ceph/src/rocksdb/include/rocksdb/utilities/leveldb_options.h

   1 //  Copyright (c) 2011-present, Facebook, Inc.  All rights reserved.
   2 //  This source code is licensed under the BSD-style license found in the
   3 //  LICENSE file in the root directory of this source tree. An additional grant
   4 //  of patent rights can be found in the PATENTS file in the same directory.
   5 //
   6 // Copyright (c) 2011 The LevelDB Authors. All rights reserved.
   7 // Use of this source code is governed by a BSD-style license that can be
   8 // found in the LICENSE file. See the AUTHORS file for names of contributors.
   9
  10 #pragma once
  11
  12 #include <stddef.h>
  13
  14 namespace rocksdb {
  15
  16 class Cache;
  17 class Comparator;
  18 class Env;
  19 class FilterPolicy;
  20 class Logger;
  21 struct Options;
  22 class Snapshot;
  23
  24 enum CompressionType : unsigned char;
  25
  26 // Options to control the behavior of a database (passed to
  27 // DB::Open). A LevelDBOptions object can be initialized as though
  28 // it were a LevelDB Options object, and then it can be converted into
  29 // a RocksDB Options object.
  30 struct LevelDBOptions {
  31   // -------------------
  32   // Parameters that affect behavior
  33
  34   // Comparator used to define the order of keys in the table.
  35   // Default: a comparator that uses lexicographic byte-wise ordering
  36   //
  37   // REQUIRES: The client must ensure that the comparator supplied
  38   // here has the same name and orders keys *exactly* the same as the
  39   // comparator provided to previous open calls on the same DB.
  40   const Comparator* comparator;
  41
  42   // If true, the database will be created if it is missing.
  43   // Default: false
  44   bool create_if_missing;
  45
  46   // If true, an error is raised if the database already exists.
  47   // Default: false
  48   bool error_if_exists;
  49
  50   // If true, the implementation will do aggressive checking of the
  51   // data it is processing and will stop early if it detects any
  52   // errors.  This may have unforeseen ramifications: for example, a
  53   // corruption of one DB entry may cause a large number of entries to
  54   // become unreadable or for the entire DB to become unopenable.
  55   // Default: false
  56   bool paranoid_checks;
  57
  58   // Use the specified object to interact with the environment,
  59   // e.g. to read/write files, schedule background work, etc.
  60   // Default: Env::Default()
  61   Env* env;
  62
  63   // Any internal progress/error information generated by the db will
  64   // be written to info_log if it is non-NULL, or to a file stored
  65   // in the same directory as the DB contents if info_log is NULL.
  66   // Default: NULL
  67   Logger* info_log;
  68
  69   // -------------------
  70   // Parameters that affect performance
  71
  72   // Amount of data to build up in memory (backed by an unsorted log
  73   // on disk) before converting to a sorted on-disk file.
  74   //
  75   // Larger values increase performance, especially during bulk loads.
  76   // Up to two write buffers may be held in memory at the same time,
  77   // so you may wish to adjust this parameter to control memory usage.
  78   // Also, a larger write buffer will result in a longer recovery time
  79   // the next time the database is opened.
  80   //
  81   // Default: 4MB
  82   size_t write_buffer_size;
  83
  84   // Number of open files that can be used by the DB.  You may need to
  85   // increase this if your database has a large working set (budget
  86   // one open file per 2MB of working set).
  87   //
  88   // Default: 1000
  89   int max_open_files;
  90
  91   // Control over blocks (user data is stored in a set of blocks, and
  92   // a block is the unit of reading from disk).
  93
  94   // If non-NULL, use the specified cache for blocks.
  95   // If NULL, leveldb will automatically create and use an 8MB internal cache.
  96   // Default: NULL
  97   Cache* block_cache;
  98
  99   // Approximate size of user data packed per block.  Note that the
 100   // block size specified here corresponds to uncompressed data.  The
 101   // actual size of the unit read from disk may be smaller if
 102   // compression is enabled.  This parameter can be changed dynamically.
 103   //
 104   // Default: 4K
 105   size_t block_size;
 106
 107   // Number of keys between restart points for delta encoding of keys.
 108   // This parameter can be changed dynamically.  Most clients should
 109   // leave this parameter alone.
 110   //
 111   // Default: 16
 112   int block_restart_interval;
 113
 114   // Compress blocks using the specified compression algorithm.  This
 115   // parameter can be changed dynamically.
 116   //
 117   // Default: kSnappyCompression, which gives lightweight but fast
 118   // compression.
 119   //
 120   // Typical speeds of kSnappyCompression on an Intel(R) Core(TM)2 2.4GHz:
 121   //    ~200-500MB/s compression
 122   //    ~400-800MB/s decompression
 123   // Note that these speeds are significantly faster than most
 124   // persistent storage speeds, and therefore it is typically never
 125   // worth switching to kNoCompression.  Even if the input data is
 126   // incompressible, the kSnappyCompression implementation will
 127   // efficiently detect that and will switch to uncompressed mode.
 128   CompressionType compression;
 129
 130   // If non-NULL, use the specified filter policy to reduce disk reads.
 131   // Many applications will benefit from passing the result of
 132   // NewBloomFilterPolicy() here.
 133   //
 134   // Default: NULL
 135   const FilterPolicy* filter_policy;
 136
 137   // Create a LevelDBOptions object with default values for all fields.
 138   LevelDBOptions();
 139 };
 140
 141 // Converts a LevelDBOptions object into a RocksDB Options object.
 142 Options ConvertOptions(const LevelDBOptions& leveldb_options);
 143
 144 }  // namespace rocksdb