mergeplan

type MergePlan struct {
	Tasks []*MergeTask
}

type MergePlanOptions struct {
	// Max # segments per logarithmic tier, or max width of any
	// logarithmic “step”.  Smaller values mean more merging but fewer
	// segments.  Should be >= SegmentsPerMergeTask, else you'll have
	// too much merging.
	MaxSegmentsPerTier int

	// Max size of any segment produced after merging.  Actual
	// merging, however, may produce segment sizes different than the
	// planner’s predicted sizes.
	MaxSegmentSize int64

	// The growth factor for each tier in a staircase of idealized
	// segments computed by CalcBudget().
	TierGrowth float64

	// The number of segments in any resulting MergeTask.  e.g.,
	// len(result.Tasks[ * ].Segments) == SegmentsPerMergeTask.
	SegmentsPerMergeTask int

	// Small segments are rounded up to this size, i.e., treated as
	// equal (floor) size for consideration.  This is to prevent lots
	// of tiny segments from resulting in a long tail in the index.
	FloorSegmentSize int64

	// Controls how aggressively merges that reclaim more deletions
	// are favored.  Higher values will more aggressively target
	// merges that reclaim deletions, but be careful not to go so high
	// that way too much merging takes place; a value of 3.0 is
	// probably nearly too high.  A value of 0.0 means deletions don't
	// impact merge selection.
	ReclaimDeletesWeight float64

	// Optional, defaults to mergeplan.CalcBudget().
	CalcBudget func(totalSize int64, firstTierSize int64,
		o *MergePlanOptions) (budgetNumSegments int)

	// Optional, defaults to mergeplan.ScoreSegments().
	ScoreSegments func(segments []Segment, o *MergePlanOptions) float64

	// Optional.
	Logger func(string)
}

type MergeTask struct {
	Segments []Segment
}

type Segment interface {
	// Unique id of the segment -- used for sorting.
	Id() uint64

	// Full segment size (the size before any logical deletions).
	FullSize() int64

	// Size of the live data of the segment; i.e., FullSize() minus
	// any logical deletions.
	LiveSize() int64
}