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rocksdb/table/block_based/block.h

748 lines
27 KiB

// 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_;
};
// This Block class is not for any old block: it is designed to hold only
// uncompressed blocks containing sorted key-value pairs. It is thus
// suitable for storing uncompressed 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 (since the latter do not contain sorted key-value pairs).
// Use BlockContents directly for those.
//
// See https://github.com/facebook/rocksdb/wiki/Rocksdb-BlockBasedTable-Format
// for details of the format and the various block types.
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:
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
raw_ucmp_ = 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;
}
// 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:
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);
InternalKeyComparator icmp() {
return InternalKeyComparator(raw_ucmp_, false /* named */);
}
UserComparatorWrapper ucmp() { return UserComparatorWrapper(raw_ucmp_); }
// 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 ucmp().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:
const Comparator* raw_ucmp_;
// 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