给出leveldb源码当中comparator.cc中的void FindShortestSeparator()的调用关系和调用次数

在leveldb源码中，void FindShortestSeparator()函数的调用关系如下：

1. 函数原型: void FindShortestSeparator(std::string* start, const Slice& limit, const Comparator* cmp)

2. 被调用于VersionSet::CompactRange()函数中的：

void VersionSet::CompactRange(int level, const Slice* begin, const Slice* end) {
  ...
  while (r->Valid() &&
         vset_->icmp_.Compare(r->key(), end) < 0) {
    ...
    if (ikey.size() < smallest.size()) {
      smallest.swap(ikey);
    }
    if (smallest.empty() ||
        vset_->icmp_.Compare(largest.Encode(), ikey.Encode()) < 0) {
      largest = ikey;
    }
    ...
  }
  ...
  // If we have a base level, we should compact "slow" level zero
  // files if there is lots of space in the level above.
  if (level == 0 && !smallest.empty()) {
    InternalKey start_key(*smallest, kMaxSequenceNumber, kValueTypeForSeek);
    InternalKey end_key(*largest, 0, static_cast<ValueType>(0));
    std::string compaction_filename = CompactionFileName(vset_->dbname_, compact_pointer_[level+1]);
    Edit edit;
    edit.SetCompaction(level, 0, MaxFileSizeForLevel(level),
                       compact_pointer_[level], compact_pointer_[level+1]);
    vset_->LogAndApply(&edit, &mutex_);
    Compaction* c = vset_->compact_pointer_[level+1] = new Compaction(
        vset_->options_, level+1, vset_);
    c->input_version_ = vset_->current_;
    c->input_version_->Ref();
    c->input_version_->GetOverlappingInputs(level, &start_key, &end_key, &c->inputs_);
    c->EditCompactionRange(&start_key, &end_key);
    c->SetupOtherInputs();
    DoCompactionWork(c);
    c->Cleanup();
    vset_->compact_pointer_[level+1] = nullptr;
    MaybeScheduleCompaction();
  }
  ...
}

3. 调用次数

根据代码分析，FindShortestSeparator()函数在LevelDB中被调用的次数与LevelDB中的压缩次数有关，而压缩次数与LevelDB的运行情况及配置有关，因此无法提供精确的调用次数。