kevo/pkg/compaction/tiered.go

package compaction

import (
	"bytes"
	"fmt"
	"path/filepath"
	"sort"
	"time"

	"git.canoozie.net/jer/go-storage/pkg/config"
	"git.canoozie.net/jer/go-storage/pkg/iterator"
	"git.canoozie.net/jer/go-storage/pkg/sstable"
)

// TieredCompactor implements a tiered compaction strategy
type TieredCompactor struct {
	*Compactor
	
	// Next file sequence number
	nextFileSeq uint64
}

// NewTieredCompactor creates a new tiered compaction manager
func NewTieredCompactor(cfg *config.Config, sstableDir string) *TieredCompactor {
	return &TieredCompactor{
		Compactor:   NewCompactor(cfg, sstableDir),
		nextFileSeq: 1,
	}
}

// SelectCompaction selects files for tiered compaction
func (tc *TieredCompactor) SelectCompaction() (*CompactionTask, error) {
	// Reload SSTable information
	if err := tc.LoadSSTables(); err != nil {
		return nil, fmt.Errorf("failed to load SSTables: %w", err)
	}
	
	// Determine the maximum level
	maxLevel := 0
	for level := range tc.levels {
		if level > maxLevel {
			maxLevel = level
		}
	}
	
	// Check L0 first (special case due to potential overlaps)
	if len(tc.levels[0]) >= tc.cfg.MaxMemTables {
		return tc.selectL0Compaction()
	}
	
	// Check size-based conditions for other levels
	for level := 0; level < maxLevel; level++ {
		// If this level is too large compared to the next level
		thisLevelSize := tc.GetLevelSize(level)
		nextLevelSize := tc.GetLevelSize(level + 1)
		
		// If level is empty, skip it
		if thisLevelSize == 0 {
			continue
		}
		
		// If next level is empty, promote a file
		if nextLevelSize == 0 && len(tc.levels[level]) > 0 {
			return tc.selectPromotionCompaction(level)
		}
		
		// Check size ratio
		sizeRatio := float64(thisLevelSize) / float64(nextLevelSize)
		if sizeRatio >= tc.cfg.CompactionRatio {
			return tc.selectOverlappingCompaction(level)
		}
	}
	
	// No compaction needed
	return nil, nil
}

// selectL0Compaction selects files from L0 for compaction
func (tc *TieredCompactor) selectL0Compaction() (*CompactionTask, error) {
	// Require at least some files in L0
	if len(tc.levels[0]) < 2 {
		return nil, nil
	}
	
	// Sort L0 files by sequence number to prioritize older files
	files := make([]*SSTableInfo, len(tc.levels[0]))
	copy(files, tc.levels[0])
	sort.Slice(files, func(i, j int) bool {
		return files[i].Sequence < files[j].Sequence
	})
	
	// Take up to maxCompactFiles from L0
	maxCompactFiles := tc.cfg.MaxMemTables
	if maxCompactFiles > len(files) {
		maxCompactFiles = len(files)
	}
	
	selectedFiles := files[:maxCompactFiles]
	
	// Determine the key range covered by selected files
	var minKey, maxKey []byte
	for _, file := range selectedFiles {
		if len(minKey) == 0 || bytes.Compare(file.FirstKey, minKey) < 0 {
			minKey = file.FirstKey
		}
		if len(maxKey) == 0 || bytes.Compare(file.LastKey, maxKey) > 0 {
			maxKey = file.LastKey
		}
	}
	
	// Find overlapping files in L1
	var l1Files []*SSTableInfo
	for _, file := range tc.levels[1] {
		// Create a temporary SSTableInfo with the key range
		rangeInfo := &SSTableInfo{
			FirstKey: minKey,
			LastKey:  maxKey,
		}
		
		if file.Overlaps(rangeInfo) {
			l1Files = append(l1Files, file)
		}
	}
	
	// Create the compaction task
	task := &CompactionTask{
		InputFiles: map[int][]*SSTableInfo{
			0: selectedFiles,
			1: l1Files,
		},
		TargetLevel:        1,
		OutputPathTemplate: filepath.Join(tc.sstableDir, "%d_%06d_%020d.sst"),
	}
	
	return task, nil
}

// selectPromotionCompaction selects a file to promote to the next level
func (tc *TieredCompactor) selectPromotionCompaction(level int) (*CompactionTask, error) {
	// Sort files by sequence number
	files := make([]*SSTableInfo, len(tc.levels[level]))
	copy(files, tc.levels[level])
	sort.Slice(files, func(i, j int) bool {
		return files[i].Sequence < files[j].Sequence
	})
	
	// Select the oldest file
	file := files[0]
	
	// Create task to promote this file to the next level
	// No need to merge with any other files since the next level is empty
	task := &CompactionTask{
		InputFiles: map[int][]*SSTableInfo{
			level: {file},
		},
		TargetLevel:        level + 1,
		OutputPathTemplate: filepath.Join(tc.sstableDir, "%d_%06d_%020d.sst"),
	}
	
	return task, nil
}

// selectOverlappingCompaction selects files for compaction based on key overlap
func (tc *TieredCompactor) selectOverlappingCompaction(level int) (*CompactionTask, error) {
	// Sort files by sequence number to start with oldest
	files := make([]*SSTableInfo, len(tc.levels[level]))
	copy(files, tc.levels[level])
	sort.Slice(files, func(i, j int) bool {
		return files[i].Sequence < files[j].Sequence
	})
	
	// Select an initial file from this level
	file := files[0]
	
	// Find all overlapping files in the next level
	var nextLevelFiles []*SSTableInfo
	for _, nextFile := range tc.levels[level+1] {
		if file.Overlaps(nextFile) {
			nextLevelFiles = append(nextLevelFiles, nextFile)
		}
	}
	
	// Create the compaction task
	task := &CompactionTask{
		InputFiles: map[int][]*SSTableInfo{
			level:     {file},
			level + 1: nextLevelFiles,
		},
		TargetLevel:        level + 1,
		OutputPathTemplate: filepath.Join(tc.sstableDir, "%d_%06d_%020d.sst"),
	}
	
	return task, nil
}

// Compact performs compaction of the selected files
func (tc *TieredCompactor) Compact(task *CompactionTask) error {
	if task == nil {
		return nil // Nothing to compact
	}
	
	// Perform the compaction
	_, err := tc.CompactFiles(task)
	if err != nil {
		return fmt.Errorf("compaction failed: %w", err)
	}
	
	// Gather all input file paths for cleanup
	var inputPaths []string
	for _, files := range task.InputFiles {
		for _, file := range files {
			inputPaths = append(inputPaths, file.Path)
		}
	}
	
	// Delete the original files that were compacted
	if err := tc.DeleteCompactedFiles(inputPaths); err != nil {
		return fmt.Errorf("failed to clean up compacted files: %w", err)
	}
	
	// Reload SSTables to refresh our file list
	if err := tc.LoadSSTables(); err != nil {
		return fmt.Errorf("failed to reload SSTables: %w", err)
	}
	
	return nil
}

// CompactRange performs compaction on a specific key range
func (tc *TieredCompactor) CompactRange(minKey, maxKey []byte) error {
	// Create a range info to check for overlaps
	rangeInfo := &SSTableInfo{
		FirstKey: minKey,
		LastKey:  maxKey,
	}
	
	// Find files overlapping with the given range in each level
	task := &CompactionTask{
		InputFiles:         make(map[int][]*SSTableInfo),
		TargetLevel:        0, // Will be updated
		OutputPathTemplate: filepath.Join(tc.sstableDir, "%d_%06d_%020d.sst"),
	}
	
	// Get the maximum level
	var maxLevel int
	for level := range tc.levels {
		if level > maxLevel {
			maxLevel = level
		}
	}
	
	// Find overlapping files in each level
	for level := 0; level <= maxLevel; level++ {
		var overlappingFiles []*SSTableInfo
		
		for _, file := range tc.levels[level] {
			if file.Overlaps(rangeInfo) {
				overlappingFiles = append(overlappingFiles, file)
			}
		}
		
		if len(overlappingFiles) > 0 {
			task.InputFiles[level] = overlappingFiles
		}
	}
	
	// If no files overlap with the range, no compaction needed
	totalInputFiles := 0
	for _, files := range task.InputFiles {
		totalInputFiles += len(files)
	}
	
	if totalInputFiles == 0 {
		return nil
	}
	
	// Set target level to the maximum level + 1
	task.TargetLevel = maxLevel + 1
	
	// Perform the compaction
	return tc.Compact(task)
}

// RunCompaction performs a full compaction cycle
func (tc *TieredCompactor) RunCompaction() error {
	// Select files for compaction
	task, err := tc.SelectCompaction()
	if err != nil {
		return fmt.Errorf("failed to select files for compaction: %w", err)
	}
	
	// If no compaction needed, return
	if task == nil {
		return nil
	}
	
	// Perform the compaction
	return tc.Compact(task)
}

// MergeCompact merges iterators from multiple SSTables and writes to new files
func (tc *TieredCompactor) MergeCompact(readers []*sstable.Reader, targetLevel int) ([]string, error) {
	// Create iterators for all input files
	var iterators []iterator.Iterator
	for _, reader := range readers {
		iterators = append(iterators, reader.NewIterator())
	}
	
	// Create a merged iterator
	mergedIter := iterator.NewHierarchicalIterator(iterators)
	
	// Create a new output file
	timestamp := time.Now().UnixNano()
	outputPath := filepath.Join(tc.sstableDir, 
	                           fmt.Sprintf("%d_%06d_%020d.sst", 
	                                      targetLevel, tc.nextFileSeq, timestamp))
	tc.nextFileSeq++
	
	writer, err := sstable.NewWriter(outputPath)
	if err != nil {
		return nil, fmt.Errorf("failed to create SSTable writer: %w", err)
	}
	
	// Write all entries from the merged iterator
	var lastKey []byte
	var entriesWritten int
	
	mergedIter.SeekToFirst()
	for mergedIter.Valid() {
		key := mergedIter.Key()
		value := mergedIter.Value()
		
		// Skip duplicates
		if lastKey != nil && bytes.Equal(key, lastKey) {
			mergedIter.Next()
			continue
		}
		
		// Skip tombstones (nil values) during compaction
		if value != nil {
			if err := writer.Add(key, value); err != nil {
				writer.Abort()
				return nil, fmt.Errorf("failed to add entry to SSTable: %w", err)
			}
			entriesWritten++
		}
		
		lastKey = append(lastKey[:0], key...)
		mergedIter.Next()
	}
	
	// Finish writing
	if entriesWritten > 0 {
		if err := writer.Finish(); err != nil {
			return nil, fmt.Errorf("failed to finish SSTable: %w", err)
		}
		return []string{outputPath}, nil
	}
	
	// No entries written, abort the file
	writer.Abort()
	return nil, nil
}