text: //  Copyright (c) 2011-present, Facebook, Inc.  All rights reserved.
  //  This source code is licensed under both the GPLv2 (found in the
  //  COPYING file in the root directory) and Apache 2.0 License
  //  (found in the LICENSE.Apache file in the root 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/block_based/block_based_filter_block.h"
  #include <algorithm>
  
  #include "db/dbformat.h"
  #include "monitoring/perf_context_imp.h"
  #include "rocksdb/filter_policy.h"
  #include "table/block_based/block_based_table_reader.h"
  #include "test_util/testharness.h"
  #include "util/coding.h"
  #include "util/string_util.h"
  
  namespace ROCKSDB_NAMESPACE {
  
  namespace {
  
  void AppendItem(std::string* props, const std::string& key,
                  const std::string& value) {
    char cspace = ' ';
    std::string value_str("");
    size_t i = 0;
    const size_t dataLength = 64;
    const size_t tabLength = 2;
    const size_t offLength = 16;
  
    value_str.append(&value[i], std::min(size_t(dataLength), value.size()));
    i += dataLength;
    while (i < value.size()) {
      value_str.append("\n");
      value_str.append(offLength, cspace);
      value_str.append(&value[i], std::min(size_t(dataLength), value.size() - i));
      i += dataLength;
    }
  
    std::string result("");
    if (key.size() < (offLength - tabLength))
      result.append(size_t((offLength - tabLength)) - key.size(), cspace);
    result.append(key);
  
    props->append(result + ": " + value_str + "\n");
  }
  
  template <class TKey>
  void AppendItem(std::string* props, const TKey& key, const std::string& value) {
    std::string key_str = ROCKSDB_NAMESPACE::ToString(key);
    AppendItem(props, key_str, value);
  }
  }  // namespace
  
  // 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;
  
  BlockBasedFilterBlockBuilder::BlockBasedFilterBlockBuilder(
      const SliceTransform* prefix_extractor,
      const BlockBasedTableOptions& table_opt)
      : policy_(table_opt.filter_policy.get()),
        prefix_extractor_(prefix_extractor),
        whole_key_filtering_(table_opt.whole_key_filtering),
        prev_prefix_start_(0),
        prev_prefix_size_(0),
        num_added_(0) {
    assert(policy_);
  }
  
  void BlockBasedFilterBlockBuilder::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 BlockBasedFilterBlockBuilder::Add(const Slice& key) {
    if (prefix_extractor_ && prefix_extractor_->InDomain(key)) {
      AddPrefix(key);
    }
  
    if (whole_key_filtering_) {
      AddKey(key);
    }
  }
  
  // Add key to filter if needed
  inline void BlockBasedFilterBlockBuilder::AddKey(const Slice& key) {
    num_added_++;
    start_.push_back(entries_.size());
    entries_.append(key.data(), key.size());
  }
  
  // Add prefix to filter if needed
  inline void BlockBasedFilterBlockBuilder::AddPrefix(const Slice& key) {
    // get slice for most recently added entry
    Slice prev;
    if (prev_prefix_size_ > 0) {
      prev = Slice(entries_.data() + prev_prefix_start_, prev_prefix_size_);
    }
  
    Slice prefix = prefix_extractor_->Transform(key);
    // insert prefix only when it's different from the previous prefix.
    if (prev.size() == 0 || prefix != prev) {
      prev_prefix_start_ = entries_.size();
      prev_prefix_size_ = prefix.size();
      AddKey(prefix);
    }
  }
  
  Slice BlockBasedFilterBlockBuilder::Finish(const BlockHandle& /*tmp*/,
                                             Status* status) {
    // In this impl we ignore BlockHandle
    *status = Status::OK();
    if (!start_.empty()) {
      GenerateFilter();
    }
  
    // Append array of per-filter offsets
    const uint32_t array_offset = static_cast<uint32_t>(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 BlockBasedFilterBlockBuilder::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(static_cast<uint32_t>(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(static_cast<uint32_t>(result_.size()));
    policy_->CreateFilter(&tmp_entries_[0], static_cast<int>(num_entries),
                          &result_);
  
    tmp_entries_.clear();
    entries_.clear();
    start_.clear();
    prev_prefix_start_ = 0;
    prev_prefix_size_ = 0;
  }
  
  BlockBasedFilterBlockReader::BlockBasedFilterBlockReader(
      const BlockBasedTable* t, CachableEntry<BlockContents>&& filter_block)
      : FilterBlockReaderCommon(t, std::move(filter_block)) {
    assert(table());
    assert(table()->get_rep());
    assert(table()->get_rep()->filter_policy);
  }
  
  std::unique_ptr<FilterBlockReader> BlockBasedFilterBlockReader::Create(
      const BlockBasedTable* table, FilePrefetchBuffer* prefetch_buffer,
      bool use_cache, bool prefetch, bool pin,
      BlockCacheLookupContext* lookup_context) {
    assert(table);
    assert(table->get_rep());
    assert(!pin || prefetch);
  
    CachableEntry<BlockContents> filter_block;
    if (prefetch || !use_cache) {
      const Status s = ReadFilterBlock(table, prefetch_buffer, ReadOptions(),
                                       use_cache, nullptr /* get_context */,
                                       lookup_context, &filter_block);
      if (!s.ok()) {
        IGNORE_STATUS_IF_ERROR(s);
        return std::unique_ptr<FilterBlockReader>();
      }
  
      if (use_cache && !pin) {
        filter_block.Reset();
      }
    }
  
    return std::unique_ptr<FilterBlockReader>(
        new BlockBasedFilterBlockReader(table, std::move(filter_block)));
  }
  
  bool BlockBasedFilterBlockReader::KeyMayMatch(
      const Slice& key, const SliceTransform* /* prefix_extractor */,
      uint64_t block_offset, const bool no_io,
      const Slice* const /*const_ikey_ptr*/, GetContext* get_context,
      BlockCacheLookupContext* lookup_context) {
    assert(block_offset != kNotValid);
    if (!whole_key_filtering()) {
      return true;
    }
    return MayMatch(key, block_offset, no_io, get_context, lookup_context);
  }
  
  bool BlockBasedFilterBlockReader::PrefixMayMatch(
      const Slice& prefix, const SliceTransform* /* prefix_extractor */,
      uint64_t block_offset, const bool no_io,
      const Slice* const /*const_ikey_ptr*/, GetContext* get_context,
      BlockCacheLookupContext* lookup_context) {
    assert(block_offset != kNotValid);
    return MayMatch(prefix, block_offset, no_io, get_context, lookup_context);
  }
  
  bool BlockBasedFilterBlockReader::ParseFieldsFromBlock(
      const BlockContents& contents, const char** data, const char** offset,
      size_t* num, size_t* base_lg) {
    assert(data);
    assert(offset);
    assert(num);
    assert(base_lg);
  
    const size_t n = contents.data.size();
    if (n < 5) {  // 1 byte for base_lg and 4 for start of offset array
      return false;
    }
  
    const uint32_t last_word = DecodeFixed32(contents.data.data() + n - 5);
    if (last_word > n - 5) {
      return false;
    }
  
    *data = contents.data.data();
    *offset = (*data) + last_word;
    *num = (n - 5 - last_word) / 4;
    *base_lg = contents.data[n - 1];
  
    return true;
  }
  
  bool BlockBasedFilterBlockReader::MayMatch(
      const Slice& entry, uint64_t block_offset, bool no_io,
      GetContext* get_context, BlockCacheLookupContext* lookup_context) const {
    CachableEntry<BlockContents> filter_block;
  
    const Status s =
        GetOrReadFilterBlock(no_io, get_context, lookup_context, &filter_block);
    if (!s.ok()) {
      return true;
    }
  
    assert(filter_block.GetValue());
  
    const char* data = nullptr;
    const char* offset = nullptr;
    size_t num = 0;
    size_t base_lg = 0;
    if (!ParseFieldsFromBlock(*filter_block.GetValue(), &data, &offset, &num,
                              &base_lg)) {
      return true;  // Errors are treated as potential matches
    }
  
    const uint64_t index = block_offset >> base_lg;
    if (index < num) {
      const uint32_t start = DecodeFixed32(offset + index * 4);
      const uint32_t limit = DecodeFixed32(offset + index * 4 + 4);
      if (start <= limit && limit <= (uint32_t)(offset - data)) {
        const Slice filter = Slice(data + start, limit - start);
  
        assert(table());
        assert(table()->get_rep());
        const FilterPolicy* const policy = table()->get_rep()->filter_policy;
  
        const bool may_match = policy->KeyMayMatch(entry, filter);
        if (may_match) {
          PERF_COUNTER_ADD(bloom_sst_hit_count, 1);
          return true;
        } else {
          PERF_COUNTER_ADD(bloom_sst_miss_count, 1);
          return false;
        }
      } else if (start == limit) {
        // Empty filters do not match any entries
        return false;
      }
    }
    return true;  // Errors are treated as potential matches
  }
  
  size_t BlockBasedFilterBlockReader::ApproximateMemoryUsage() const {
    size_t usage = ApproximateFilterBlockMemoryUsage();
  #ifdef ROCKSDB_MALLOC_USABLE_SIZE
    usage += malloc_usable_size(const_cast<BlockBasedFilterBlockReader*>(this));
  #else
    usage += sizeof(*this);
  #endif  // ROCKSDB_MALLOC_USABLE_SIZE
    return usage;
  }
  
  std::string BlockBasedFilterBlockReader::ToString() const {
    CachableEntry<BlockContents> filter_block;
  
    const Status s =
        GetOrReadFilterBlock(false /* no_io */, nullptr /* get_context */,
                             nullptr /* lookup_context */, &filter_block);
    if (!s.ok()) {
      return std::string("Unable to retrieve filter block");
    }
  
    assert(filter_block.GetValue());
  
    const char* data = nullptr;
    const char* offset = nullptr;
    size_t num = 0;
    size_t base_lg = 0;
    if (!ParseFieldsFromBlock(*filter_block.GetValue(), &data, &offset, &num,
                              &base_lg)) {
      return std::string("Error parsing filter block");
    }
  
    std::string result;
    result.reserve(1024);
  
    std::string s_bo("Block offset"), s_hd("Hex dump"), s_fb("# filter blocks");
    AppendItem(&result, s_fb, ROCKSDB_NAMESPACE::ToString(num));
    AppendItem(&result, s_bo, s_hd);
  
    for (size_t index = 0; index < num; index++) {
      uint32_t start = DecodeFixed32(offset + index * 4);
      uint32_t limit = DecodeFixed32(offset + index * 4 + 4);
  
      if (start != limit) {
        result.append(" filter block # " +
                      ROCKSDB_NAMESPACE::ToString(index + 1) + "\n");
        Slice filter = Slice(data + start, limit - start);
        AppendItem(&result, start, filter.ToString(true));
      }
    }
    return result;
  }
  
  }  // namespace ROCKSDB_NAMESPACE
  