code: func (tmp *TieredMergePolicy) SetSegmentsPerTier(v float64) *TieredMergePolicy {
  	assert2(v >= 2, fmt.Sprintf("segmentsPerTier must be >= 2 (got %v)", v))
  	tmp.segsPerTier = v
  	return tmp
  }
docs: /*
  Sets the allowed number of segments per tier. Smaller values mean
  more merging but fewer segments.
  
  NOTE: this value should be >= the SetMaxMergeAtOnce otherwise you'll
  force too much merging to occur.
  */