roundup(End(r), alignment) - req.offset;
+  return req;
+}
+
+// Try to merge src to dest if they have overlap.
+//
+// Each request represents an inclusive interval [offset, offset + len].
+// If the intervals have overlap, update offset and len to represent the
+// merged interval, and return true.
+// Otherwise, do nothing and return false.
+bool TryMerge(FSReadRequest* dest, const FSReadRequest& src) {
+  size_t dest_offset = static_cast<size_t>(dest->offset);
+  size_t src_offset = static_cast<size_t>(src.offset);
+  size_t dest_end = End(*dest);
+  size_t src_end = End(src);
+  if (std::max(dest_offset, dest_offset) > std::min(dest_end, src_end)) {
+    return false;
+  }
+  dest->offset = static_cast<uint64_t>(std::min(dest_offset, src_offset));
+  dest->len = std::max(dest_end, src_end) - dest->offset;
+  return true;
+}
+
 Status RandomAccessFileReader::MultiRead(FSReadRequest* read_reqs,
-                                         size_t num_reqs) const {
+                                         size_t num_reqs,
+                                         AlignedBuf* aligned_buf) const {
+  (void)aligned_buf;  // suppress warning of unused variable in LITE mode
+  assert(num_reqs > 0);
   Status s;
   uint64_t elapsed = 0;
-  assert(!use_direct_io());
   {
     StopWatch sw(env_, stats_, hist_type_,
                  (stats_ != nullptr) ? &elapsed : nullptr, true /*overwrite*/,
@@ -166,6 +199,44 @@ Status RandomAccessFileReader::MultiRead(FSReadRequest* read_reqs,
     auto prev_perf_level = GetPerfLevel();
     IOSTATS_TIMER_GUARD(read_nanos);
 
+    FSReadRequest* fs_reqs = read_reqs;
+    size_t num_fs_reqs = num_reqs;
+#ifndef ROCKSDB_LITE
+    std::vector<FSReadRequest> aligned_reqs;
+    if (use_direct_io()) {
+      // num_reqs is the max possible size,
+      // this can reduce std::vecector's internal resize operations.
+      aligned_reqs.reserve(num_reqs);
+      // Align and merge the read requests.
+      size_t alignment = file_->GetRequiredBufferAlignment();
+      aligned_reqs.push_back(Align(read_reqs[0], alignment));
+      for (size_t i = 1; i < num_reqs; i++) {
+        const auto& r = Align(read_reqs[i], alignment);
+        if (!TryMerge(&aligned_reqs.back(), r)) {
+          aligned_reqs.push_back(r);
+        }
+      }
+
+      // Allocate aligned buffer and let scratch buffers point to it.
+      size_t total_len = 0;
+      for (const auto& r : aligned_reqs) {
+        total_len += r.len;
+      }
+      AlignedBuffer buf;
+      buf.Alignment(alignment);
+      buf.AllocateNewBuffer(total_len);
+      char* scratch = buf.BufferStart();
+      for (auto& r : aligned_reqs) {
+        r.scratch = scratch;
+        scratch += r.len;
+      }
+
+      aligned_buf->reset(buf.Release());
+      fs_reqs = aligned_reqs.data();
+      num_fs_reqs = aligned_reqs.size();
+    }
+#endif  // ROCKSDB_LITE
+
 #ifndef ROCKSDB_LITE
     FileOperationInfo::TimePoint start_ts;
     if (ShouldNotifyListeners()) {
@@ -174,8 +245,31 @@ Status RandomAccessFileReader::MultiRead(FSReadRequest* read_reqs,
 #endif  // ROCKSDB_LITE
     {
       IOSTATS_CPU_TIMER_GUARD(cpu_read_nanos, env_);
-      s = file_->MultiRead(read_reqs, num_reqs, IOOptions(), nullptr);
+      s = file_->MultiRead(fs_reqs, num_fs_reqs, IOOptions(), nullptr);
     }
+
+#ifndef ROCKSDB_LITE
+    if (use_direct_io()) {
+      // Populate results in the unaligned read requests.
+      size_t aligned_i = 0;
+      for (size_t i = 0; i < num_reqs; i++) {
+        auto& r = read_reqs[i];
+        if (static_cast<size_t>(r.offset) > End(aligned_reqs[aligned_i])) {
+          aligned_i++;
+        }
+        const auto& fs_r = fs_reqs[aligned_i];
+        r.status = fs_r.status;
+        if (r.status.ok()) {
+          uint64_t offset = r.offset - fs_r.offset;
+          size_t len = std::min(r.len, static_cast<size_t>(fs_r.len - offset));
+          r.result = Slice(fs_r.scratch + offset, len);
+        } else {
+          r.result = Slice();
+        }
+      }
+    }
+#endif  // ROCKSDB_LITE
+
     for (size_t i = 0; i < num_reqs; ++i) {
 #ifndef ROCKSDB_LITE
       if (ShouldNotifyListeners()) {
@@ -194,4 +288,5 @@ Status RandomAccessFileReader::MultiRead(FSReadRequest* read_reqs,
 
   return s;
 }
+
 }  // namespace ROCKSDB_NAMESPACE

file/random_access_file_reader.h

@@ -22,6 +22,8 @@ namespace ROCKSDB_NAMESPACE {
 class Statistics;
 class HistogramImpl;
 
+using AlignedBuf = std::unique_ptr<const char[]>;
+
 // RandomAccessFileReader is a wrapper on top of Env::RnadomAccessFile. It is
 // responsible for:
 // - Handling Buffered and Direct reads appropriately.
@@ -59,7 +61,7 @@ class RandomAccessFileReader {
 
  public:
   explicit RandomAccessFileReader(
-      std::unique_ptr<FSRandomAccessFile>&& raf, std::string _file_name,
+      std::unique_ptr<FSRandomAccessFile>&& raf, const std::string& _file_name,
       Env* env = nullptr, Statistics* stats = nullptr, uint32_t hist_type = 0,
       HistogramImpl* file_read_hist = nullptr,
       RateLimiter* rate_limiter = nullptr,
@@ -106,17 +108,22 @@ class RandomAccessFileReader {
   // 1. if using mmap, result is stored in a buffer other than scratch;
   // 2. if not using mmap, result is stored in the buffer starting from scratch.
   //
-  // In direct IO mode, an internal aligned buffer is allocated.
+  // In direct IO mode, an aligned buffer is allocated internally.
-  // 1. If internal_buf is null, then results are copied to the buffer
+  // 1. If aligned_buf is null, then results are copied to the buffer
   // starting from scratch;
-  // 2. Otherwise, scratch is not used and can be null, the internal_buf owns
+  // 2. Otherwise, scratch is not used and can be null, the aligned_buf owns
   // the internally allocated buffer on return, and the result refers to a
-  // region in internal_buf.
+  // region in aligned_buf.
   Status Read(uint64_t offset, size_t n, Slice* result, char* scratch,
-              std::unique_ptr<const char[]>* internal_buf,
+              AlignedBuf* aligned_buf, bool for_compaction = false) const;
-              bool for_compaction = false) const;
 
-  Status MultiRead(FSReadRequest* reqs, size_t num_reqs) const;
+  // REQUIRES:
+  // num_reqs > 0, reqs do not overlap, and offsets in reqs are increasing.
+  // In non-direct IO mode, aligned_buf should be null;
+  // In direct IO mode, aligned_buf stores the aligned buffer allocated inside
+  // MultiRead, the result Slices in reqs refer to aligned_buf.
+  Status MultiRead(FSReadRequest* reqs, size_t num_reqs,
+                   AlignedBuf* aligned_buf) const;
 
   Status Prefetch(uint64_t offset, size_t n) const {
     return file_->Prefetch(offset, n, IOOptions(), nullptr);

file/random_access_file_reader_test.cc

@@ -0,0 +1,255 @@
+//  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 "port/port.h"
+#include "port/stack_trace.h"
+#include "rocksdb/file_system.h"
+#include "file/random_access_file_reader.h"
+#include "test_util/testharness.h"
+#include "test_util/testutil.h"
+
+namespace ROCKSDB_NAMESPACE {
+
+class RandomAccessFileReaderTest : public testing::Test {
+ public:
+  void SetUp() override {
+#ifdef OS_LINUX
+    // TEST_TMPDIR may be set to /dev/shm in Makefile,
+    // but /dev/shm does not support direct IO.
+    // The default TEST_TMPDIR is under /tmp, but /tmp might also be a tmpfs
+    // which does not support direct IO neither.
+    unsetenv("TEST_TMPDIR");
+    char* tmpdir = getenv("DISK_TEMP_DIR");
+    if (tmpdir == nullptr) {
+      tmpdir = getenv("HOME");
+    }
+    if (tmpdir != nullptr) {
+      setenv("TEST_TMPDIR", tmpdir, 1);
+    }
+#endif
+    env_ = Env::Default();
+    fs_ = FileSystem::Default();
+    test_dir_ = test::PerThreadDBPath("random_access_file_reader_test");
+    ASSERT_OK(fs_->CreateDir(test_dir_, IOOptions(), nullptr));
+    alignment_ = GetAlignment();
+  }
+
+  void TearDown() override {
+    EXPECT_OK(test::DestroyDir(env_, test_dir_));
+  }
+
+  bool IsDirectIOSupported() {
+    Write(".direct", "");
+    FileOptions opt;
+    opt.use_direct_reads = true;
+    std::unique_ptr<FSRandomAccessFile> f;
+    auto s = fs_->NewRandomAccessFile(Path(".direct"), opt, &f, nullptr);
+    return s.ok();
+  }
+
+  void Write(const std::string& fname, const std::string& content) {
+    std::unique_ptr<FSWritableFile> f;
+    ASSERT_OK(fs_->NewWritableFile(Path(fname), FileOptions(), &f, nullptr));
+    ASSERT_OK(f->Append(content, IOOptions(), nullptr));
+    ASSERT_OK(f->Close(IOOptions(), nullptr));
+  }
+
+  void Read(const std::string& fname, const FileOptions& opts,
+                std::unique_ptr<RandomAccessFileReader>* reader) {
+    std::string fpath = Path(fname);
+    std::unique_ptr<FSRandomAccessFile> f;
+    ASSERT_OK(fs_->NewRandomAccessFile(fpath, opts, &f, nullptr));
+    (*reader).reset(new RandomAccessFileReader(std::move(f), fpath, env_));
+  }
+
+  void AssertResult(const std::string& content,
+                    const std::vector<FSReadRequest>& reqs) {
+    for (const auto& r : reqs) {
+      ASSERT_OK(r.status);
+      ASSERT_EQ(r.len, r.result.size());
+      ASSERT_EQ(content.substr(r.offset, r.len), r.result.ToString());
+    }
+  }
+
+  size_t alignment() const { return alignment_; }
+
+ private:
+  Env* env_;
+  std::shared_ptr<FileSystem> fs_;
+  std::string test_dir_;
+  size_t alignment_;
+
+  std::string Path(const std::string& fname) {
+    return test_dir_ + "/" + fname;
+  }
+
+  size_t GetAlignment() {
+    std::string f = "get_alignment";
+    Write(f, "");
+    std::unique_ptr<RandomAccessFileReader> r;
+    Read(f, FileOptions(), &r);
+    size_t alignment = r->file()->GetRequiredBufferAlignment();
+    EXPECT_OK(fs_->DeleteFile(Path(f), IOOptions(), nullptr));
+    return alignment;
+  }
+};
+
+TEST_F(RandomAccessFileReaderTest, MultiReadDirectIO) {
+  if (!IsDirectIOSupported()) {
+    printf("Direct IO is not supported, skip this test\n");
+    return;
+  }
+
+  // Creates a file with 3 pages.
+  std::string fname = "multi-read-direct-io";
+  Random rand(0);
+  std::string content;
+  test::RandomString(&rand, 3 * static_cast<int>(alignment()), &content);
+  Write(fname, content);
+
+  FileOptions opts;
+  opts.use_direct_reads = true;
+  std::unique_ptr<RandomAccessFileReader> r;
+  Read(fname, opts, &r);
+  ASSERT_TRUE(r->use_direct_io());
+
+  {
+    // Reads 2 blocks in the 1st page.
+    // The results should be SharedSlices of the same underlying buffer.
+    //
+    // Illustration (each x is a 1/4 page)
+    // First page: xxxx
+    // 1st block:  x
+    // 2nd block:    xx
+    FSReadRequest r0;
+    r0.offset = 0;
+    r0.len = alignment() / 4;
+    r0.scratch = nullptr;
+
+    FSReadRequest r1;
+    r1.offset = alignment() / 2;
+    r1.len = alignment() / 2;
+    r1.scratch = nullptr;
+
+    std::vector<FSReadRequest> reqs;
+    reqs.push_back(std::move(r0));
+    reqs.push_back(std::move(r1));
+    AlignedBuf aligned_buf;
+    ASSERT_OK(r->MultiRead(reqs.data(), reqs.size(), &aligned_buf));
+
+    AssertResult(content, reqs);
+  }
+
+  {
+    // Reads 3 blocks:
+    // 1st block in the 1st page;
+    // 2nd block from the middle of the 1st page to the middle of the 2nd page;
+    // 3rd block in the 2nd page.
+    // The results should be SharedSlices of the same underlying buffer.
+    //
+    // Illustration (each x is a 1/4 page)
+    // 2 pages:   xxxxxxxx
+    // 1st block: x
+    // 2nd block:   xxxx
+    // 3rd block:        x
+    FSReadRequest r0;
+    r0.offset = 0;
+    r0.len = alignment() / 4;
+    r0.scratch = nullptr;
+
+    FSReadRequest r1;
+    r1.offset = alignment() / 2;
+    r1.len = alignment();
+    r1.scratch = nullptr;
+
+    FSReadRequest r2;
+    r2.offset = 2 * alignment() - alignment() / 4;
+    r2.len = alignment() / 4;
+    r2.scratch = nullptr;
+
+    std::vector<FSReadRequest> reqs;
+    reqs.push_back(std::move(r0));
+    reqs.push_back(std::move(r1));
+    reqs.push_back(std::move(r2));
+    AlignedBuf aligned_buf;
+    ASSERT_OK(r->MultiRead(reqs.data(), reqs.size(), &aligned_buf));
+
+    AssertResult(content, reqs);
+  }
+
+  {
+    // Reads 3 blocks:
+    // 1st block in the middle of the 1st page;
+    // 2nd block in the middle of the 2nd page;
+    // 3rd block in the middle of the 3rd page.
+    // The results should be SharedSlices of the same underlying buffer.
+    //
+    // Illustration (each x is a 1/4 page)
+    // 3 pages:   xxxxxxxxxxxx
+    // 1st block:  xx
+    // 2nd block:      xx
+    // 3rd block:          xx
+    FSReadRequest r0;
+    r0.offset = alignment() / 4;
+    r0.len = alignment() / 2;
+    r0.scratch = nullptr;
+
+    FSReadRequest r1;
+    r1.offset = alignment() + alignment() / 4;
+    r1.len = alignment() / 2;
+    r1.scratch = nullptr;
+
+    FSReadRequest r2;
+    r2.offset = 2 * alignment() + alignment() / 4;
+    r2.len = alignment() / 2;
+    r2.scratch = nullptr;
+
+    std::vector<FSReadRequest> reqs;
+    reqs.push_back(std::move(r0));
+    reqs.push_back(std::move(r1));
+    reqs.push_back(std::move(r2));
+    AlignedBuf aligned_buf;
+    ASSERT_OK(r->MultiRead(reqs.data(), reqs.size(), &aligned_buf));
+
+    AssertResult(content, reqs);
+  }
+
+  {
+    // Reads 2 blocks:
+    // 1st block in the middle of the 1st page;
+    // 2nd block in the middle of the 3rd page.
+    // The results are two different buffers.
+    //
+    // Illustration (each x is a 1/4 page)
+    // 3 pages:   xxxxxxxxxxxx
+    // 1st block:  xx
+    // 2nd block:          xx
+    FSReadRequest r0;
+    r0.offset = alignment() / 4;
+    r0.len = alignment() / 2;
+    r0.scratch = nullptr;
+
+    FSReadRequest r1;
+    r1.offset = 2 * alignment() + alignment() / 4;
+    r1.len = alignment() / 2;
+    r1.scratch = nullptr;
+
+    std::vector<FSReadRequest> reqs;
+    reqs.push_back(std::move(r0));
+    reqs.push_back(std::move(r1));
+    AlignedBuf aligned_buf;
+    ASSERT_OK(r->MultiRead(reqs.data(), reqs.size(), &aligned_buf));
+
+    AssertResult(content, reqs);
+  }
+}
+
+}  // namespace ROCKSDB_NAMESPACE
+
+int main(int argc, char** argv) {
+  ROCKSDB_NAMESPACE::port::InstallStackTraceHandler();
+  ::testing::InitGoogleTest(&argc, argv);
+  return RUN_ALL_TESTS();
+}

port/win/env_win.cc

@@ -1424,7 +1424,7 @@ Status WinEnv::UnlockFile(FileLock* lock) {
   return winenv_io_.UnlockFile(lock);
 }
 
-Status  WinEnv::GetTestDirectory(std::string* result) {
+Status WinEnv::GetTestDirectory(std::string* result) {
   return winenv_io_.GetTestDirectory(result);
 }
 

src.mk

@@ -395,6 +395,7 @@ MAIN_SOURCES =                                                          \
   env/env_test.cc                                                       \
   env/io_posix_test.cc                                                  \
   env/mock_env_test.cc                                                  \
+  file/random_access_file_reader_test.cc                                \
   logging/auto_roll_logger_test.cc                                      \
   logging/env_logger_test.cc                                            \
   logging/event_logger_test.cc                                          \

table/block_based/block_based_table_reader.cc

@@ -1607,7 +1607,6 @@ void BlockBasedTable::RetrieveMultipleBlocks(
           req.scratch = scratch + buf_offset;
           buf_offset += req.len;
         }
-        req.status = IOStatus::OK();
         read_reqs.emplace_back(req);
       }
 
@@ -1628,11 +1627,10 @@ void BlockBasedTable::RetrieveMultipleBlocks(
     } else {
       req.scratch = scratch + buf_offset;
     }
-    req.status = IOStatus::OK();
     read_reqs.emplace_back(req);
   }
 
-  file->MultiRead(&read_reqs[0], read_reqs.size());
+  file->MultiRead(&read_reqs[0], read_reqs.size(), nullptr);
 
   idx_in_batch = 0;
   size_t valid_batch_idx = 0;
@@ -1699,7 +1697,7 @@ void BlockBasedTable::RetrieveMultipleBlocks(
         // in each read request. Checksum is stored in the block trailer,
         // which is handle.size() + 1.
         s = ROCKSDB_NAMESPACE::VerifyChecksum(footer.checksum(),
-                                              req.result.data() + req_offset,
+                                              data + req_offset,
                                               handle.size() + 1, expected);
         TEST_SYNC_POINT_CALLBACK("RetrieveMultipleBlocks:VerifyChecksum", &s);
       }

utilities/blob_db/blob_db_impl.cc

@@ -1483,7 +1483,7 @@ Status BlobDBImpl::GetRawBlobFromFile(const Slice& key, uint64_t file_number,
 
   // Allocate the buffer. This is safe in C++11
   std::string buf;
-  std::unique_ptr<const char[]> internal_buf;
+  AlignedBuf aligned_buf;
 
   // A partial blob record contain checksum, key and value.
   Slice blob_record;
@@ -1492,11 +1492,11 @@ Status BlobDBImpl::GetRawBlobFromFile(const Slice& key, uint64_t file_number,
     StopWatch read_sw(env_, statistics_, BLOB_DB_BLOB_FILE_READ_MICROS);
     if (reader->use_direct_io()) {
       s = reader->Read(record_offset, static_cast<size_t>(record_size),
-                      &blob_record, nullptr, &internal_buf);
+                       &blob_record, nullptr, &aligned_buf);
     } else {
       buf.reserve(static_cast<size_t>(record_size));
       s = reader->Read(record_offset, static_cast<size_t>(record_size),
-                      &blob_record, &buf[0], nullptr);
+                       &blob_record, &buf[0], nullptr);
     }
     RecordTick(statistics_, BLOB_DB_BLOB_FILE_BYTES_READ, blob_record.size());
   }

utilities/blob_db/blob_file.cc

@@ -139,11 +139,11 @@ Status BlobFile::ReadFooter(BlobLogFooter* bf) {
 
   Slice result;
   std::string buf;
-  std::unique_ptr<const char[]> internal_buf;
+  AlignedBuf aligned_buf;
   Status s;
   if (ra_file_reader_->use_direct_io()) {
     s = ra_file_reader_->Read(footer_offset, BlobLogFooter::kSize, &result,
-                              nullptr, &internal_buf);
+                              nullptr, &aligned_buf);
   } else {
     buf.reserve(BlobLogFooter::kSize + 10);
     s = ra_file_reader_->Read(footer_offset, BlobLogFooter::kSize, &result,
@@ -263,11 +263,11 @@ Status BlobFile::ReadMetadata(Env* env, const EnvOptions& env_options) {
 
   // Read file header.
   std::string header_buf;
-  std::unique_ptr<const char[]> internal_buf;
+  AlignedBuf aligned_buf;
   Slice header_slice;
   if (file_reader->use_direct_io()) {
     s = file_reader->Read(0, BlobLogHeader::kSize, &header_slice, nullptr,
-                          &internal_buf);
+                          &aligned_buf);
   } else {
     header_buf.reserve(BlobLogHeader::kSize);
     s = file_reader->Read(0, BlobLogHeader::kSize, &header_slice,
@@ -306,12 +306,14 @@ Status BlobFile::ReadMetadata(Env* env, const EnvOptions& env_options) {
   std::string footer_buf;
   Slice footer_slice;
   if (file_reader->use_direct_io()) {
-    s = file_reader->Read(file_size - BlobLogFooter::kSize, BlobLogFooter::kSize,
+    s = file_reader->Read(file_size - BlobLogFooter::kSize,
-                          &footer_slice, nullptr, &internal_buf);
+                          BlobLogFooter::kSize, &footer_slice, nullptr,
+                          &aligned_buf);
   } else {
     footer_buf.reserve(BlobLogFooter::kSize);
-    s = file_reader->Read(file_size - BlobLogFooter::kSize, BlobLogFooter::kSize,
+    s = file_reader->Read(file_size - BlobLogFooter::kSize,
-                          &footer_slice, &footer_buf[0], nullptr);
+                          BlobLogFooter::kSize, &footer_slice, &footer_buf[0],
+                          nullptr);
   }
   if (!s.ok()) {
     ROCKS_LOG_ERROR(info_log_,