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rocksdb/table/filter_block.cc

187 lines
6.1 KiB

// Copyright (c) 2013, 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.
//
// Copyright (c) 2012 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.
#include "table/filter_block.h"
#include "db/dbformat.h"
#include "rocksdb/filter_policy.h"
#include "util/coding.h"
namespace rocksdb {
// See doc/table_format.txt for an explanation of the filter block format.
// Generate new filter every 2KB of data
static const size_t kFilterBaseLg = 11;
static const size_t kFilterBase = 1 << kFilterBaseLg;
FilterBlockBuilder::FilterBlockBuilder(const SliceTransform* prefix_extractor,
const BlockBasedTableOptions& table_opt,
const Comparator* internal_comparator)
: policy_(table_opt.filter_policy.get()),
prefix_extractor_(prefix_extractor),
whole_key_filtering_(table_opt.whole_key_filtering),
comparator_(internal_comparator) {}
void FilterBlockBuilder::StartBlock(uint64_t block_offset) {
uint64_t filter_index = (block_offset / kFilterBase);
assert(filter_index >= filter_offsets_.size());
while (filter_index > filter_offsets_.size()) {
GenerateFilter();
}
}
bool FilterBlockBuilder::SamePrefix(const Slice &key1,
const Slice &key2) const {
if (!prefix_extractor_->InDomain(key1) &&
!prefix_extractor_->InDomain(key2)) {
return true;
} else if (!prefix_extractor_->InDomain(key1) ||
!prefix_extractor_->InDomain(key2)) {
return false;
} else {
return (prefix_extractor_->Transform(key1) ==
prefix_extractor_->Transform(key2));
}
}
void FilterBlockBuilder::AddKey(const Slice& key) {
// get slice for most recently added entry
Slice prev;
size_t added_to_start = 0;
// add key to filter if needed
if (whole_key_filtering_) {
start_.push_back(entries_.size());
++added_to_start;
entries_.append(key.data(), key.size());
}
if (start_.size() > added_to_start) {
size_t prev_start = start_[start_.size() - 1 - added_to_start];
const char* base = entries_.data() + prev_start;
size_t length = entries_.size() - prev_start;
prev = Slice(base, length);
}
// add prefix to filter if needed
if (prefix_extractor_ && prefix_extractor_->InDomain(key)) {
// this assumes prefix(prefix(key)) == prefix(key), as the last
// entry in entries_ may be either a key or prefix, and we use
// prefix(last entry) to get the prefix of the last key.
if (prev.size() == 0 || !SamePrefix(key, prev)) {
Slice prefix = prefix_extractor_->Transform(key);
start_.push_back(entries_.size());
entries_.append(prefix.data(), prefix.size());
}
}
}
Slice FilterBlockBuilder::Finish() {
if (!start_.empty()) {
GenerateFilter();
}
// Append array of per-filter offsets
const uint32_t array_offset = result_.size();
for (size_t i = 0; i < filter_offsets_.size(); i++) {
PutFixed32(&result_, filter_offsets_[i]);
}
PutFixed32(&result_, array_offset);
result_.push_back(kFilterBaseLg); // Save encoding parameter in result
return Slice(result_);
}
void FilterBlockBuilder::GenerateFilter() {
const size_t num_entries = start_.size();
if (num_entries == 0) {
// Fast path if there are no keys for this filter
filter_offsets_.push_back(result_.size());
return;
}
// Make list of keys from flattened key structure
start_.push_back(entries_.size()); // Simplify length computation
tmp_entries_.resize(num_entries);
for (size_t i = 0; i < num_entries; i++) {
const char* base = entries_.data() + start_[i];
size_t length = start_[i+1] - start_[i];
tmp_entries_[i] = Slice(base, length);
}
// Generate filter for current set of keys and append to result_.
filter_offsets_.push_back(result_.size());
policy_->CreateFilter(&tmp_entries_[0], num_entries, &result_);
tmp_entries_.clear();
entries_.clear();
start_.clear();
}
FilterBlockReader::FilterBlockReader(
const SliceTransform* prefix_extractor,
const BlockBasedTableOptions& table_opt,
const Slice& contents, bool delete_contents_after_use)
: policy_(table_opt.filter_policy.get()),
prefix_extractor_(prefix_extractor),
whole_key_filtering_(table_opt.whole_key_filtering),
data_(nullptr),
offset_(nullptr),
num_(0),
base_lg_(0) {
size_t n = contents.size();
if (n < 5) return; // 1 byte for base_lg_ and 4 for start of offset array
base_lg_ = contents[n-1];
uint32_t last_word = DecodeFixed32(contents.data() + n - 5);
if (last_word > n - 5) return;
data_ = contents.data();
offset_ = data_ + last_word;
num_ = (n - 5 - last_word) / 4;
if (delete_contents_after_use) {
filter_data.reset(contents.data());
}
}
bool FilterBlockReader::KeyMayMatch(uint64_t block_offset,
const Slice& key) {
if (!whole_key_filtering_) {
return true;
}
return MayMatch(block_offset, key);
}
bool FilterBlockReader::PrefixMayMatch(uint64_t block_offset,
const Slice& prefix) {
if (!prefix_extractor_) {
return true;
}
return MayMatch(block_offset, prefix);
}
bool FilterBlockReader::MayMatch(uint64_t block_offset, const Slice& entry) {
uint64_t index = block_offset >> base_lg_;
if (index < num_) {
uint32_t start = DecodeFixed32(offset_ + index*4);
uint32_t limit = DecodeFixed32(offset_ + index*4 + 4);
if (start <= limit && limit <= (uint32_t)(offset_ - data_)) {
Slice filter = Slice(data_ + start, limit - start);
return policy_->KeyMayMatch(entry, filter);
} else if (start == limit) {
// Empty filters do not match any entries
return false;
}
}
return true; // Errors are treated as potential matches
}
size_t FilterBlockReader::ApproximateMemoryUsage() const {
return num_ * 4 + 5 + (offset_ - data_);
}
}