112 lines
3.3 KiB
C++
112 lines
3.3 KiB
C++
// Copyright (c) 2012 The LevelDB Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file. See the AUTHORS file for names of contributors.
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#include "table/filter_block.h"
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#include "leveldb/filter_policy.h"
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#include "util/coding.h"
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namespace leveldb {
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// See doc/table_format.md for an explanation of the filter block format.
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// Generate new filter every 2KB of data
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static const size_t kFilterBaseLg = 11;
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static const size_t kFilterBase = 1 << kFilterBaseLg;
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FilterBlockBuilder::FilterBlockBuilder(const FilterPolicy* policy)
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: policy_(policy) {
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}
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void FilterBlockBuilder::StartBlock(uint64_t block_offset) {
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uint64_t filter_index = (block_offset / kFilterBase);
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assert(filter_index >= filter_offsets_.size());
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while (filter_index > filter_offsets_.size()) {
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GenerateFilter();
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}
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}
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void FilterBlockBuilder::AddKey(const Slice& key) {
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Slice k = key;
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start_.push_back(keys_.size());
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keys_.append(k.data(), k.size());
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}
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Slice FilterBlockBuilder::Finish() {
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if (!start_.empty()) {
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GenerateFilter();
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}
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// Append array of per-filter offsets
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const uint32_t array_offset = result_.size();
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for (size_t i = 0; i < filter_offsets_.size(); i++) {
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PutFixed32(&result_, filter_offsets_[i]);
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}
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PutFixed32(&result_, array_offset);
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result_.push_back(kFilterBaseLg); // Save encoding parameter in result
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return Slice(result_);
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}
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void FilterBlockBuilder::GenerateFilter() {
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const size_t num_keys = start_.size();
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if (num_keys == 0) {
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// Fast path if there are no keys for this filter
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filter_offsets_.push_back(result_.size());
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return;
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}
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// Make list of keys from flattened key structure
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start_.push_back(keys_.size()); // Simplify length computation
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tmp_keys_.resize(num_keys);
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for (size_t i = 0; i < num_keys; i++) {
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const char* base = keys_.data() + start_[i];
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size_t length = start_[i+1] - start_[i];
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tmp_keys_[i] = Slice(base, length);
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}
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// Generate filter for current set of keys and append to result_.
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filter_offsets_.push_back(result_.size());
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policy_->CreateFilter(&tmp_keys_[0], static_cast<int>(num_keys), &result_);
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tmp_keys_.clear();
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keys_.clear();
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start_.clear();
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}
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FilterBlockReader::FilterBlockReader(const FilterPolicy* policy,
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const Slice& contents)
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: policy_(policy),
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data_(nullptr),
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offset_(nullptr),
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num_(0),
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base_lg_(0) {
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size_t n = contents.size();
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if (n < 5) return; // 1 byte for base_lg_ and 4 for start of offset array
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base_lg_ = contents[n-1];
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uint32_t last_word = DecodeFixed32(contents.data() + n - 5);
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if (last_word > n - 5) return;
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data_ = contents.data();
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offset_ = data_ + last_word;
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num_ = (n - 5 - last_word) / 4;
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}
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bool FilterBlockReader::KeyMayMatch(uint64_t block_offset, const Slice& key) {
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uint64_t index = block_offset >> base_lg_;
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if (index < num_) {
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uint32_t start = DecodeFixed32(offset_ + index*4);
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uint32_t limit = DecodeFixed32(offset_ + index*4 + 4);
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if (start <= limit && limit <= static_cast<size_t>(offset_ - data_)) {
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Slice filter = Slice(data_ + start, limit - start);
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return policy_->KeyMayMatch(key, filter);
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} else if (start == limit) {
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// Empty filters do not match any keys
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return false;
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}
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}
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return true; // Errors are treated as potential matches
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}
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}
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