RocksDB调整SSTable的大小

struct AdvancedColumnFamilyOptions {
  // Target file size for compaction.
  // target_file_size_base is per-file size for level-1.
  // Target file size for level L can be calculated by
  // target_file_size_base * (target_file_size_multiplier ^ (L-1))
  // For example, if target_file_size_base is 2MB and
  // target_file_size_multiplier is 10, then each file on level-1 will
  // be 2MB, and each file on level 2 will be 20MB,
  // and each file on level-3 will be 200MB.
  //
  // Default: 64MB.
  //
  // Dynamically changeable through SetOptions() API
  uint64_t target_file_size_base = 64 * 1048576;

  // Control maximum total data size for a level.
  // max_bytes_for_level_base is the max total for level-1.
  // Maximum number of bytes for level L can be calculated as
  // (max_bytes_for_level_base) * (max_bytes_for_level_multiplier ^ (L-1))
  // For example, if max_bytes_for_level_base is 200MB, and if
  // max_bytes_for_level_multiplier is 10, total data size for level-1
  // will be 200MB, total file size for level-2 will be 2GB,
  // and total file size for level-3 will be 20GB.
  //
  // Default: 256MB.
  //
  // Dynamically changeable through SetOptions() API
  uint64_t max_bytes_for_level_base = 256 * 1048576;
};

struct ColumnFamilyOptions : public AdvancedColumnFamilyOptions {
  ...
};

struct Options : public DBOptions, public ColumnFamilyOptions {
  ...
};