code: func (tmp *TieredMergePolicy) SetMaxMergeAtOnce(v int) *TieredMergePolicy {
  	assert2(v >= 2, fmt.Sprintf("maxMergeAtonce must be > 1 (got %v)", v))
  	tmp.maxMergeAtOnce = v
  	return tmp
  }
docs: /*
  Maximum number of segments to be merged at a time during "normal"
  merging. For explicit merging (e.g., forceMerge or forceMergeDeletes
  was called), see SetMaxMergeAtonceExplicit(). Default is 10.
  */