rocksdb/table/table_reader.h

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// Copyright (c) 2013, Facebook, Inc. All rights reserved.
// This source code is licensed under the BSD-style license found in the
// LICENSE file in the root directory of this source tree. An additional grant
// of patent rights can be found in the PATENTS file in the same directory.
//
// Copyright (c) 2011 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.
#pragma once
#include <memory>
namespace rocksdb {
class Iterator;
struct ParsedInternalKey;
class Slice;
class Arena;
struct ReadOptions;
struct TableProperties;
class GetContext;
// A Table is a sorted map from strings to strings. Tables are
// immutable and persistent. A Table may be safely accessed from
// multiple threads without external synchronization.
class TableReader {
public:
virtual ~TableReader() {}
// Returns a new iterator over the table contents.
// The result of NewIterator() is initially invalid (caller must
// call one of the Seek methods on the iterator before using it).
// arena: If not null, the arena needs to be used to allocate the Iterator.
// When destroying the iterator, the caller will not call "delete"
// but Iterator::~Iterator() directly. The destructor needs to destroy
// all the states but those allocated in arena.
virtual Iterator* NewIterator(const ReadOptions&, Arena* arena = nullptr) = 0;
// Given a key, return an approximate byte offset in the file where
// the data for that key begins (or would begin if the key were
// present in the file). The returned value is in terms of file
// bytes, and so includes effects like compression of the underlying data.
// E.g., the approximate offset of the last key in the table will
// be close to the file length.
virtual uint64_t ApproximateOffsetOf(const Slice& key) = 0;
// Set up the table for Compaction. Might change some parameters with
// posix_fadvise
virtual void SetupForCompaction() = 0;
virtual std::shared_ptr<const TableProperties> GetTableProperties() const = 0;
// Prepare work that can be done before the real Get()
virtual void Prepare(const Slice& target) {}
// Report an approximation of how much memory has been used.
virtual size_t ApproximateMemoryUsage() const = 0;
// Calls get_context->SaveValue() repeatedly, starting with
// the entry found after a call to Seek(key), until it returns false.
// May not make such a call if filter policy says that key is not present.
//
// get_context->MarkKeyMayExist needs to be called when it is configured to be
// memory only and the key is not found in the block cache.
//
// readOptions is the options for the read
// key is the key to search for
virtual Status Get(const ReadOptions& readOptions, const Slice& key,
GetContext* get_context) = 0;
};
} // namespace rocksdb