feat: add backoff mechanism to the retention process

docs/sources/shared/configuration.md

@@ -1900,6 +1900,19 @@ The `compactor` block configures the compactor component, which compacts index s
 # CLI flag: -compactor.retention-table-timeout
 [retention_table_timeout: <duration> | default = 0s]
 
+retention_backoff_config:
+  # Minimum delay when backing off.
+  # CLI flag: -compactor.retention-backoff-config.backoff-min-period
+  [min_period: <duration> | default = 100ms]
+
+  # Maximum delay when backing off.
+  # CLI flag: -compactor.retention-backoff-config.backoff-max-period
+  [max_period: <duration> | default = 10s]
+
+  # Number of times to backoff and retry before failing.
+  # CLI flag: -compactor.retention-backoff-config.backoff-retries
+  [max_retries: <int> | default = 10]
+
 # Store used for managing delete requests.
 # CLI flag: -compactor.delete-request-store
 [delete_request_store: <string> | default = ""]

pkg/compactor/compactor.go

@@ -12,13 +12,15 @@ import (
 	"time"
 
 	"github.com/go-kit/log/level"
-	"github.com/grafana/dskit/kv"
-	"github.com/grafana/dskit/ring"
-	"github.com/grafana/dskit/services"
 	"github.com/pkg/errors"
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/common/model"
 
+	"github.com/grafana/dskit/backoff"
+	"github.com/grafana/dskit/kv"
+	"github.com/grafana/dskit/ring"
+	"github.com/grafana/dskit/services"
+
 	"github.com/grafana/loki/v3/pkg/analytics"
 	"github.com/grafana/loki/v3/pkg/compactor/deletion"
 	"github.com/grafana/loki/v3/pkg/compactor/retention"
@@ -77,6 +79,7 @@ type Config struct {
 	RetentionDeleteDelay        time.Duration       `yaml:"retention_delete_delay"`
 	RetentionDeleteWorkCount    int                 `yaml:"retention_delete_worker_count"`
 	RetentionTableTimeout       time.Duration       `yaml:"retention_table_timeout"`
+	RetentionBackoffConfig      backoff.Config      `yaml:"retention_backoff_config"`
 	DeleteRequestStore          string              `yaml:"delete_request_store"`
 	DeleteRequestStoreKeyPrefix string              `yaml:"delete_request_store_key_prefix"`
 	DeleteBatchSize             int                 `yaml:"delete_batch_size"`
@@ -110,6 +113,7 @@ func (cfg *Config) RegisterFlags(f *flag.FlagSet) {
 	f.IntVar(&cfg.TablesToCompact, "compactor.tables-to-compact", 0, "Number of tables that compactor will try to compact. Newer tables are chosen when this is less than the number of tables available.")
 	f.IntVar(&cfg.SkipLatestNTables, "compactor.skip-latest-n-tables", 0, "Do not compact N latest tables. Together with -compactor.run-once and -compactor.tables-to-compact, this is useful when clearing compactor backlogs.")
 
+	cfg.RetentionBackoffConfig.RegisterFlagsWithPrefix("compactor.retention-backoff-config", f)
 	// Ring
 	skipFlags := []string{
 		"compactor.ring.num-tokens",
@@ -323,7 +327,7 @@ func (c *Compactor) init(objectStoreClients map[config.DayTime]client.ObjectClie
 			}
 			chunkClient := client.NewClient(objectClient, encoder, schemaConfig)
 
-			sc.sweeper, err = retention.NewSweeper(retentionWorkDir, chunkClient, c.cfg.RetentionDeleteWorkCount, c.cfg.RetentionDeleteDelay, r)
+			sc.sweeper, err = retention.NewSweeper(retentionWorkDir, chunkClient, c.cfg.RetentionDeleteWorkCount, c.cfg.RetentionDeleteDelay, c.cfg.RetentionBackoffConfig, r)
 			if err != nil {
 				return fmt.Errorf("failed to init sweeper: %w", err)
 			}

pkg/compactor/retention/retention.go

@@ -11,6 +11,7 @@ import (
 
 	"github.com/go-kit/log"
 	"github.com/go-kit/log/level"
+	"github.com/grafana/dskit/backoff"
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/common/model"
 	"github.com/prometheus/prometheus/model/labels"
@@ -272,9 +273,17 @@ type Sweeper struct {
 	markerProcessor MarkerProcessor
 	chunkClient     ChunkClient
 	sweeperMetrics  *sweeperMetrics
+	backoffConfig   backoff.Config
 }
 
-func NewSweeper(workingDir string, deleteClient ChunkClient, deleteWorkerCount int, minAgeDelete time.Duration, r prometheus.Registerer) (*Sweeper, error) {
+func NewSweeper(
+	workingDir string,
+	deleteClient ChunkClient,
+	deleteWorkerCount int,
+	minAgeDelete time.Duration,
+	backoffConfig backoff.Config,
+	r prometheus.Registerer,
+) (*Sweeper, error) {
 	m := newSweeperMetrics(r)
 
 	p, err := newMarkerStorageReader(workingDir, deleteWorkerCount, minAgeDelete, m)
@@ -285,34 +294,43 @@ func NewSweeper(workingDir string, deleteClient ChunkClient, deleteWorkerCount i
 		markerProcessor: p,
 		chunkClient:     deleteClient,
 		sweeperMetrics:  m,
+		backoffConfig:   backoffConfig,
 	}, nil
 }
 
 func (s *Sweeper) Start() {
-	s.markerProcessor.Start(func(ctx context.Context, chunkId []byte) error {
-		status := statusSuccess
-		start := time.Now()
-		defer func() {
-			s.sweeperMetrics.deleteChunkDurationSeconds.WithLabelValues(status).Observe(time.Since(start).Seconds())
-		}()
-		chunkIDString := unsafeGetString(chunkId)
-		userID, err := getUserIDFromChunkID(chunkId)
-		if err != nil {
-			return err
-		}
+	s.markerProcessor.Start(s.deleteChunk)
+}
 
+func (s *Sweeper) deleteChunk(ctx context.Context, chunkID []byte) error {
+	status := statusSuccess
+	start := time.Now()
+	defer func() {
+		s.sweeperMetrics.deleteChunkDurationSeconds.WithLabelValues(status).Observe(time.Since(start).Seconds())
+	}()
+	chunkIDString := unsafeGetString(chunkID)
+	userID, err := getUserIDFromChunkID(chunkID)
+	if err != nil {
+		return err
+	}
+
+	retry := backoff.New(ctx, s.backoffConfig)
+	for retry.Ongoing() {
 		err = s.chunkClient.DeleteChunk(ctx, unsafeGetString(userID), chunkIDString)
+		if err == nil {
+			return nil
+		}
 		if s.chunkClient.IsChunkNotFoundErr(err) {
 			status = statusNotFound
 			level.Debug(util_log.Logger).Log("msg", "delete on not found chunk", "chunkID", chunkIDString)
 			return nil
 		}
-		if err != nil {
-			level.Error(util_log.Logger).Log("msg", "error deleting chunk", "chunkID", chunkIDString, "err", err)
-			status = statusFailure
-		}
-		return err
-	})
+		retry.Wait()
+	}
+
+	level.Error(util_log.Logger).Log("msg", "error deleting chunk", "chunkID", chunkIDString, "err", err)
+	status = statusFailure
+	return err
 }
 
 func getUserIDFromChunkID(chunkID []byte) ([]byte, error) {

pkg/compactor/retention/retention_test.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"crypto/sha256"
 	"encoding/base64"
+	"fmt"
 	"os"
 	"path"
 	"path/filepath"
@@ -14,6 +15,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/grafana/dskit/backoff"
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/common/model"
 	"github.com/prometheus/prometheus/model/labels"
@@ -31,14 +33,37 @@ import (
 )
 
 type mockChunkClient struct {
-	mtx           sync.Mutex
-	deletedChunks map[string]struct{}
+	mtx              sync.Mutex
+	deletedChunks    map[string]struct{}
+	unstableDeletion bool
+	perObjectCounter map[string]uint32
+}
+
+// newMockChunkClient creates a client that fails every first call to DeleteChunk if `unstableDeletion` is true.
+func newMockChunkClient(unstableDeletion bool) *mockChunkClient {
+	return &mockChunkClient{
+		deletedChunks:    map[string]struct{}{},
+		unstableDeletion: unstableDeletion,
+		perObjectCounter: map[string]uint32{},
+	}
+}
+
+// shouldFail returns true for every first call
+func (m *mockChunkClient) shouldFail(objectKey string) bool {
+	if !m.unstableDeletion {
+		return false
+	}
+	shouldFail := m.perObjectCounter[objectKey]%2 == 0
+	m.perObjectCounter[objectKey]++
+	return shouldFail
 }
 
 func (m *mockChunkClient) DeleteChunk(_ context.Context, _, chunkID string) error {
 	m.mtx.Lock()
 	defer m.mtx.Unlock()
-
+	if m.shouldFail(chunkID) {
+		return fmt.Errorf("chunk deletion for chunkID:%s is failed by mockChunkClient", chunkID)
+	}
 	m.deletedChunks[string([]byte(chunkID))] = struct{}{} // forces a copy, because this string is only valid within the delete fn.
 	return nil
 }
@@ -143,8 +168,9 @@ func Test_Retention(t *testing.T) {
 			// marks and sweep
 			expiration := NewExpirationChecker(tt.limits)
 			workDir := filepath.Join(t.TempDir(), "retention")
-			chunkClient := &mockChunkClient{deletedChunks: map[string]struct{}{}}
-			sweep, err := NewSweeper(workDir, chunkClient, 10, 0, nil)
+			// must not fail the process because deletion must be retried
+			chunkClient := newMockChunkClient(true)
+			sweep, err := NewSweeper(workDir, chunkClient, 10, 0, backoff.Config{MaxRetries: 2}, nil)
 			require.NoError(t, err)
 			sweep.Start()
 			defer sweep.Stop()
@@ -175,6 +201,38 @@ func Test_Retention(t *testing.T) {
 	}
 }
 
+func Test_Sweeper_deleteChunk(t *testing.T) {
+	chunkID := "1/3fff2c2d7595e046:1916fa8c4bd:1916fdfb33d:bd55fc5"
+	tests := map[string]struct {
+		maxRetries    int
+		expectedError error
+	}{
+		"expected error if chunk is not deleted and retry is disabled": {
+			maxRetries:    1,
+			expectedError: fmt.Errorf("chunk deletion for chunkID:%s is failed by mockChunkClient", chunkID),
+		},
+		"expected  no error if chunk is not deleted at the first attempt but retried": {
+			maxRetries: 2,
+		},
+	}
+	for name, data := range tests {
+		t.Run(name, func(t *testing.T) {
+			workDir := filepath.Join(t.TempDir(), "retention")
+			chunkClient := newMockChunkClient(true)
+			sweep, err := NewSweeper(workDir, chunkClient, 10, 0, backoff.Config{MaxRetries: data.maxRetries}, nil)
+			require.NoError(t, err)
+
+			err = sweep.deleteChunk(context.Background(), []byte(chunkID))
+			if data.expectedError != nil {
+				require.Equal(t, data.expectedError, err)
+			} else {
+				require.NoError(t, err)
+			}
+		})
+	}
+
+}
+
 type noopWriter struct {
 	count int64
 }