You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
111 lines
3.3 KiB
111 lines
3.3 KiB
// 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 "leveldb/filter_policy.h"
|
|
#include "util/coding.h"
|
|
|
|
namespace leveldb {
|
|
|
|
// 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 FilterPolicy* policy)
|
|
: policy_(policy) {
|
|
}
|
|
|
|
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();
|
|
}
|
|
}
|
|
|
|
void FilterBlockBuilder::AddKey(const Slice& key) {
|
|
Slice k = key;
|
|
start_.push_back(keys_.size());
|
|
keys_.append(k.data(), k.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_keys = start_.size();
|
|
if (num_keys == 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(keys_.size()); // Simplify length computation
|
|
tmp_keys_.resize(num_keys);
|
|
for (size_t i = 0; i < num_keys; i++) {
|
|
const char* base = keys_.data() + start_[i];
|
|
size_t length = start_[i+1] - start_[i];
|
|
tmp_keys_[i] = Slice(base, length);
|
|
}
|
|
|
|
// Generate filter for current set of keys and append to result_.
|
|
filter_offsets_.push_back(result_.size());
|
|
policy_->CreateFilter(&tmp_keys_[0], num_keys, &result_);
|
|
|
|
tmp_keys_.clear();
|
|
keys_.clear();
|
|
start_.clear();
|
|
}
|
|
|
|
FilterBlockReader::FilterBlockReader(const FilterPolicy* policy,
|
|
const Slice& contents)
|
|
: policy_(policy),
|
|
data_(NULL),
|
|
offset_(NULL),
|
|
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;
|
|
}
|
|
|
|
bool FilterBlockReader::KeyMayMatch(uint64_t block_offset, const Slice& key) {
|
|
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 <= (offset_ - data_)) {
|
|
Slice filter = Slice(data_ + start, limit - start);
|
|
return policy_->KeyMayMatch(key, filter);
|
|
} else if (start == limit) {
|
|
// Empty filters do not match any keys
|
|
return false;
|
|
}
|
|
}
|
|
return true; // Errors are treated as potential matches
|
|
}
|
|
|
|
}
|