Summary:
1. Make filter_block.h a base class. Derive block_based_filter_block and full_filter_block. The previous one is the traditional filter block. The full_filter_block is newly added. It would generate a filter block that contain all the keys in SST file.
2. When querying a key, table would first check if full_filter is available. If not, it would go to the exact data block and check using block_based filter.
3. User could choose to use full_filter or tradional(block_based_filter). They would be stored in SST file with different meta index name. "filter.filter_policy" or "full_filter.filter_policy". Then, Table reader is able to know the fllter block type.
4. Some optimizations have been done for full_filter_block, thus it requires a different interface compared to the original one in filter_policy.h.
5. Actual implementation of filter bits coding/decoding is placed in util/bloom_impl.cc
Benchmark: base commit 1d23b5c470
Command:
db_bench --db=/dev/shm/rocksdb --num_levels=6 --key_size=20 --prefix_size=20 --keys_per_prefix=0 --value_size=100 --write_buffer_size=134217728 --max_write_buffer_number=2 --target_file_size_base=33554432 --max_bytes_for_level_base=1073741824 --verify_checksum=false --max_background_compactions=4 --use_plain_table=0 --memtablerep=prefix_hash --open_files=-1 --mmap_read=1 --mmap_write=0 --bloom_bits=10 --bloom_locality=1 --memtable_bloom_bits=500000 --compression_type=lz4 --num=393216000 --use_hash_search=1 --block_size=1024 --block_restart_interval=16 --use_existing_db=1 --threads=1 --benchmarks=readrandom —disable_auto_compactions=1
Read QPS increase for about 30% from 2230002 to 2991411.
Test Plan:
make all check
valgrind db_test
db_stress --use_block_based_filter = 0
./auto_sanity_test.sh
Reviewers: igor, yhchiang, ljin, sdong
Reviewed By: sdong
Subscribers: dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D20979
202 lines
6.5 KiB
C++
202 lines
6.5 KiB
C++
// Copyright (c) 2013, Facebook, Inc. All rights reserved.
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// This source code is licensed under the BSD-style license found in the
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// LICENSE file in the root directory of this source tree. An additional grant
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// of patent rights can be found in the PATENTS file in the same directory.
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//
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// 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/block_based_filter_block.h"
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#include "db/dbformat.h"
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#include "rocksdb/filter_policy.h"
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#include "util/coding.h"
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namespace rocksdb {
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namespace {
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bool SamePrefix(const SliceTransform* prefix_extractor,
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const Slice& key1, const Slice& key2) {
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if (!prefix_extractor->InDomain(key1) &&
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!prefix_extractor->InDomain(key2)) {
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return true;
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} else if (!prefix_extractor->InDomain(key1) ||
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!prefix_extractor->InDomain(key2)) {
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return false;
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} else {
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return (prefix_extractor->Transform(key1) ==
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prefix_extractor->Transform(key2));
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}
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}
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} // namespace
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// See doc/table_format.txt 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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BlockBasedFilterBlockBuilder::BlockBasedFilterBlockBuilder(
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const SliceTransform* prefix_extractor,
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const BlockBasedTableOptions& table_opt)
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: policy_(table_opt.filter_policy.get()),
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prefix_extractor_(prefix_extractor),
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whole_key_filtering_(table_opt.whole_key_filtering) {
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assert(policy_);
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}
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void BlockBasedFilterBlockBuilder::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 BlockBasedFilterBlockBuilder::Add(const Slice& key) {
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added_to_start_ = 0;
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if (whole_key_filtering_) {
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AddKey(key);
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added_to_start_ = 1;
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}
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if (prefix_extractor_ && prefix_extractor_->InDomain(key)) {
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AddPrefix(key);
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}
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}
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// Add key to filter if needed
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inline void BlockBasedFilterBlockBuilder::AddKey(const Slice& key) {
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start_.push_back(entries_.size());
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entries_.append(key.data(), key.size());
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}
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// Add prefix to filter if needed
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inline void BlockBasedFilterBlockBuilder::AddPrefix(const Slice& key) {
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// get slice for most recently added entry
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Slice prev;
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if (start_.size() > added_to_start_) {
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size_t prev_start = start_[start_.size() - 1 - added_to_start_];
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const char* base = entries_.data() + prev_start;
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size_t length = entries_.size() - prev_start;
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prev = Slice(base, length);
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}
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// this assumes prefix(prefix(key)) == prefix(key), as the last
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// entry in entries_ may be either a key or prefix, and we use
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// prefix(last entry) to get the prefix of the last key.
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if (prev.size() == 0 || !SamePrefix(prefix_extractor_, key, prev)) {
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Slice prefix = prefix_extractor_->Transform(key);
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start_.push_back(entries_.size());
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entries_.append(prefix.data(), prefix.size());
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}
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}
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Slice BlockBasedFilterBlockBuilder::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 BlockBasedFilterBlockBuilder::GenerateFilter() {
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const size_t num_entries = start_.size();
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if (num_entries == 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(entries_.size()); // Simplify length computation
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tmp_entries_.resize(num_entries);
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for (size_t i = 0; i < num_entries; i++) {
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const char* base = entries_.data() + start_[i];
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size_t length = start_[i + 1] - start_[i];
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tmp_entries_[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_entries_[0], num_entries, &result_);
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tmp_entries_.clear();
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entries_.clear();
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start_.clear();
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}
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BlockBasedFilterBlockReader::BlockBasedFilterBlockReader(
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const SliceTransform* prefix_extractor,
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const BlockBasedTableOptions& table_opt,
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const Slice& contents, bool delete_contents_after_use)
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: policy_(table_opt.filter_policy.get()),
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prefix_extractor_(prefix_extractor),
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whole_key_filtering_(table_opt.whole_key_filtering),
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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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assert(policy_);
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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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if (delete_contents_after_use) {
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filter_data.reset(contents.data());
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}
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}
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bool BlockBasedFilterBlockReader::KeyMayMatch(const Slice& key,
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uint64_t block_offset) {
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assert(block_offset != kNotValid);
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if (!whole_key_filtering_) {
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return true;
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}
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return MayMatch(key, block_offset);
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}
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bool BlockBasedFilterBlockReader::PrefixMayMatch(const Slice& prefix,
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uint64_t block_offset) {
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assert(block_offset != kNotValid);
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if (!prefix_extractor_) {
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return true;
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}
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return MayMatch(prefix, block_offset);
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}
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bool BlockBasedFilterBlockReader::MayMatch(const Slice& entry,
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uint64_t block_offset) {
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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 <= (uint32_t)(offset_ - data_)) {
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Slice filter = Slice(data_ + start, limit - start);
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return policy_->KeyMayMatch(entry, filter);
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} else if (start == limit) {
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// Empty filters do not match any entries
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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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size_t BlockBasedFilterBlockReader::ApproximateMemoryUsage() const {
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return num_ * 4 + 5 + (offset_ - data_);
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}
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}
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