1 files changed, 744 insertions, 0 deletions
diff --git a/src/rocksdb/table/block_based/block.h b/src/rocksdb/table/block_based/block.h
new file mode 100644
index 000000000..5d73f72f6
--- /dev/null
+++ b/src/rocksdb/table/block_based/block.h
@@ -0,0 +1,744 @@
+//  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 <stddef.h>
+#include <stdint.h>
+
+#include <string>
+#include <vector>
+
+#include "db/pinned_iterators_manager.h"
+#include "port/malloc.h"
+#include "rocksdb/iterator.h"
+#include "rocksdb/options.h"
+#include "rocksdb/statistics.h"
+#include "rocksdb/table.h"
+#include "table/block_based/block_prefix_index.h"
+#include "table/block_based/data_block_hash_index.h"
+#include "table/format.h"
+#include "table/internal_iterator.h"
+#include "test_util/sync_point.h"
+#include "util/random.h"
+
+namespace ROCKSDB_NAMESPACE {
+
+struct BlockContents;
+class Comparator;
+template <class TValue>
+class BlockIter;
+class DataBlockIter;
+class IndexBlockIter;
+class MetaBlockIter;
+class BlockPrefixIndex;
+
+// BlockReadAmpBitmap is a bitmap that map the ROCKSDB_NAMESPACE::Block data
+// bytes to a bitmap with ratio bytes_per_bit. Whenever we access a range of
+// bytes in the Block we update the bitmap and increment
+// READ_AMP_ESTIMATE_USEFUL_BYTES.
+class BlockReadAmpBitmap {
+ public:
+  explicit BlockReadAmpBitmap(size_t block_size, size_t bytes_per_bit,
+                              Statistics* statistics)
+      : bitmap_(nullptr),
+        bytes_per_bit_pow_(0),
+        statistics_(statistics),
+        rnd_(Random::GetTLSInstance()->Uniform(
+            static_cast<int>(bytes_per_bit))) {
+    TEST_SYNC_POINT_CALLBACK("BlockReadAmpBitmap:rnd", &rnd_);
+    assert(block_size > 0 && bytes_per_bit > 0);
+
+    // convert bytes_per_bit to be a power of 2
+    while (bytes_per_bit >>= 1) {
+      bytes_per_bit_pow_++;
+    }
+
+    // num_bits_needed = ceil(block_size / bytes_per_bit)
+    size_t num_bits_needed = ((block_size - 1) >> bytes_per_bit_pow_) + 1;
+    assert(num_bits_needed > 0);
+
+    // bitmap_size = ceil(num_bits_needed / kBitsPerEntry)
+    size_t bitmap_size = (num_bits_needed - 1) / kBitsPerEntry + 1;
+
+    // Create bitmap and set all the bits to 0
+    bitmap_ = new std::atomic<uint32_t>[bitmap_size]();
+
+    RecordTick(GetStatistics(), READ_AMP_TOTAL_READ_BYTES, block_size);
+  }
+
+  ~BlockReadAmpBitmap() { delete[] bitmap_; }
+
+  void Mark(uint32_t start_offset, uint32_t end_offset) {
+    assert(end_offset >= start_offset);
+    // Index of first bit in mask
+    uint32_t start_bit =
+        (start_offset + (1 << bytes_per_bit_pow_) - rnd_ - 1) >>
+        bytes_per_bit_pow_;
+    // Index of last bit in mask + 1
+    uint32_t exclusive_end_bit =
+        (end_offset + (1 << bytes_per_bit_pow_) - rnd_) >> bytes_per_bit_pow_;
+    if (start_bit >= exclusive_end_bit) {
+      return;
+    }
+    assert(exclusive_end_bit > 0);
+
+    if (GetAndSet(start_bit) == 0) {
+      uint32_t new_useful_bytes = (exclusive_end_bit - start_bit)
+                                  << bytes_per_bit_pow_;
+      RecordTick(GetStatistics(), READ_AMP_ESTIMATE_USEFUL_BYTES,
+                 new_useful_bytes);
+    }
+  }
+
+  Statistics* GetStatistics() {
+    return statistics_.load(std::memory_order_relaxed);
+  }
+
+  void SetStatistics(Statistics* stats) { statistics_.store(stats); }
+
+  uint32_t GetBytesPerBit() { return 1 << bytes_per_bit_pow_; }
+
+  size_t ApproximateMemoryUsage() const {
+#ifdef ROCKSDB_MALLOC_USABLE_SIZE
+    return malloc_usable_size((void*)this);
+#endif  // ROCKSDB_MALLOC_USABLE_SIZE
+    return sizeof(*this);
+  }
+
+ private:
+  // Get the current value of bit at `bit_idx` and set it to 1
+  inline bool GetAndSet(uint32_t bit_idx) {
+    const uint32_t byte_idx = bit_idx / kBitsPerEntry;
+    const uint32_t bit_mask = 1 << (bit_idx % kBitsPerEntry);
+
+    return bitmap_[byte_idx].fetch_or(bit_mask, std::memory_order_relaxed) &
+           bit_mask;
+  }
+
+  const uint32_t kBytesPersEntry = sizeof(uint32_t);   // 4 bytes
+  const uint32_t kBitsPerEntry = kBytesPersEntry * 8;  // 32 bits
+
+  // Bitmap used to record the bytes that we read, use atomic to protect
+  // against multiple threads updating the same bit
+  std::atomic<uint32_t>* bitmap_;
+  // (1 << bytes_per_bit_pow_) is bytes_per_bit. Use power of 2 to optimize
+  // muliplication and division
+  uint8_t bytes_per_bit_pow_;
+  // Pointer to DB Statistics object, Since this bitmap may outlive the DB
+  // this pointer maybe invalid, but the DB will update it to a valid pointer
+  // by using SetStatistics() before calling Mark()
+  std::atomic<Statistics*> statistics_;
+  uint32_t rnd_;
+};
+
+// class Block is the uncompressed and "parsed" form for blocks containing
+// key-value pairs. (See BlockContents comments for more on terminology.)
+// This includes the in-memory representation of data blocks, index blocks
+// (including partitions), range deletion blocks, properties blocks, metaindex
+// blocks, as well as the top level of the partitioned filter structure (which
+// is actually an index of the filter partitions). It is NOT suitable for
+// compressed blocks in general, filter blocks/partitions, or compression
+// dictionaries.
+//
+// See https://github.com/facebook/rocksdb/wiki/Rocksdb-BlockBasedTable-Format
+// for details of the format and the various block types.
+//
+// TODO: Rename to ParsedKvBlock?
+class Block {
+ public:
+  // Initialize the block with the specified contents.
+  explicit Block(BlockContents&& contents, size_t read_amp_bytes_per_bit = 0,
+                 Statistics* statistics = nullptr);
+  // No copying allowed
+  Block(const Block&) = delete;
+  void operator=(const Block&) = delete;
+
+  ~Block();
+
+  size_t size() const { return size_; }
+  const char* data() const { return data_; }
+  // The additional memory space taken by the block data.
+  size_t usable_size() const { return contents_.usable_size(); }
+  uint32_t NumRestarts() const;
+  bool own_bytes() const { return contents_.own_bytes(); }
+
+  BlockBasedTableOptions::DataBlockIndexType IndexType() const;
+
+  // raw_ucmp is a raw (i.e., not wrapped by `UserComparatorWrapper`) user key
+  // comparator.
+  //
+  // If iter is null, return new Iterator
+  // If iter is not null, update this one and return it as Iterator*
+  //
+  // Updates read_amp_bitmap_ if it is not nullptr.
+  //
+  // If `block_contents_pinned` is true, the caller will guarantee that when
+  // the cleanup functions are transferred from the iterator to other
+  // classes, e.g. PinnableSlice, the pointer to the bytes will still be
+  // valid. Either the iterator holds cache handle or ownership of some resource
+  // and release them in a release function, or caller is sure that the data
+  // will not go away (for example, it's from mmapped file which will not be
+  // closed).
+  //
+  // NOTE: for the hash based lookup, if a key prefix doesn't match any key,
+  // the iterator will simply be set as "invalid", rather than returning
+  // the key that is just pass the target key.
+  DataBlockIter* NewDataIterator(const Comparator* raw_ucmp,
+                                 SequenceNumber global_seqno,
+                                 DataBlockIter* iter = nullptr,
+                                 Statistics* stats = nullptr,
+                                 bool block_contents_pinned = false);
+
+  // Returns an MetaBlockIter for iterating over blocks containing metadata
+  // (like Properties blocks).  Unlike data blocks, the keys for these blocks
+  // do not contain sequence numbers, do not use a user-define comparator, and
+  // do not track read amplification/statistics.  Additionally, MetaBlocks will
+  // not assert if the block is formatted improperly.
+  //
+  // If `block_contents_pinned` is true, the caller will guarantee that when
+  // the cleanup functions are transferred from the iterator to other
+  // classes, e.g. PinnableSlice, the pointer to the bytes will still be
+  // valid. Either the iterator holds cache handle or ownership of some resource
+  // and release them in a release function, or caller is sure that the data
+  // will not go away (for example, it's from mmapped file which will not be
+  // closed).
+  MetaBlockIter* NewMetaIterator(bool block_contents_pinned = false);
+
+  // raw_ucmp is a raw (i.e., not wrapped by `UserComparatorWrapper`) user key
+  // comparator.
+  //
+  // key_includes_seq, default true, means that the keys are in internal key
+  // format.
+  // value_is_full, default true, means that no delta encoding is
+  // applied to values.
+  //
+  // If `prefix_index` is not nullptr this block will do hash lookup for the key
+  // prefix. If total_order_seek is true, prefix_index_ is ignored.
+  //
+  // `have_first_key` controls whether IndexValue will contain
+  // first_internal_key. It affects data serialization format, so the same value
+  // have_first_key must be used when writing and reading index.
+  // It is determined by IndexType property of the table.
+  IndexBlockIter* NewIndexIterator(const Comparator* raw_ucmp,
+                                   SequenceNumber global_seqno,
+                                   IndexBlockIter* iter, Statistics* stats,
+                                   bool total_order_seek, bool have_first_key,
+                                   bool key_includes_seq, bool value_is_full,
+                                   bool block_contents_pinned = false,
+                                   BlockPrefixIndex* prefix_index = nullptr);
+
+  // Report an approximation of how much memory has been used.
+  size_t ApproximateMemoryUsage() const;
+
+ private:
+  BlockContents contents_;
+  const char* data_;         // contents_.data.data()
+  size_t size_;              // contents_.data.size()
+  uint32_t restart_offset_;  // Offset in data_ of restart array
+  uint32_t num_restarts_;
+  std::unique_ptr<BlockReadAmpBitmap> read_amp_bitmap_;
+  DataBlockHashIndex data_block_hash_index_;
+};
+
+// A `BlockIter` iterates over the entries in a `Block`'s data buffer. The
+// format of this data buffer is an uncompressed, sorted sequence of key-value
+// pairs (see `Block` API for more details).
+//
+// Notably, the keys may either be in internal key format or user key format.
+// Subclasses are responsible for configuring the key format.
+//
+// `BlockIter` intends to provide final overrides for all of
+// `InternalIteratorBase` functions that can move the iterator. It does
+// this to guarantee `UpdateKey()` is called exactly once after each key
+// movement potentially visible to users. In this step, the key is prepared
+// (e.g., serialized if global seqno is in effect) so it can be returned
+// immediately when the user asks for it via calling `key() const`.
+//
+// For its subclasses, it provides protected variants of the above-mentioned
+// final-overridden methods. They are named with the "Impl" suffix, e.g.,
+// `Seek()` logic would be implemented by subclasses in `SeekImpl()`. These
+// "Impl" functions are responsible for positioning `raw_key_` but not
+// invoking `UpdateKey()`.
+template <class TValue>
+class BlockIter : public InternalIteratorBase<TValue> {
+ public:
+  // Makes Valid() return false, status() return `s`, and Seek()/Prev()/etc do
+  // nothing. Calls cleanup functions.
+  virtual void Invalidate(const Status& s) {
+    // Assert that the BlockIter is never deleted while Pinning is Enabled.
+    assert(!pinned_iters_mgr_ || !pinned_iters_mgr_->PinningEnabled());
+
+    data_ = nullptr;
+    current_ = restarts_;
+    status_ = s;
+
+    // Call cleanup callbacks.
+    Cleanable::Reset();
+  }
+
+  bool Valid() const override { return current_ < restarts_; }
+
+  virtual void SeekToFirst() override final {
+    SeekToFirstImpl();
+    UpdateKey();
+  }
+
+  virtual void SeekToLast() override final {
+    SeekToLastImpl();
+    UpdateKey();
+  }
+
+  virtual void Seek(const Slice& target) override final {
+    SeekImpl(target);
+    UpdateKey();
+  }
+
+  virtual void SeekForPrev(const Slice& target) override final {
+    SeekForPrevImpl(target);
+    UpdateKey();
+  }
+
+  virtual void Next() override final {
+    NextImpl();
+    UpdateKey();
+  }
+
+  virtual bool NextAndGetResult(IterateResult* result) override final {
+    // This does not need to call `UpdateKey()` as the parent class only has
+    // access to the `UpdateKey()`-invoking functions.
+    return InternalIteratorBase<TValue>::NextAndGetResult(result);
+  }
+
+  virtual void Prev() override final {
+    PrevImpl();
+    UpdateKey();
+  }
+
+  Status status() const override { return status_; }
+  Slice key() const override {
+    assert(Valid());
+    return key_;
+  }
+
+#ifndef NDEBUG
+  ~BlockIter() override {
+    // Assert that the BlockIter is never deleted while Pinning is Enabled.
+    assert(!pinned_iters_mgr_ ||
+           (pinned_iters_mgr_ && !pinned_iters_mgr_->PinningEnabled()));
+    status_.PermitUncheckedError();
+  }
+  void SetPinnedItersMgr(PinnedIteratorsManager* pinned_iters_mgr) override {
+    pinned_iters_mgr_ = pinned_iters_mgr;
+  }
+  PinnedIteratorsManager* pinned_iters_mgr_ = nullptr;
+#endif
+
+  bool IsKeyPinned() const override {
+    return block_contents_pinned_ && key_pinned_;
+  }
+
+  bool IsValuePinned() const override { return block_contents_pinned_; }
+
+  size_t TEST_CurrentEntrySize() { return NextEntryOffset() - current_; }
+
+  uint32_t ValueOffset() const {
+    return static_cast<uint32_t>(value_.data() - data_);
+  }
+
+  void SetCacheHandle(Cache::Handle* handle) { cache_handle_ = handle; }
+
+  Cache::Handle* cache_handle() { return cache_handle_; }
+
+ protected:
+  std::unique_ptr<InternalKeyComparator> icmp_;
+  const char* data_;       // underlying block contents
+  uint32_t num_restarts_;  // Number of uint32_t entries in restart array
+
+  // Index of restart block in which current_ or current_-1 falls
+  uint32_t restart_index_;
+  uint32_t restarts_;  // Offset of restart array (list of fixed32)
+  // current_ is offset in data_ of current entry.  >= restarts_ if !Valid
+  uint32_t current_;
+  // Raw key from block.
+  IterKey raw_key_;
+  // Buffer for key data when global seqno assignment is enabled.
+  IterKey key_buf_;
+  Slice value_;
+  Status status_;
+  // Key to be exposed to users.
+  Slice key_;
+  bool key_pinned_;
+  // Whether the block data is guaranteed to outlive this iterator, and
+  // as long as the cleanup functions are transferred to another class,
+  // e.g. PinnableSlice, the pointer to the bytes will still be valid.
+  bool block_contents_pinned_;
+  SequenceNumber global_seqno_;
+
+  virtual void SeekToFirstImpl() = 0;
+  virtual void SeekToLastImpl() = 0;
+  virtual void SeekImpl(const Slice& target) = 0;
+  virtual void SeekForPrevImpl(const Slice& target) = 0;
+  virtual void NextImpl() = 0;
+
+  virtual void PrevImpl() = 0;
+
+  template <typename DecodeEntryFunc>
+  inline bool ParseNextKey(bool* is_shared);
+
+  void InitializeBase(const Comparator* raw_ucmp, const char* data,
+                      uint32_t restarts, uint32_t num_restarts,
+                      SequenceNumber global_seqno, bool block_contents_pinned) {
+    assert(data_ == nullptr);  // Ensure it is called only once
+    assert(num_restarts > 0);  // Ensure the param is valid
+
+    icmp_ = std::make_unique<InternalKeyComparator>(raw_ucmp);
+    data_ = data;
+    restarts_ = restarts;
+    num_restarts_ = num_restarts;
+    current_ = restarts_;
+    restart_index_ = num_restarts_;
+    global_seqno_ = global_seqno;
+    block_contents_pinned_ = block_contents_pinned;
+    cache_handle_ = nullptr;
+  }
+
+  // Must be called every time a key is found that needs to be returned to user,
+  // and may be called when no key is found (as a no-op). Updates `key_`,
+  // `key_buf_`, and `key_pinned_` with info about the found key.
+  void UpdateKey() {
+    key_buf_.Clear();
+    if (!Valid()) {
+      return;
+    }
+    if (raw_key_.IsUserKey()) {
+      assert(global_seqno_ == kDisableGlobalSequenceNumber);
+      key_ = raw_key_.GetUserKey();
+      key_pinned_ = raw_key_.IsKeyPinned();
+    } else if (global_seqno_ == kDisableGlobalSequenceNumber) {
+      key_ = raw_key_.GetInternalKey();
+      key_pinned_ = raw_key_.IsKeyPinned();
+    } else {
+      key_buf_.SetInternalKey(raw_key_.GetUserKey(), global_seqno_,
+                              ExtractValueType(raw_key_.GetInternalKey()));
+      key_ = key_buf_.GetInternalKey();
+      key_pinned_ = false;
+    }
+  }
+
+  // Returns the result of `Comparator::Compare()`, where the appropriate
+  // comparator is used for the block contents, the LHS argument is the current
+  // key with global seqno applied, and the RHS argument is `other`.
+  int CompareCurrentKey(const Slice& other) {
+    if (raw_key_.IsUserKey()) {
+      assert(global_seqno_ == kDisableGlobalSequenceNumber);
+      return icmp_->user_comparator()->Compare(raw_key_.GetUserKey(), other);
+    } else if (global_seqno_ == kDisableGlobalSequenceNumber) {
+      return icmp_->Compare(raw_key_.GetInternalKey(), other);
+    }
+    return icmp_->Compare(raw_key_.GetInternalKey(), global_seqno_, other,
+                          kDisableGlobalSequenceNumber);
+  }
+
+ private:
+  // Store the cache handle, if the block is cached. We need this since the
+  // only other place the handle is stored is as an argument to the Cleanable
+  // function callback, which is hard to retrieve. When multiple value
+  // PinnableSlices reference the block, they need the cache handle in order
+  // to bump up the ref count
+  Cache::Handle* cache_handle_;
+
+ public:
+  // Return the offset in data_ just past the end of the current entry.
+  inline uint32_t NextEntryOffset() const {
+    // NOTE: We don't support blocks bigger than 2GB
+    return static_cast<uint32_t>((value_.data() + value_.size()) - data_);
+  }
+
+  uint32_t GetRestartPoint(uint32_t index) {
+    assert(index < num_restarts_);
+    return DecodeFixed32(data_ + restarts_ + index * sizeof(uint32_t));
+  }
+
+  void SeekToRestartPoint(uint32_t index) {
+    raw_key_.Clear();
+    restart_index_ = index;
+    // current_ will be fixed by ParseNextKey();
+
+    // ParseNextKey() starts at the end of value_, so set value_ accordingly
+    uint32_t offset = GetRestartPoint(index);
+    value_ = Slice(data_ + offset, 0);
+  }
+
+  void CorruptionError();
+
+ protected:
+  template <typename DecodeKeyFunc>
+  inline bool BinarySeek(const Slice& target, uint32_t* index,
+                         bool* is_index_key_result);
+
+  void FindKeyAfterBinarySeek(const Slice& target, uint32_t index,
+                              bool is_index_key_result);
+};
+
+class DataBlockIter final : public BlockIter<Slice> {
+ public:
+  DataBlockIter()
+      : BlockIter(), read_amp_bitmap_(nullptr), last_bitmap_offset_(0) {}
+  DataBlockIter(const Comparator* raw_ucmp, const char* data, uint32_t restarts,
+                uint32_t num_restarts, SequenceNumber global_seqno,
+                BlockReadAmpBitmap* read_amp_bitmap, bool block_contents_pinned,
+                DataBlockHashIndex* data_block_hash_index)
+      : DataBlockIter() {
+    Initialize(raw_ucmp, data, restarts, num_restarts, global_seqno,
+               read_amp_bitmap, block_contents_pinned, data_block_hash_index);
+  }
+  void Initialize(const Comparator* raw_ucmp, const char* data,
+                  uint32_t restarts, uint32_t num_restarts,
+                  SequenceNumber global_seqno,
+                  BlockReadAmpBitmap* read_amp_bitmap,
+                  bool block_contents_pinned,
+                  DataBlockHashIndex* data_block_hash_index) {
+    InitializeBase(raw_ucmp, data, restarts, num_restarts, global_seqno,
+                   block_contents_pinned);
+    raw_key_.SetIsUserKey(false);
+    read_amp_bitmap_ = read_amp_bitmap;
+    last_bitmap_offset_ = current_ + 1;
+    data_block_hash_index_ = data_block_hash_index;
+  }
+
+  Slice value() const override {
+    assert(Valid());
+    if (read_amp_bitmap_ && current_ < restarts_ &&
+        current_ != last_bitmap_offset_) {
+      read_amp_bitmap_->Mark(current_ /* current entry offset */,
+                             NextEntryOffset() - 1);
+      last_bitmap_offset_ = current_;
+    }
+    return value_;
+  }
+
+  inline bool SeekForGet(const Slice& target) {
+    if (!data_block_hash_index_) {
+      SeekImpl(target);
+      UpdateKey();
+      return true;
+    }
+    bool res = SeekForGetImpl(target);
+    UpdateKey();
+    return res;
+  }
+
+  void Invalidate(const Status& s) override {
+    BlockIter::Invalidate(s);
+    // Clear prev entries cache.
+    prev_entries_keys_buff_.clear();
+    prev_entries_.clear();
+    prev_entries_idx_ = -1;
+  }
+
+ protected:
+  friend Block;
+  inline bool ParseNextDataKey(bool* is_shared);
+  void SeekToFirstImpl() override;
+  void SeekToLastImpl() override;
+  void SeekImpl(const Slice& target) override;
+  void SeekForPrevImpl(const Slice& target) override;
+  void NextImpl() override;
+  void PrevImpl() override;
+
+ private:
+  // read-amp bitmap
+  BlockReadAmpBitmap* read_amp_bitmap_;
+  // last `current_` value we report to read-amp bitmp
+  mutable uint32_t last_bitmap_offset_;
+  struct CachedPrevEntry {
+    explicit CachedPrevEntry(uint32_t _offset, const char* _key_ptr,
+                             size_t _key_offset, size_t _key_size, Slice _value)
+        : offset(_offset),
+          key_ptr(_key_ptr),
+          key_offset(_key_offset),
+          key_size(_key_size),
+          value(_value) {}
+
+    // offset of entry in block
+    uint32_t offset;
+    // Pointer to key data in block (nullptr if key is delta-encoded)
+    const char* key_ptr;
+    // offset of key in prev_entries_keys_buff_ (0 if key_ptr is not nullptr)
+    size_t key_offset;
+    // size of key
+    size_t key_size;
+    // value slice pointing to data in block
+    Slice value;
+  };
+  std::string prev_entries_keys_buff_;
+  std::vector<CachedPrevEntry> prev_entries_;
+  int32_t prev_entries_idx_ = -1;
+
+  DataBlockHashIndex* data_block_hash_index_;
+
+  bool SeekForGetImpl(const Slice& target);
+};
+
+// Iterator over MetaBlocks.  MetaBlocks are similar to Data Blocks and
+// are used to store Properties associated with table.
+// Meta blocks always store user keys (no sequence number) and always
+// use the BytewiseComparator.  Additionally, MetaBlock accesses are
+// not recorded in the Statistics or for Read-Amplification.
+class MetaBlockIter final : public BlockIter<Slice> {
+ public:
+  MetaBlockIter() : BlockIter() { raw_key_.SetIsUserKey(true); }
+  void Initialize(const char* data, uint32_t restarts, uint32_t num_restarts,
+                  bool block_contents_pinned) {
+    // Initializes the iterator with a BytewiseComparator and
+    // the raw key being a user key.
+    InitializeBase(BytewiseComparator(), data, restarts, num_restarts,
+                   kDisableGlobalSequenceNumber, block_contents_pinned);
+    raw_key_.SetIsUserKey(true);
+  }
+
+  Slice value() const override {
+    assert(Valid());
+    return value_;
+  }
+
+ protected:
+  void SeekToFirstImpl() override;
+  void SeekToLastImpl() override;
+  void SeekImpl(const Slice& target) override;
+  void SeekForPrevImpl(const Slice& target) override;
+  void NextImpl() override;
+  void PrevImpl() override;
+};
+
+class IndexBlockIter final : public BlockIter<IndexValue> {
+ public:
+  IndexBlockIter() : BlockIter(), prefix_index_(nullptr) {}
+
+  // key_includes_seq, default true, means that the keys are in internal key
+  // format.
+  // value_is_full, default true, means that no delta encoding is
+  // applied to values.
+  void Initialize(const Comparator* raw_ucmp, const char* data,
+                  uint32_t restarts, uint32_t num_restarts,
+                  SequenceNumber global_seqno, BlockPrefixIndex* prefix_index,
+                  bool have_first_key, bool key_includes_seq,
+                  bool value_is_full, bool block_contents_pinned) {
+    InitializeBase(raw_ucmp, data, restarts, num_restarts,
+                   kDisableGlobalSequenceNumber, block_contents_pinned);
+    raw_key_.SetIsUserKey(!key_includes_seq);
+    prefix_index_ = prefix_index;
+    value_delta_encoded_ = !value_is_full;
+    have_first_key_ = have_first_key;
+    if (have_first_key_ && global_seqno != kDisableGlobalSequenceNumber) {
+      global_seqno_state_.reset(new GlobalSeqnoState(global_seqno));
+    } else {
+      global_seqno_state_.reset();
+    }
+  }
+
+  Slice user_key() const override {
+    assert(Valid());
+    return raw_key_.GetUserKey();
+  }
+
+  IndexValue value() const override {
+    assert(Valid());
+    if (value_delta_encoded_ || global_seqno_state_ != nullptr) {
+      return decoded_value_;
+    } else {
+      IndexValue entry;
+      Slice v = value_;
+      Status decode_s __attribute__((__unused__)) =
+          entry.DecodeFrom(&v, have_first_key_, nullptr);
+      assert(decode_s.ok());
+      return entry;
+    }
+  }
+
+  bool IsValuePinned() const override {
+    return global_seqno_state_ != nullptr ? false : BlockIter::IsValuePinned();
+  }
+
+ protected:
+  // IndexBlockIter follows a different contract for prefix iterator
+  // from data iterators.
+  // If prefix of the seek key `target` exists in the file, it must
+  // return the same result as total order seek.
+  // If the prefix of `target` doesn't exist in the file, it can either
+  // return the result of total order seek, or set both of Valid() = false
+  // and status() = NotFound().
+  void SeekImpl(const Slice& target) override;
+
+  void SeekForPrevImpl(const Slice&) override {
+    assert(false);
+    current_ = restarts_;
+    restart_index_ = num_restarts_;
+    status_ = Status::InvalidArgument(
+        "RocksDB internal error: should never call SeekForPrev() on index "
+        "blocks");
+    raw_key_.Clear();
+    value_.clear();
+  }
+
+  void PrevImpl() override;
+
+  void NextImpl() override;
+
+  void SeekToFirstImpl() override;
+
+  void SeekToLastImpl() override;
+
+ private:
+  bool value_delta_encoded_;
+  bool have_first_key_;  // value includes first_internal_key
+  BlockPrefixIndex* prefix_index_;
+  // Whether the value is delta encoded. In that case the value is assumed to be
+  // BlockHandle. The first value in each restart interval is the full encoded
+  // BlockHandle; the restart of encoded size part of the BlockHandle. The
+  // offset of delta encoded BlockHandles is computed by adding the size of
+  // previous delta encoded values in the same restart interval to the offset of
+  // the first value in that restart interval.
+  IndexValue decoded_value_;
+
+  // When sequence number overwriting is enabled, this struct contains the seqno
+  // to overwrite with, and current first_internal_key with overwritten seqno.
+  // This is rarely used, so we put it behind a pointer and only allocate when
+  // needed.
+  struct GlobalSeqnoState {
+    // First internal key according to current index entry, but with sequence
+    // number overwritten to global_seqno.
+    IterKey first_internal_key;
+    SequenceNumber global_seqno;
+
+    explicit GlobalSeqnoState(SequenceNumber seqno) : global_seqno(seqno) {}
+  };
+
+  std::unique_ptr<GlobalSeqnoState> global_seqno_state_;
+
+  // Set *prefix_may_exist to false if no key possibly share the same prefix
+  // as `target`. If not set, the result position should be the same as total
+  // order Seek.
+  bool PrefixSeek(const Slice& target, uint32_t* index, bool* prefix_may_exist);
+  // Set *prefix_may_exist to false if no key can possibly share the same
+  // prefix as `target`. If not set, the result position should be the same
+  // as total order seek.
+  bool BinaryBlockIndexSeek(const Slice& target, uint32_t* block_ids,
+                            uint32_t left, uint32_t right, uint32_t* index,
+                            bool* prefix_may_exist);
+  inline int CompareBlockKey(uint32_t block_index, const Slice& target);
+
+  inline bool ParseNextIndexKey();
+
+  // When value_delta_encoded_ is enabled it decodes the value which is assumed
+  // to be BlockHandle and put it to decoded_value_
+  inline void DecodeCurrentValue(bool is_shared);
+};
+
+}  // namespace ROCKSDB_NAMESPACE