message: docs: add notes
diff: @@ -198,6 +198,9 @@ typedef unsigned(*HashFunction)(const char*);
  //type for the triple num
  //NOTICE: this should use unsigned (triple num may > 2500000000)
  typedef unsigned TYPE_TRIPLE_NUM;
  +//NOTICE: we do not use long long because it will consume more spaces in pre2num of Database
  +//For single machines, we aim to support 4.2B triples, and that's enough
  +//typedef long long TYPE_TRIPLE_NUM;
  //TODO: use long if need to run 5B dataset
  //type for entity/literal ID
  @@ -251,6 +254,7 @@ public:
  static const unsigned GB = 1073741824;
  //static const int TRIPLE_NUM_MAX = 1000*1000*1000;
  static const TYPE_TRIPLE_NUM TRIPLE_NUM_MAX = INVALID;
  + //static const TYPE_TRIPLE_NUM TRIPLE_NUM_MAX = (long long)10000*1000*1000;
  static const char EDGE_IN = 'i';
  static const char EDGE_OUT= 'o';
  