storage: suggest compaction when replicas are deleted

In aggregate, if enough contiguous replicas are migrated away from a
range, we would like to compact the underlying RocksDB storage engine.
To that end, on clear a replica's data, we suggest a compaction.

Release note: None

pkg/storage/client_raft_test.go

@@ -3858,3 +3858,53 @@ func TestFailedConfChange(t *testing.T) {
 		t.Fatal(err)
 	}
 }
+
+// TestStoreRangeRemovalCompactionSuggestion verifies that if a replica
+// is removed from a store, a compaction suggestion is made to the
+// compactor queue.
+func TestStoreRangeRemovalCompactionSuggestion(t *testing.T) {
+	defer leaktest.AfterTest(t)()
+	sc := storage.TestStoreConfig(nil)
+	mtc := &multiTestContext{storeConfig: &sc}
+	defer mtc.Stop()
+	mtc.Start(t, 3)
+
+	const rangeID = roachpb.RangeID(1)
+	mtc.replicateRange(rangeID, 1, 2)
+
+	repl, err := mtc.stores[0].GetReplica(rangeID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	ctx := repl.AnnotateCtx(context.Background())
+
+	deleteStore := mtc.stores[2]
+	if err := repl.ChangeReplicas(
+		ctx,
+		roachpb.REMOVE_REPLICA,
+		roachpb.ReplicationTarget{
+			NodeID:  deleteStore.Ident.NodeID,
+			StoreID: deleteStore.Ident.StoreID,
+		},
+		repl.Desc(),
+		storage.ReasonRebalance,
+		"",
+	); err != nil {
+		t.Fatal(err)
+	}
+
+	testutils.SucceedsSoon(t, func() error {
+		// Check for a compaction metric indicating non-zero bytes are queued.
+		if c := mtc.stores[2].Compactor().Metrics.BytesQueued.Value(); c == 0 {
+			return errors.Errorf("expected non-zero bytes queued in suggested compaction queue; got %d", c)
+		}
+		// Verify that no compaction metrics are showing non-zero bytes in the
+		// other stores.
+		for i := 0; i < 2; i++ {
+			if c := mtc.stores[i].Compactor().Metrics.BytesQueued.Value(); c != 0 {
+				return errors.Errorf("expected zero bytes queued in suggested compaction queue; got %d", c)
+			}
+		}
+		return nil
+	})
+}

pkg/storage/compactor/compactor.go

@@ -112,21 +112,25 @@ func NewCompactor(eng engine.WithSSTables, capFn storeCapacityFunc) *Compactor {
 // provided stopper indicates. Processing is done with a periodicity of
 // compactionMinInterval, but only if there are compactions pending.
 func (c *Compactor) Start(ctx context.Context, tracer opentracing.Tracer, stopper *stop.Stopper) {
-	if empty, err := c.isSpanEmpty(
-		ctx, keys.LocalStoreSuggestedCompactionsMin, keys.LocalStoreSuggestedCompactionsMax,
-	); err != nil {
-		log.Warningf(ctx, "failed check whether compaction suggestions exist: %s", err)
-	} else if !empty {
-		log.Eventf(ctx, "compactor starting in %s as there are suggested compactions pending", c.opts.CompactionMinInterval)
-		c.ch <- struct{}{} // wake up the goroutine immediately
-	}
+	// Wake up the goroutine immediately.
+	c.ch <- struct{}{}
 
 	stopper.RunWorker(ctx, func(ctx context.Context) {
 		var timer timeutil.Timer
 		var timerSet bool
 		for {
 			select {
 			case <-c.ch:
+				// A new suggestion was made. Examine the compaction queue,
+				// which updates the bytes queued stat in a timely fashion.
+				if bytesQueued, err := c.examineQueue(ctx); err != nil {
+					log.Warningf(ctx, "failed check whether compaction suggestions exist: %s", err)
+				} else if bytesQueued > 0 {
+					log.Eventf(ctx, "compactor starting in %s as there are suggested compactions pending", c.opts.CompactionMinInterval)
+				} else {
+					// Queue is empty, don't set the timer. This can happen only at startup.
+					break
+				}
 				// Set the wait timer if not already set.
 				if !timerSet {
 					timer.Reset(c.opts.CompactionMinInterval)
@@ -369,22 +373,26 @@ func (c *Compactor) aggregateCompaction(
 	return false // aggregated successfully
 }
 
-// isSpanEmpty returns whether the specified key span is empty (true)
-// or contains keys (false).
-func (c *Compactor) isSpanEmpty(ctx context.Context, start, end roachpb.Key) (bool, error) {
-	// If there are any suggested compactions, start the compaction timer.
-	var empty = true
+// examineQueue returns the total number of bytes queued and updates the
+// BytesQueued gauge.
+func (c *Compactor) examineQueue(ctx context.Context) (int64, error) {
+	var totalBytes int64
 	if err := c.eng.Iterate(
-		engine.MVCCKey{Key: start},
-		engine.MVCCKey{Key: end},
-		func(_ engine.MVCCKeyValue) (bool, error) {
-			empty = false
-			return true, nil // don't continue iteration
+		engine.MVCCKey{Key: keys.LocalStoreSuggestedCompactionsMin},
+		engine.MVCCKey{Key: keys.LocalStoreSuggestedCompactionsMax},
+		func(kv engine.MVCCKeyValue) (bool, error) {
+			var c storagebase.Compaction
+			if err := protoutil.Unmarshal(kv.Value, &c); err != nil {
+				return false, err
+			}
+			totalBytes += c.Bytes
+			return false, nil // continue iteration
 		},
 	); err != nil {
-		return false, err
+		return 0, err
 	}
-	return empty, nil
+	c.Metrics.BytesQueued.Update(totalBytes)
+	return totalBytes, nil
 }
 
 // SuggestCompaction writes the specified compaction to persistent

pkg/storage/compactor/compactor_test.go

@@ -567,10 +567,8 @@ func TestCompactorCleansUpOldRecords(t *testing.T) {
 			return fmt.Errorf("expected skipped bytes %d; got %d", e, a)
 		}
 		// Verify compaction queue is empty.
-		if empty, err := compactor.isSpanEmpty(
-			context.Background(), keys.LocalStoreSuggestedCompactionsMin, keys.LocalStoreSuggestedCompactionsMax,
-		); err != nil || !empty {
-			return fmt.Errorf("compaction queue not empty or err: %t, %v", empty, err)
+		if bytesQueued, err := compactor.examineQueue(context.Background()); err != nil || bytesQueued > 0 {
+			return fmt.Errorf("compaction queue not empty (%d bytes) or err %v", bytesQueued, err)
 		}
 		return nil
 	})

pkg/storage/replica.go

@@ -775,11 +775,22 @@ func (r *Replica) destroyDataRaftMuLocked(
 
 	// NB: this uses the local descriptor instead of the consistent one to match
 	// the data on disk.
-	if err := clearRangeData(ctx, r.Desc(), ms.KeyCount, r.store.Engine(), batch); err != nil {
+	desc := r.Desc()
+	if err := clearRangeData(ctx, desc, ms.KeyCount, r.store.Engine(), batch); err != nil {
 		return err
 	}
 	clearTime := timeutil.Now()
 
+	// Suggest the cleared range to the compactor queue.
+	r.store.compactor.SuggestCompaction(ctx, storagebase.SuggestedCompaction{
+		StartKey: roachpb.Key(desc.StartKey),
+		EndKey:   roachpb.Key(desc.EndKey),
+		Compaction: storagebase.Compaction{
+			Bytes:            ms.Total(),
+			SuggestedAtNanos: clearTime.UnixNano(),
+		},
+	})
+
 	// Save a tombstone to ensure that replica IDs never get reused.
 	if err := r.setTombstoneKey(ctx, batch, &consistentDesc); err != nil {
 		return err

pkg/storage/store.go

@@ -1771,6 +1771,9 @@ func (s *Store) DB() *client.DB { return s.cfg.DB }
 // Gossip accessor.
 func (s *Store) Gossip() *gossip.Gossip { return s.cfg.Gossip }
 
+// Compactor accessor.
+func (s *Store) Compactor() *compactor.Compactor { return s.compactor }
+
 // Stopper accessor.
 func (s *Store) Stopper() *stop.Stopper { return s.stopper }