include/rocksdb/utilities/leveldb_options.h
//  Copyright (c) 2011-present, 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 <stddef.h>

namespace rocksdb {

class Cache;
class Comparator;
class Env;
class FilterPolicy;
class Logger;
struct Options;
class Snapshot;

enum CompressionType : char;

// Options to control the behavior of a database (passed to
// DB::Open). A LevelDBOptions object can be initialized as though
// it were a LevelDB Options object, and then it can be converted into
// a RocksDB Options object.
struct LevelDBOptions {
  // -------------------
  // Parameters that affect behavior

  // Comparator used to define the order of keys in the table.
  // Default: a comparator that uses lexicographic byte-wise ordering
  //
  // REQUIRES: The client must ensure that the comparator supplied
  // here has the same name and orders keys *exactly* the same as the
  // comparator provided to previous open calls on the same DB.
  const Comparator* comparator;

  // If true, the database will be created if it is missing.
  // Default: false
  bool create_if_missing;

  // If true, an error is raised if the database already exists.
  // Default: false
  bool error_if_exists;

  // If true, the implementation will do aggressive checking of the
  // data it is processing and will stop early if it detects any
  // errors.  This may have unforeseen ramifications: for example, a
  // corruption of one DB entry may cause a large number of entries to
  // become unreadable or for the entire DB to become unopenable.
  // Default: false
  bool paranoid_checks;

  // Use the specified object to interact with the environment,
  // e.g. to read/write files, schedule background work, etc.
  // Default: Env::Default()
  Env* env;

  // Any internal progress/error information generated by the db will
  // be written to info_log if it is non-NULL, or to a file stored
  // in the same directory as the DB contents if info_log is NULL.
  // Default: NULL
  Logger* info_log;

  // -------------------
  // Parameters that affect performance

  // Amount of data to build up in memory (backed by an unsorted log
  // on disk) before converting to a sorted on-disk file.
  //
  // Larger values increase performance, especially during bulk loads.
  // Up to two write buffers may be held in memory at the same time,
  // so you may wish to adjust this parameter to control memory usage.
  // Also, a larger write buffer will result in a longer recovery time
  // the next time the database is opened.
  //
  // Default: 4MB
  size_t write_buffer_size;

  // Number of open files that can be used by the DB.  You may need to
  // increase this if your database has a large working set (budget
  // one open file per 2MB of working set).
  //
  // Default: 1000
  int max_open_files;

  // Control over blocks (user data is stored in a set of blocks, and
  // a block is the unit of reading from disk).

  // If non-NULL, use the specified cache for blocks.
  // If NULL, leveldb will automatically create and use an 8MB internal cache.
  // Default: NULL
  Cache* block_cache;

  // Approximate size of user data packed per block.  Note that the
  // block size specified here corresponds to uncompressed data.  The
  // actual size of the unit read from disk may be smaller if
  // compression is enabled.  This parameter can be changed dynamically.
  //
  // Default: 4K
  size_t block_size;

  // Number of keys between restart points for delta encoding of keys.
  // This parameter can be changed dynamically.  Most clients should
  // leave this parameter alone.
  //
  // Default: 16
  int block_restart_interval;

  // Compress blocks using the specified compression algorithm.  This
  // parameter can be changed dynamically.
  //
  // Default: kSnappyCompression, which gives lightweight but fast
  // compression.
  //
  // Typical speeds of kSnappyCompression on an Intel(R) Core(TM)2 2.4GHz:
  //    ~200-500MB/s compression
  //    ~400-800MB/s decompression
  // Note that these speeds are significantly faster than most
  // persistent storage speeds, and therefore it is typically never
  // worth switching to kNoCompression.  Even if the input data is
  // incompressible, the kSnappyCompression implementation will
  // efficiently detect that and will switch to uncompressed mode.
  CompressionType compression;

  // If non-NULL, use the specified filter policy to reduce disk reads.
  // Many applications will benefit from passing the result of
  // NewBloomFilterPolicy() here.
  //
  // Default: NULL
  const FilterPolicy* filter_policy;

  // Create a LevelDBOptions object with default values for all fields.
  LevelDBOptions();
};

// Converts a LevelDBOptions object into a RocksDB Options object.
Options ConvertOptions(const LevelDBOptions& leveldb_options);

}  // namespace rocksdb
