filter_block_reader_common.h

//  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).
//

#pragma once

#include <cassert>
#include "table/block_based/cachable_entry.h"
#include "table/block_based/filter_block.h"

namespace rocksdb {

class BlockBasedTable;
class FilePrefetchBuffer;

// Encapsulates common functionality for the various filter block reader
// implementations. Provides access to the filter block regardless of whether
// it is owned by the reader or stored in the cache, or whether it is pinned
// in the cache or not.
template <typename TBlocklike>
class FilterBlockReaderCommon : public FilterBlockReader {
 public:
  FilterBlockReaderCommon(const BlockBasedTable* t,
                          CachableEntry<TBlocklike>&& filter_block)
      : table_(t), filter_block_(std::move(filter_block)) {
    assert(table_);
  }

 protected:
  static Status ReadFilterBlock(const BlockBasedTable* table,
                                FilePrefetchBuffer* prefetch_buffer,
                                const ReadOptions& read_options,
                                GetContext* get_context,
                                BlockCacheLookupContext* lookup_context,
                                CachableEntry<TBlocklike>* filter_block);

  const BlockBasedTable* table() const { return table_; }
  const SliceTransform* table_prefix_extractor() const;
  bool whole_key_filtering() const;

  Status GetOrReadFilterBlock(bool no_io, GetContext* get_context,
                              BlockCacheLookupContext* lookup_context,
                              CachableEntry<TBlocklike>* filter_block) const;

  size_t ApproximateFilterBlockMemoryUsage() const;

 private:
  const BlockBasedTable* table_;
  CachableEntry<TBlocklike> filter_block_;
};

}  // namespace rocksdb