1 files changed, 72 insertions, 0 deletions
diff --git a/src/rocksdb/table/block_based/block_prefetcher.h b/src/rocksdb/table/block_based/block_prefetcher.h
new file mode 100644
index 000000000..518868a30
--- /dev/null
+++ b/src/rocksdb/table/block_based/block_prefetcher.h
@@ -0,0 +1,72 @@
+//  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).
+//
+// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file. See the AUTHORS file for names of contributors.
+#pragma once
+#include "table/block_based/block_based_table_reader.h"
+
+namespace ROCKSDB_NAMESPACE {
+class BlockPrefetcher {
+ public:
+  explicit BlockPrefetcher(size_t compaction_readahead_size,
+                           size_t initial_auto_readahead_size)
+      : compaction_readahead_size_(compaction_readahead_size),
+        readahead_size_(initial_auto_readahead_size),
+        initial_auto_readahead_size_(initial_auto_readahead_size) {}
+
+  void PrefetchIfNeeded(const BlockBasedTable::Rep* rep,
+                        const BlockHandle& handle, size_t readahead_size,
+                        bool is_for_compaction,
+                        const bool no_sequential_checking,
+                        Env::IOPriority rate_limiter_priority);
+  FilePrefetchBuffer* prefetch_buffer() { return prefetch_buffer_.get(); }
+
+  void UpdateReadPattern(const uint64_t& offset, const size_t& len) {
+    prev_offset_ = offset;
+    prev_len_ = len;
+  }
+
+  bool IsBlockSequential(const uint64_t& offset) {
+    return (prev_len_ == 0 || (prev_offset_ + prev_len_ == offset));
+  }
+
+  void ResetValues(size_t initial_auto_readahead_size) {
+    num_file_reads_ = 1;
+    // Since initial_auto_readahead_size_ can be different from
+    // the value passed to BlockBasedTableOptions.initial_auto_readahead_size in
+    // case of adaptive_readahead, so fallback the readahead_size_ to that value
+    // in case of reset.
+    initial_auto_readahead_size_ = initial_auto_readahead_size;
+    readahead_size_ = initial_auto_readahead_size_;
+    readahead_limit_ = 0;
+    return;
+  }
+
+  void SetReadaheadState(ReadaheadFileInfo::ReadaheadInfo* readahead_info) {
+    num_file_reads_ = readahead_info->num_file_reads;
+    initial_auto_readahead_size_ = readahead_info->readahead_size;
+    TEST_SYNC_POINT_CALLBACK("BlockPrefetcher::SetReadaheadState",
+                             &initial_auto_readahead_size_);
+  }
+
+ private:
+  // Readahead size used in compaction, its value is used only if
+  // lookup_context_.caller = kCompaction.
+  size_t compaction_readahead_size_;
+
+  // readahead_size_ is used if underlying FS supports prefetching.
+  size_t readahead_size_;
+  size_t readahead_limit_ = 0;
+  // initial_auto_readahead_size_ is used if RocksDB uses internal prefetch
+  // buffer.
+  uint64_t initial_auto_readahead_size_;
+  uint64_t num_file_reads_ = 0;
+  uint64_t prev_offset_ = 0;
+  size_t prev_len_ = 0;
+  std::unique_ptr<FilePrefetchBuffer> prefetch_buffer_;
+};
+}  // namespace ROCKSDB_NAMESPACE