BlocksToDelete function in DB options (#7638)

* Optional retention filter for DB

Signed-off-by: Ganesh Vernekar <cs15btech11018@iith.ac.in>

* Fix review comments

Signed-off-by: Ganesh Vernekar <cs15btech11018@iith.ac.in>

* Specify len for the map creation

Signed-off-by: Ganesh Vernekar <cs15btech11018@iith.ac.in>

tsdb/db.go

@@ -118,19 +118,27 @@ type Options struct {
 	// SeriesLifecycleCallback specifies a list of callbacks that will be called during a lifecycle of a series.
 	// It is always a no-op in Prometheus and mainly meant for external users who import TSDB.
 	SeriesLifecycleCallback SeriesLifecycleCallback
+
+	// BlocksToDelete is a function which returns the blocks which can be deleted.
+	// It is always the default time and size based retention in Prometheus and
+	// mainly meant for external users who import TSDB.
+	BlocksToDelete BlocksToDeleteFunc
 }
 
+type BlocksToDeleteFunc func(blocks []*Block) map[ulid.ULID]struct{}
+
 // DB handles reads and writes of time series falling into
 // a hashed partition of a seriedb.
 type DB struct {
 	dir   string
 	lockf fileutil.Releaser
 
-	logger    log.Logger
-	metrics   *dbMetrics
-	opts      *Options
-	chunkPool chunkenc.Pool
-	compactor Compactor
+	logger         log.Logger
+	metrics        *dbMetrics
+	opts           *Options
+	chunkPool      chunkenc.Pool
+	compactor      Compactor
+	blocksToDelete BlocksToDeleteFunc
 
 	// Mutex for that must be held when modifying the general block layout.
 	mtx    sync.RWMutex
@@ -560,14 +568,18 @@ func open(dir string, l log.Logger, r prometheus.Registerer, opts *Options, rngs
 	}
 
 	db = &DB{
-		dir:         dir,
-		logger:      l,
-		opts:        opts,
-		compactc:    make(chan struct{}, 1),
-		donec:       make(chan struct{}),
-		stopc:       make(chan struct{}),
-		autoCompact: true,
-		chunkPool:   chunkenc.NewPool(),
+		dir:            dir,
+		logger:         l,
+		opts:           opts,
+		compactc:       make(chan struct{}, 1),
+		donec:          make(chan struct{}),
+		stopc:          make(chan struct{}),
+		autoCompact:    true,
+		chunkPool:      chunkenc.NewPool(),
+		blocksToDelete: opts.BlocksToDelete,
+	}
+	if db.blocksToDelete == nil {
+		db.blocksToDelete = DefaultBlocksToDelete(db)
 	}
 
 	if !opts.NoLockfile {
@@ -871,13 +883,17 @@ func (db *DB) reload() (err error) {
 		return err
 	}
 
-	deletable := db.deletableBlocks(loadable)
+	deletableULIDs := db.blocksToDelete(loadable)
+	deletable := make(map[ulid.ULID]*Block, len(deletableULIDs))
 
 	// Corrupted blocks that have been superseded by a loadable block can be safely ignored.
 	// This makes it resilient against the process crashing towards the end of a compaction.
 	// Creation of a new block and deletion of its parents cannot happen atomically.
 	// By creating blocks with their parents, we can pick up the deletion where it left off during a crash.
 	for _, block := range loadable {
+		if _, ok := deletableULIDs[block.meta.ULID]; ok {
+			deletable[block.meta.ULID] = block
+		}
 		for _, b := range block.Meta().Compaction.Parents {
 			delete(corrupted, b.ULID)
 			deletable[b.ULID] = nil
@@ -986,9 +1002,17 @@ func openBlocks(l log.Logger, dir string, loaded []*Block, chunkPool chunkenc.Po
 	return blocks, corrupted, nil
 }
 
+// DefaultBlocksToDelete returns a filter which decides time based and size based
+// retention from the options of the db.
+func DefaultBlocksToDelete(db *DB) BlocksToDeleteFunc {
+	return func(blocks []*Block) map[ulid.ULID]struct{} {
+		return deletableBlocks(db, blocks)
+	}
+}
+
 // deletableBlocks returns all blocks past retention policy.
-func (db *DB) deletableBlocks(blocks []*Block) map[ulid.ULID]*Block {
-	deletable := make(map[ulid.ULID]*Block)
+func deletableBlocks(db *DB, blocks []*Block) map[ulid.ULID]struct{} {
+	deletable := make(map[ulid.ULID]struct{})
 
 	// Sort the blocks by time - newest to oldest (largest to smallest timestamp).
 	// This ensures that the retentions will remove the oldest  blocks.
@@ -998,34 +1022,36 @@ func (db *DB) deletableBlocks(blocks []*Block) map[ulid.ULID]*Block {
 
 	for _, block := range blocks {
 		if block.Meta().Compaction.Deletable {
-			deletable[block.Meta().ULID] = block
+			deletable[block.Meta().ULID] = struct{}{}
 		}
 	}
 
-	for ulid, block := range db.beyondTimeRetention(blocks) {
-		deletable[ulid] = block
+	for ulid := range BeyondTimeRetention(db, blocks) {
+		deletable[ulid] = struct{}{}
 	}
 
-	for ulid, block := range db.beyondSizeRetention(blocks) {
-		deletable[ulid] = block
+	for ulid := range BeyondSizeRetention(db, blocks) {
+		deletable[ulid] = struct{}{}
 	}
 
 	return deletable
 }
 
-func (db *DB) beyondTimeRetention(blocks []*Block) (deletable map[ulid.ULID]*Block) {
+// BeyondTimeRetention returns those blocks which are beyond the time retention
+// set in the db options.
+func BeyondTimeRetention(db *DB, blocks []*Block) (deletable map[ulid.ULID]struct{}) {
 	// Time retention is disabled or no blocks to work with.
 	if len(db.blocks) == 0 || db.opts.RetentionDuration == 0 {
 		return
 	}
 
-	deletable = make(map[ulid.ULID]*Block)
+	deletable = make(map[ulid.ULID]struct{})
 	for i, block := range blocks {
 		// The difference between the first block and this block is larger than
 		// the retention period so any blocks after that are added as deletable.
 		if i > 0 && blocks[0].Meta().MaxTime-block.Meta().MaxTime > db.opts.RetentionDuration {
 			for _, b := range blocks[i:] {
-				deletable[b.meta.ULID] = b
+				deletable[b.meta.ULID] = struct{}{}
 			}
 			db.metrics.timeRetentionCount.Inc()
 			break
@@ -1034,13 +1060,15 @@ func (db *DB) beyondTimeRetention(blocks []*Block) (deletable map[ulid.ULID]*Blo
 	return deletable
 }
 
-func (db *DB) beyondSizeRetention(blocks []*Block) (deletable map[ulid.ULID]*Block) {
+// BeyondSizeRetention returns those blocks which are beyond the size retention
+// set in the db options.
+func BeyondSizeRetention(db *DB, blocks []*Block) (deletable map[ulid.ULID]struct{}) {
 	// Size retention is disabled or no blocks to work with.
 	if len(db.blocks) == 0 || db.opts.MaxBytes <= 0 {
 		return
 	}
 
-	deletable = make(map[ulid.ULID]*Block)
+	deletable = make(map[ulid.ULID]struct{})
 
 	walSize, _ := db.Head().wal.Size()
 	headChunksSize := db.Head().chunkDiskMapper.Size()
@@ -1052,7 +1080,7 @@ func (db *DB) beyondSizeRetention(blocks []*Block) (deletable map[ulid.ULID]*Blo
 		if blocksSize > int64(db.opts.MaxBytes) {
 			// Add this and all following blocks for deletion.
 			for _, b := range blocks[i:] {
-				deletable[b.meta.ULID] = b
+				deletable[b.meta.ULID] = struct{}{}
 			}
 			db.metrics.sizeRetentionCount.Inc()
 			break