Merge pull request #798 from yuslepukhin/readahead_buffermanagement

Implement smart buffer management in Windows Env.

db/db_bench.cc

@@ -373,6 +373,9 @@ DEFINE_int32(new_table_reader_for_compaction_inputs, true,
 
 DEFINE_int32(compaction_readahead_size, 0, "Compaction readahead size");
 
+DEFINE_int32(random_access_max_buffer_size, 1024 * 1024,
+             "Maximum windows randomaccess buffer size");
+
 DEFINE_int32(bloom_bits, -1, "Bloom filter bits per key. Negative means"
              " use default settings.");
 DEFINE_int32(memtable_bloom_bits, 0, "Bloom filter bits per key for memtable. "
@@ -2295,6 +2298,7 @@ class Benchmark {
     options.new_table_reader_for_compaction_inputs =
         FLAGS_new_table_reader_for_compaction_inputs;
     options.compaction_readahead_size = FLAGS_compaction_readahead_size;
+    options.random_access_max_buffer_size = FLAGS_random_access_max_buffer_size;
     options.statistics = dbstats;
     if (FLAGS_enable_io_prio) {
       FLAGS_env->LowerThreadPoolIOPriority(Env::LOW);

include/rocksdb/env.h

@@ -88,6 +88,12 @@ struct EnvOptions {
   // WAL writes
   bool fallocate_with_keep_size = true;
 
+  // See DBOPtions doc
+  size_t compaction_readahead_size;
+
+  // See DBOPtions doc
+  size_t random_access_max_buffer_size;
+
   // If not nullptr, write rate limiting is enabled for flush and compaction
   RateLimiter* rate_limiter = nullptr;
 };
@@ -408,6 +414,11 @@ class RandomAccessFile {
     return false;
   }
 
+  // For cases when read-ahead is implemented in the platform dependent
+  // layer
+  virtual void EnableReadAhead() {
+  }
+
   // Tries to get an unique ID for this file that will be the same each time
   // the file is opened (and will stay the same while the file is open).
   // Furthermore, it tries to make this ID at most "max_size" bytes. If such an

include/rocksdb/options.h

@@ -1075,6 +1075,20 @@ struct DBOptions {
   // Default: 0
   size_t compaction_readahead_size;
 
+  // This is a maximum buffer size that is used by WinMmapReadableFile in
+  // unbuffered disk I/O mode. We need to maintain an aligned buffer for
+  // reads. We allow the buffer to grow until the specified value and then
+  // for bigger requests allocate one shot buffers. In unbuffered mode we
+  // always bypass read-ahead buffer at ReadaheadRandomAccessFile
+  // When read-ahead is required we then make use of compaction_readahead_size
+  // value and always try to read ahead. With read-ahead we always
+  // pre-allocate buffer to the size instead of growing it up to a limit.
+  //
+  // This option is currently honored only on Windows
+  //
+  // Default: 1 Mb
+  size_t random_access_max_buffer_size;
+
   // Use adaptive mutex, which spins in the user space before resorting
   // to kernel. This could reduce context switch when the mutex is not
   // heavily contended. However, if the mutex is hot, we could end up

port/win/env_win.cc

@@ -688,28 +688,98 @@ class WinRandomAccessFile : public RandomAccessFile {
   const std::string filename_;
   HANDLE hFile_;
   const bool use_os_buffer_;
+  bool    read_ahead_;
+  const size_t  compaction_readahead_size_;
+  const size_t  random_access_max_buffer_size_;
   mutable std::mutex buffer_mut_;
   mutable AlignedBuffer buffer_;
   mutable uint64_t
       buffered_start_;  // file offset set that is currently buffered
 
+  /*
+   * The function reads a requested amount of bytes into the specified aligned buffer
+   * Upon success the function sets the length of the buffer to the amount of bytes actually
+   * read even though it might be less than actually requested.
+   * It then copies the amount of bytes requested by the user (left) to the user supplied
+   * buffer (dest) and reduces left by the amount of bytes copied to the user buffer
+   *
+   * @user_offset [in] - offset on disk where the read was requested by the user
+   * @first_page_start [in] - actual page aligned disk offset that we want to read from
+   * @bytes_to_read [in] - total amount of bytes that will be read from disk which is generally
+   *                     greater or equal to the amount that the user has requested due to the
+   *                     either alignment requirements or read_ahead in effect.
+   * @left [in/out] total amount of bytes that needs to be copied to the user buffer. It is reduced
+   *                by the amount of bytes that actually copied
+   * @buffer - buffer to use
+   * @dest - user supplied buffer
+  */
+  SSIZE_T ReadIntoBuffer(uint64_t user_offset, uint64_t first_page_start,
+    size_t bytes_to_read, size_t& left, AlignedBuffer& buffer, char* dest) const {
+
+    assert(buffer.CurrentSize() == 0);
+    assert(buffer.Capacity() >= bytes_to_read);
+
+    SSIZE_T read = pread(hFile_, buffer.Destination(), bytes_to_read,
+      first_page_start);
+
+    if (read > 0) {
+      buffer.Size(read);
+
+      // Let's figure out how much we read from the users standpoint
+      if ((first_page_start + buffer.CurrentSize()) > user_offset) {
+        assert(first_page_start <= user_offset);
+        size_t buffer_offset = user_offset - first_page_start;
+        read = buffer.Read(dest, buffer_offset, left);
+      } else {
+        read = 0;
+      }
+      left -= read;
+    }
+    return read;
+  }
+
+  SSIZE_T ReadIntoOneShotBuffer(uint64_t user_offset, uint64_t first_page_start,
+    size_t bytes_to_read, size_t& left, char* dest) const {
+
+    AlignedBuffer bigBuffer;
+    bigBuffer.Alignment(buffer_.Alignment());
+    bigBuffer.AllocateNewBuffer(bytes_to_read);
+
+    return ReadIntoBuffer(user_offset, first_page_start, bytes_to_read, left,
+      bigBuffer, dest);
+  }
+
+  SSIZE_T ReadIntoInstanceBuffer(uint64_t user_offset, uint64_t first_page_start,
+    size_t bytes_to_read, size_t& left, char* dest) const {
+
+    SSIZE_T read = ReadIntoBuffer(user_offset, first_page_start, bytes_to_read,
+      left, buffer_, dest);
+
+    if (read > 0) {
+      buffered_start_ = first_page_start;
+    }
+
+    return read;
+  }
+
  public:
   WinRandomAccessFile(const std::string& fname, HANDLE hFile, size_t alignment,
                       const EnvOptions& options)
       : filename_(fname),
         hFile_(hFile),
         use_os_buffer_(options.use_os_buffer),
+        read_ahead_(false),
+        compaction_readahead_size_(options.compaction_readahead_size),
+        random_access_max_buffer_size_(options.random_access_max_buffer_size),
         buffer_(),
         buffered_start_(0) {
     assert(!options.use_mmap_reads);
 
     // Unbuffered access, use internal buffer for reads
     if (!use_os_buffer_) {
+      // Do not allocate the buffer either until the first request or
+      // until there is a call to allocate a read-ahead buffer
       buffer_.Alignment(alignment);
-      // Random read, no need in a big buffer
-      // We read things in database blocks which are likely to be similar to
-      // the alignment we use.
-      buffer_.AllocateNewBuffer(alignment * 2);
     }
   }
 
@@ -719,6 +789,10 @@ class WinRandomAccessFile : public RandomAccessFile {
     }
   }
 
+  virtual void EnableReadAhead() override {
+    this->Hint(SEQUENTIAL);
+  }
+
   virtual Status Read(uint64_t offset, size_t n, Slice* result,
                       char* scratch) const override {
     Status s;
@@ -730,7 +804,7 @@ class WinRandomAccessFile : public RandomAccessFile {
     // - use our own aligned buffer
     // - always read at the offset of that is a multiple of alignment
     if (!use_os_buffer_) {
-      std::lock_guard<std::mutex> lg(buffer_mut_);
+      std::unique_lock<std::mutex> lock(buffer_mut_);
 
       // Let's see if at least some of the requested data is already
       // in the buffer
@@ -749,40 +823,40 @@ class WinRandomAccessFile : public RandomAccessFile {
       if (left > 0) {
         // Figure out the start/end offset for reading and amount to read
         const size_t alignment = buffer_.Alignment();
-        const size_t start_page_start =
+        const size_t first_page_start =
           TruncateToPageBoundary(alignment, offset);
-        const size_t end_page_start =
-            TruncateToPageBoundary(alignment, offset + left - 1);
-        const size_t actual_bytes_toread =
-            (end_page_start - start_page_start) + alignment;
 
-        if (buffer_.Capacity() < actual_bytes_toread) {
-          buffer_.AllocateNewBuffer(actual_bytes_toread);
-        } else {
-          buffer_.Clear();
+        size_t bytes_requested = left;
+        if (read_ahead_ && bytes_requested < compaction_readahead_size_) {
+          bytes_requested = compaction_readahead_size_;
         }
 
-        SSIZE_T read = 0;
-        read = pread(hFile_, buffer_.Destination(), actual_bytes_toread,
-                      start_page_start);
-
-        if (read > 0) {
-          buffer_.Size(read);
-          buffered_start_ = start_page_start;
+        const size_t last_page_start =
+          TruncateToPageBoundary(alignment, offset + bytes_requested - 1);
+        const size_t actual_bytes_toread =
+          (last_page_start - first_page_start) + alignment;
 
-          // Let's figure out how much we read from the users standpoint
-          if ((buffered_start_ + uint64_t(read)) > offset) {
-            size_t buffer_offset = offset - buffered_start_;
-            r = buffer_.Read(dest, buffer_offset, left);
+        if (buffer_.Capacity() < actual_bytes_toread) {
+          // If we are in read-ahead mode or the requested size
+          // exceeds max buffer size then use one-shot
+          // big buffer otherwise reallocate main buffer
+          if (read_ahead_ ||
+            (actual_bytes_toread > random_access_max_buffer_size_)) {
+            // Unlock the mutex since we are not using instance buffer
+            lock.unlock();
+            r = ReadIntoOneShotBuffer(offset, first_page_start,
+              actual_bytes_toread, left, dest);
           } else {
-            r = 0;
+            buffer_.AllocateNewBuffer(actual_bytes_toread);
+            r = ReadIntoInstanceBuffer(offset, first_page_start,
+              actual_bytes_toread, left, dest);
           }
-          left -= r;
         } else {
-          r = read;
+          buffer_.Clear();
+          r = ReadIntoInstanceBuffer(offset, first_page_start,
+            actual_bytes_toread, left, dest);
         }
       }
-
     } else {
       r = pread(hFile_, scratch, left, offset);
       if (r > 0) {
@@ -802,7 +876,23 @@ class WinRandomAccessFile : public RandomAccessFile {
     return true;
   }
 
-  virtual void Hint(AccessPattern pattern) override {}
+  virtual void Hint(AccessPattern pattern) override {
+
+    if (pattern == SEQUENTIAL &&
+        !use_os_buffer_ &&
+        compaction_readahead_size_ > 0) {
+      std::lock_guard<std::mutex> lg(buffer_mut_);
+      if (!read_ahead_) {
+        read_ahead_ = true;
+        // This would allocate read-ahead size + 2 alignments
+        // - one for memory alignment which added implicitly by AlignedBuffer
+        // - We add one more alignment because we will read one alignment more
+        // from disk
+        buffer_.AllocateNewBuffer(compaction_readahead_size_ + buffer_.Alignment());
+      }
+    }
+  }
+
 
   virtual Status InvalidateCache(size_t offset, size_t length) override {
     return Status::OK();

util/env.cc

@@ -292,6 +292,8 @@ void AssignEnvOptions(EnvOptions* env_options, const DBOptions& options) {
   env_options->use_mmap_writes = options.allow_mmap_writes;
   env_options->set_fd_cloexec = options.is_fd_close_on_exec;
   env_options->bytes_per_sync = options.bytes_per_sync;
+  env_options->compaction_readahead_size = options.compaction_readahead_size;
+  env_options->random_access_max_buffer_size = options.random_access_max_buffer_size;
   env_options->rate_limiter = options.rate_limiter.get();
   env_options->allow_fallocate = options.allow_fallocate;
 }

util/file_reader_writer.cc

@@ -386,9 +386,15 @@ class ReadaheadRandomAccessFile : public RandomAccessFile {
      : file_(std::move(file)),
        readahead_size_(readahead_size),
        forward_calls_(file_->ShouldForwardRawRequest()),
-       buffer_(new char[readahead_size_]),
+       buffer_(),
        buffer_offset_(0),
-       buffer_len_(0) {}
+       buffer_len_(0) {
+     if (!forward_calls_) {
+       buffer_.reset(new char[readahead_size_]);
+     } else if (readahead_size_ > 0) {
+       file_->EnableReadAhead();
+     }
+   }
 
  ReadaheadRandomAccessFile(const ReadaheadRandomAccessFile&) = delete;
 

util/options.cc

@@ -250,6 +250,7 @@ DBOptions::DBOptions()
       access_hint_on_compaction_start(NORMAL),
       new_table_reader_for_compaction_inputs(false),
       compaction_readahead_size(0),
+      random_access_max_buffer_size(1024 * 1024),
       use_adaptive_mutex(false),
       bytes_per_sync(0),
       wal_bytes_per_sync(0),
@@ -310,6 +311,7 @@ DBOptions::DBOptions(const Options& options)
       new_table_reader_for_compaction_inputs(
           options.new_table_reader_for_compaction_inputs),
       compaction_readahead_size(options.compaction_readahead_size),
+      random_access_max_buffer_size(options.random_access_max_buffer_size),
       use_adaptive_mutex(options.use_adaptive_mutex),
       bytes_per_sync(options.bytes_per_sync),
       wal_bytes_per_sync(options.wal_bytes_per_sync),
@@ -403,6 +405,10 @@ void DBOptions::Dump(Logger* log) const {
          "               Options.compaction_readahead_size: %" ROCKSDB_PRIszt
          "d",
          compaction_readahead_size);
+    Header(log,
+        "               Options.random_access_max_buffer_size: %" ROCKSDB_PRIszt
+        "d",
+        random_access_max_buffer_size);
     Header(log, "                      Options.use_adaptive_mutex: %d",
         use_adaptive_mutex);
     Header(log, "                            Options.rate_limiter: %p",

util/options_helper.h

@@ -180,6 +180,9 @@ static std::unordered_map<std::string, OptionTypeInfo> db_options_type_info = {
     {"compaction_readahead_size",
      {offsetof(struct DBOptions, compaction_readahead_size), OptionType::kSizeT,
       OptionVerificationType::kNormal}},
+    {"random_access_max_buffer_size",
+     { offsetof(struct DBOptions, random_access_max_buffer_size), OptionType::kSizeT,
+      OptionVerificationType::kNormal}},
     {"use_adaptive_mutex",
      {offsetof(struct DBOptions, use_adaptive_mutex), OptionType::kBoolean,
       OptionVerificationType::kNormal}},

util/options_test.cc

@@ -339,6 +339,7 @@ TEST_F(OptionsTest, GetOptionsFromMapTest) {
       {"use_adaptive_mutex", "false"},
       {"new_table_reader_for_compaction_inputs", "true"},
       {"compaction_readahead_size", "100"},
+      {"random_access_max_buffer_size", "3145728" },
       {"bytes_per_sync", "47"},
       {"wal_bytes_per_sync", "48"},
   };
@@ -449,6 +450,7 @@ TEST_F(OptionsTest, GetOptionsFromMapTest) {
   ASSERT_EQ(new_db_opt.use_adaptive_mutex, false);
   ASSERT_EQ(new_db_opt.new_table_reader_for_compaction_inputs, true);
   ASSERT_EQ(new_db_opt.compaction_readahead_size, 100);
+  ASSERT_EQ(new_db_opt.random_access_max_buffer_size, 3145728);
   ASSERT_EQ(new_db_opt.bytes_per_sync, static_cast<uint64_t>(47));
   ASSERT_EQ(new_db_opt.wal_bytes_per_sync, static_cast<uint64_t>(48));
 }