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LevelDB-course-Lab
atdalīts no building_data_management_systems.Xuanzhou.2024Fall.DaSE/leveldb_base


								// 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.


								#ifndef STORAGE_LEVELDB_INCLUDE_DB_H_

								#define STORAGE_LEVELDB_INCLUDE_DB_H_


								#include <stdint.h>

								#include <stdio.h>

								#include "include/iterator.h"

								#include "include/options.h"


								namespace leveldb {


								struct Options;

								struct ReadOptions;

								struct WriteOptions;


								class Snapshot;

								class WriteBatch;


								// Some internal types.  Clients should ignore.

								class WriteBatchInternal;


								struct Range {

								  Slice start;

								  Slice limit;


								  Range(const Slice& s, const Slice& l) : start(s), limit(l) { }

								};


								// A DB is a persistent ordered map from keys to values.

								class DB {

								 public:

								  // Open the database with the specified "name".

								  // Stores a pointer to a heap-allocated database in *dbptr and returns

								  // OK on success.

								  // Stores NULL in *dbptr and returns a non-OK status on error.

								  // Caller should delete *dbptr when it is no longer needed.

								  static Status Open(const Options& options,

								                     const std::string& name,

								                     DB** dbptr);


								  DB() { }

								  virtual ~DB();


								  // Set the database entry for "key" to "value".  Returns OK on success,

								  // and a non-OK status on error.

								  // Note: consider setting options.sync = false.

								  virtual Status Put(const WriteOptions& options,

								                     const Slice& key,

								                     const Slice& value) = 0;


								  // Remove the database entry (if any) for "key".  Returns OK on

								  // success, and a non-OK status on error.  It is not an error if "key"

								  // did not exist in the database.

								  // Note: consider setting options.sync = false.

								  virtual Status Delete(const WriteOptions& options, const Slice& key) = 0;


								  // Apply the specified updates to the database.

								  // Returns OK on success, non-OK on failure.

								  // Note: consider setting options.sync = false.

								  virtual Status Write(const WriteOptions& options, WriteBatch* updates) = 0;


								  // If the database contains an entry for "key" store the

								  // corresponding value in *value and return OK.

								  //

								  // If there is no entry for "key" leave *value unchanged and return

								  // a status for which Status::IsNotFound() returns true.

								  //

								  // May return some other Status on an error.

								  virtual Status Get(const ReadOptions& options,

								                     const Slice& key, std::string* value) = 0;


								  // Return a heap-allocated iterator over the contents of the database.

								  // The result of NewIterator() is initially invalid (caller must

								  // call one of the Seek methods on the iterator before using it).

								  //

								  // Caller should delete the iterator when it is no longer needed.

								  // The returned iterator should be deleted before this db is deleted.

								  virtual Iterator* NewIterator(const ReadOptions& options) = 0;


								  // Return a handle to the current DB state.  Iterators created with

								  // this handle will all observe a stable snapshot of the current DB

								  // state.  The caller must call ReleaseSnapshot(result) when the

								  // snapshot is no longer needed.

								  virtual const Snapshot* GetSnapshot() = 0;


								  // Release a previously acquired snapshot.  The caller must not

								  // use "snapshot" after this call.

								  virtual void ReleaseSnapshot(const Snapshot* snapshot) = 0;


								  // DB implementations can export properties about their state

								  // via this method.  If "property" is a valid property understood by this

								  // DB implementation, fills "*value" with its current value and returns

								  // true.  Otherwise returns false.

								  //

								  //

								  // Valid property names include:

								  //

								  //  "leveldb.num-files-at-level<N>" - return the number of files at level <N>,

								  //     where <N> is an ASCII representation of a level number (e.g. "0").

								  virtual bool GetProperty(const Slice& property, uint64_t* value) = 0;


								  // For each i in [0,n-1], store in "sizes[i]", the approximate

								  // file system space used by keys in "[range[i].start .. range[i].limit)".

								  //

								  // Note that the returned sizes measure file system space usage, so

								  // if the user data compresses by a factor of ten, the returned

								  // sizes will be one-tenth the size of the corresponding user data size.

								  //

								  // The results may not include the sizes of recently written data.

								  virtual void GetApproximateSizes(const Range* range, int n,

								                                   uint64_t* sizes) = 0;


								  // Possible extensions:

								  // (1) Add a method to compact a range of keys


								 private:

								  // No copying allowed

								  DB(const DB&);

								  void operator=(const DB&);

								};


								// Destroy the contents of the specified database.

								// Be very careful using this method.

								Status DestroyDB(const std::string& name, const Options& options);


								// If a DB cannot be opened, you may attempt to call this method to

								// resurrect as much of the contents of the database as possible.

								// Some data may be lost, so be careful when calling this function

								// on a database that contains important information.

								Status RepairDB(const std::string& dbname, const Options& options);


								}


								#endif  // STORAGE_LEVELDB_INCLUDE_DB_H_