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rocksdb/table/block.h

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14 KiB

// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
// This source code is licensed under the BSD-style license found in the
// LICENSE file in the root directory of this source tree. An additional grant
// of patent rights can be found in the PATENTS file in the same directory.
// This source code is also licensed under the GPLv2 license found in the
// COPYING file in the root directory of this source tree.
//
// 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>
#ifdef ROCKSDB_MALLOC_USABLE_SIZE
#ifdef OS_FREEBSD
#include <malloc_np.h>
#else
#include <malloc.h>
#endif
#endif
#include "db/dbformat.h"
#include "db/pinned_iterators_manager.h"
#include "rocksdb/iterator.h"
#include "rocksdb/options.h"
#include "rocksdb/statistics.h"
#include "table/block_prefix_index.h"
#include "table/internal_iterator.h"
#include "format.h"
namespace rocksdb {
struct BlockContents;
class Comparator;
class BlockIter;
class BlockPrefixIndex;
// BlockReadAmpBitmap is a bitmap that map the rocksdb::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) {
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 >> static_cast<size_t>(bytes_per_bit_pow_)) +
(block_size % (static_cast<size_t>(1)
<< static_cast<size_t>(bytes_per_bit_pow_)) !=
0);
// bitmap_size = ceil(num_bits_needed / kBitsPerEntry)
size_t bitmap_size = (num_bits_needed / kBitsPerEntry) +
(num_bits_needed % kBitsPerEntry != 0);
// Create bitmap and set all the bits to 0
bitmap_ = new std::atomic<uint32_t>[bitmap_size];
memset(bitmap_, 0, bitmap_size * kBytesPersEntry);
RecordTick(GetStatistics(), READ_AMP_TOTAL_READ_BYTES,
num_bits_needed << bytes_per_bit_pow_);
}
~BlockReadAmpBitmap() { delete[] bitmap_; }
void Mark(uint32_t start_offset, uint32_t end_offset) {
assert(end_offset >= start_offset);
// Every new bit we set will bump this counter
uint32_t new_useful_bytes = 0;
// Index of first bit in mask (start_offset / bytes_per_bit)
uint32_t start_bit = start_offset >> bytes_per_bit_pow_;
// Index of last bit in mask (end_offset / bytes_per_bit)
uint32_t end_bit = end_offset >> bytes_per_bit_pow_;
// Index of middle bit (unique to this range)
uint32_t mid_bit = start_bit + 1;
// It's guaranteed that ranges sent to Mark() wont overlap, this mean that
// we dont need to set the middle bits, we can simply set only one bit of
// the middle bits, and check this bit if we want to know if the whole
// range is set or not.
if (mid_bit < end_bit) {
if (GetAndSet(mid_bit) == 0) {
new_useful_bytes += (end_bit - mid_bit) << bytes_per_bit_pow_;
} else {
// If the middle bit is set, it's guaranteed that start and end bits
// are also set
return;
}
} else {
// This range dont have a middle bit, the whole range fall in 1 or 2 bits
}
if (GetAndSet(start_bit) == 0) {
new_useful_bytes += (1 << bytes_per_bit_pow_);
}
if (GetAndSet(end_bit) == 0) {
new_useful_bytes += (1 << bytes_per_bit_pow_);
}
if (new_useful_bytes > 0) {
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_; }
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_;
};
class Block {
public:
// Initialize the block with the specified contents.
explicit Block(BlockContents&& contents, SequenceNumber _global_seqno,
size_t read_amp_bytes_per_bit = 0,
Statistics* statistics = nullptr);
~Block() = default;
size_t size() const { return size_; }
const char* data() const { return data_; }
bool cachable() const { return contents_.cachable; }
size_t usable_size() const {
#ifdef ROCKSDB_MALLOC_USABLE_SIZE
if (contents_.allocation.get() != nullptr) {
return malloc_usable_size(contents_.allocation.get());
}
#endif // ROCKSDB_MALLOC_USABLE_SIZE
return size_;
}
uint32_t NumRestarts() const;
CompressionType compression_type() const {
return contents_.compression_type;
}
// If hash index lookup is enabled and `use_hash_index` is true. This block
// will do hash lookup for the key prefix.
//
// 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.
//
// If iter is null, return new Iterator
// If iter is not null, update this one and return it as Iterator*
//
// If total_order_seek is true, hash_index_ and prefix_index_ are ignored.
// This option only applies for index block. For data block, hash_index_
// and prefix_index_ are null, so this option does not matter.
InternalIterator* NewIterator(const Comparator* comparator,
BlockIter* iter = nullptr,
bool total_order_seek = true,
Statistics* stats = nullptr);
void SetBlockPrefixIndex(BlockPrefixIndex* prefix_index);
// Report an approximation of how much memory has been used.
size_t ApproximateMemoryUsage() const;
SequenceNumber global_seqno() const { return global_seqno_; }
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
std::unique_ptr<BlockPrefixIndex> prefix_index_;
std::unique_ptr<BlockReadAmpBitmap> read_amp_bitmap_;
// All keys in the block will have seqno = global_seqno_, regardless of
// the encoded value (kDisableGlobalSequenceNumber means disabled)
const SequenceNumber global_seqno_;
// No copying allowed
Block(const Block&);
void operator=(const Block&);
};
class BlockIter : public InternalIterator {
public:
BlockIter()
: comparator_(nullptr),
data_(nullptr),
restarts_(0),
num_restarts_(0),
current_(0),
restart_index_(0),
status_(Status::OK()),
prefix_index_(nullptr),
key_pinned_(false),
global_seqno_(kDisableGlobalSequenceNumber),
read_amp_bitmap_(nullptr),
last_bitmap_offset_(0) {}
BlockIter(const Comparator* comparator, const char* data, uint32_t restarts,
uint32_t num_restarts, BlockPrefixIndex* prefix_index,
SequenceNumber global_seqno, BlockReadAmpBitmap* read_amp_bitmap)
: BlockIter() {
Initialize(comparator, data, restarts, num_restarts, prefix_index,
global_seqno, read_amp_bitmap);
}
void Initialize(const Comparator* comparator, const char* data,
uint32_t restarts, uint32_t num_restarts,
BlockPrefixIndex* prefix_index, SequenceNumber global_seqno,
BlockReadAmpBitmap* read_amp_bitmap) {
assert(data_ == nullptr); // Ensure it is called only once
assert(num_restarts > 0); // Ensure the param is valid
comparator_ = comparator;
data_ = data;
restarts_ = restarts;
num_restarts_ = num_restarts;
current_ = restarts_;
restart_index_ = num_restarts_;
prefix_index_ = prefix_index;
global_seqno_ = global_seqno;
read_amp_bitmap_ = read_amp_bitmap;
last_bitmap_offset_ = current_ + 1;
}
void SetStatus(Status s) {
status_ = s;
}
virtual bool Valid() const override { return current_ < restarts_; }
virtual Status status() const override { return status_; }
virtual Slice key() const override {
assert(Valid());
return key_.GetInternalKey();
}
virtual 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_;
}
virtual void Next() override;
virtual void Prev() override;
virtual void Seek(const Slice& target) override;
virtual void SeekForPrev(const Slice& target) override;
virtual void SeekToFirst() override;
virtual void SeekToLast() override;
#ifndef NDEBUG
~BlockIter() {
// Assert that the BlockIter is never deleted while Pinning is Enabled.
assert(!pinned_iters_mgr_ ||
(pinned_iters_mgr_ && !pinned_iters_mgr_->PinningEnabled()));
}
virtual void SetPinnedItersMgr(
PinnedIteratorsManager* pinned_iters_mgr) override {
pinned_iters_mgr_ = pinned_iters_mgr;
}
PinnedIteratorsManager* pinned_iters_mgr_ = nullptr;
#endif
virtual bool IsKeyPinned() const override { return key_pinned_; }
virtual bool IsValuePinned() const override { return true; }
size_t TEST_CurrentEntrySize() { return NextEntryOffset() - current_; }
uint32_t ValueOffset() const {
return static_cast<uint32_t>(value_.data() - data_);
}
private:
const Comparator* comparator_;
const char* data_; // underlying block contents
uint32_t restarts_; // Offset of restart array (list of fixed32)
uint32_t num_restarts_; // Number of uint32_t entries in restart array
// current_ is offset in data_ of current entry. >= restarts_ if !Valid
uint32_t current_;
uint32_t restart_index_; // Index of restart block in which current_ falls
IterKey key_;
Slice value_;
Status status_;
BlockPrefixIndex* prefix_index_;
bool key_pinned_;
SequenceNumber global_seqno_;
// 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;
inline int Compare(const Slice& a, const Slice& b) const {
return comparator_->Compare(a, b);
}
// 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) {
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();
bool ParseNextKey();
bool BinarySeek(const Slice& target, uint32_t left, uint32_t right,
uint32_t* index);
int CompareBlockKey(uint32_t block_index, const Slice& target);
bool BinaryBlockIndexSeek(const Slice& target, uint32_t* block_ids,
uint32_t left, uint32_t right,
uint32_t* index);
bool PrefixSeek(const Slice& target, uint32_t* index);
};
} // namespace rocksdb