code: func (tmp *TieredMergePolicy) SetMaxMergeAtOnceExplicit(v int) *TieredMergePolicy {
  	assert2(v >= 2, fmt.Sprintf("maxMergeAtonceExplicit must be > 1 (got %v)", v))
  	tmp.maxMergeAtOnceExplicit = v
  	return tmp
  }
docs: /*
  Maximum number of segments to be merged at a time, during forceMerge
  or forceMergeDeletes. Default is 30.
  */