feature: configurable janitor interval and deletion batch size (#715)

* feature: configurable janitor interval and deletion batch size

* warn user when they set a big number of janitor batch size

* Update CHANGELOG.md

---------

Co-authored-by: Agung Hariadi Tedja <agung.tedja@kumparan.com>

CHANGELOG.md

@@ -7,6 +7,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+## [0.25.0] - 2023-01-02
+
+### Added
+- Added configuration for Janitor's Interval and Deletion Batch Size (PR: https://github.com/hibiken/asynq/pull/715)
+
 ## [0.24.1] - 2023-05-01
 
 ### Changed

internal/base/base.go

@@ -737,7 +737,7 @@ type Broker interface {
 	ReclaimStaleAggregationSets(qname string) error
 
 	// Task retention related method
-	DeleteExpiredCompletedTasks(qname string) error
+	DeleteExpiredCompletedTasks(qname string, batchSize int) error
 
 	// Lease related methods
 	ListLeaseExpired(cutoff time.Time, qnames ...string) ([]*TaskMessage, error)

internal/rdb/rdb.go

@@ -1241,9 +1241,7 @@ return table.getn(ids)`)
 
 // DeleteExpiredCompletedTasks checks for any expired tasks in the given queue's completed set,
 // and delete all expired tasks.
-func (r *RDB) DeleteExpiredCompletedTasks(qname string) error {
-	// Note: Do this operation in fix batches to prevent long running script.
-	const batchSize = 100
+func (r *RDB) DeleteExpiredCompletedTasks(qname string, batchSize int) error {
 	for {
 		n, err := r.deleteExpiredCompletedTasks(qname, batchSize)
 		if err != nil {

internal/rdb/rdb_test.go

@@ -2542,8 +2542,8 @@ func TestDeleteExpiredCompletedTasks(t *testing.T) {
 		h.FlushDB(t, r.client)
 		h.SeedAllCompletedQueues(t, r.client, tc.completed)
 
-		if err := r.DeleteExpiredCompletedTasks(tc.qname); err != nil {
-			t.Errorf("DeleteExpiredCompletedTasks(%q) failed: %v", tc.qname, err)
+		if err := r.DeleteExpiredCompletedTasks(tc.qname, 100); err != nil {
+			t.Errorf("DeleteExpiredCompletedTasks(%q, 100) failed: %v", tc.qname, err)
 			continue
 		}
 

internal/testbroker/testbroker.go

@@ -11,8 +11,8 @@ import (
 	"sync"
 	"time"
 
-	"github.com/redis/go-redis/v9"
 	"github.com/hibiken/asynq/internal/base"
+	"github.com/redis/go-redis/v9"
 )
 
 var errRedisDown = errors.New("testutil: redis is down")
@@ -145,13 +145,13 @@ func (tb *TestBroker) ForwardIfReady(qnames ...string) error {
 	return tb.real.ForwardIfReady(qnames...)
 }
 
-func (tb *TestBroker) DeleteExpiredCompletedTasks(qname string) error {
+func (tb *TestBroker) DeleteExpiredCompletedTasks(qname string, batchSize int) error {
 	tb.mu.Lock()
 	defer tb.mu.Unlock()
 	if tb.sleeping {
 		return errRedisDown
 	}
-	return tb.real.DeleteExpiredCompletedTasks(qname)
+	return tb.real.DeleteExpiredCompletedTasks(qname, batchSize)
 }
 
 func (tb *TestBroker) ListLeaseExpired(cutoff time.Time, qnames ...string) ([]*base.TaskMessage, error) {

janitor.go

@@ -27,13 +27,17 @@ type janitor struct {
 
 	// average interval between checks.
 	avgInterval time.Duration
+
+	// number of tasks to be deleted when janitor runs to delete the expired completed tasks.
+	batchSize int
 }
 
 type janitorParams struct {
-	logger   *log.Logger
-	broker   base.Broker
-	queues   []string
-	interval time.Duration
+	logger    *log.Logger
+	broker    base.Broker
+	queues    []string
+	interval  time.Duration
+	batchSize int
 }
 
 func newJanitor(params janitorParams) *janitor {
@@ -43,6 +47,7 @@ func newJanitor(params janitorParams) *janitor {
 		done:        make(chan struct{}),
 		queues:      params.queues,
 		avgInterval: params.interval,
+		batchSize:   params.batchSize,
 	}
 }
 
@@ -73,7 +78,7 @@ func (j *janitor) start(wg *sync.WaitGroup) {
 
 func (j *janitor) exec() {
 	for _, qname := range j.queues {
-		if err := j.broker.DeleteExpiredCompletedTasks(qname); err != nil {
+		if err := j.broker.DeleteExpiredCompletedTasks(qname, j.batchSize); err != nil {
 			j.logger.Errorf("Failed to delete expired completed tasks from queue %q: %v",
 				qname, err)
 		}

janitor_test.go

@@ -26,11 +26,13 @@ func TestJanitor(t *testing.T) {
 	defer r.Close()
 	rdbClient := rdb.NewRDB(r)
 	const interval = 1 * time.Second
+	const batchSize = 100
 	janitor := newJanitor(janitorParams{
-		logger:   testLogger,
-		broker:   rdbClient,
-		queues:   []string{"default", "custom"},
-		interval: interval,
+		logger:    testLogger,
+		broker:    rdbClient,
+		queues:    []string{"default", "custom"},
+		interval:  interval,
+		batchSize: batchSize,
 	})
 
 	now := time.Now()

server.go

@@ -239,6 +239,17 @@ type Config struct {
 	//
 	// If unset or nil, the group aggregation feature will be disabled on the server.
 	GroupAggregator GroupAggregator
+
+	// JanitorInterval specifies the average interval of janitor checks for expired completed tasks.
+	//
+	// If unset or zero, default interval of 8 seconds is used.
+	JanitorInterval time.Duration
+
+	// JanitorBatchSize specifies the number of expired completed tasks to be deleted in one run.
+	//
+	// If unset or zero, default batch size of 100 is used.
+	// Make sure to not put a big number as the batch size to prevent a long-running script.
+	JanitorBatchSize int
 }
 
 // GroupAggregator aggregates a group of tasks into one before the tasks are passed to the Handler.
@@ -408,6 +419,10 @@ const (
 	defaultDelayedTaskCheckInterval = 5 * time.Second
 
 	defaultGroupGracePeriod = 1 * time.Minute
+
+	defaultJanitorInterval = 8 * time.Second
+
+	defaultJanitorBatchSize = 100
 )
 
 // NewServer returns a new Server given a redis connection option
@@ -547,11 +562,26 @@ func NewServer(r RedisConnOpt, cfg Config) *Server {
 		interval:        healthcheckInterval,
 		healthcheckFunc: cfg.HealthCheckFunc,
 	})
+
+	janitorInterval := cfg.JanitorInterval
+	if janitorInterval == 0 {
+		janitorInterval = defaultJanitorInterval
+	}
+
+	janitorBatchSize := cfg.JanitorBatchSize
+	if janitorBatchSize == 0 {
+		janitorBatchSize = defaultJanitorBatchSize
+	}
+	if janitorBatchSize > defaultJanitorBatchSize {
+		logger.Warnf("Janitor batch size of %d is greater than the recommended batch size of %d. "+
+			"This might cause a long-running script", janitorBatchSize, defaultJanitorBatchSize)
+	}
 	janitor := newJanitor(janitorParams{
-		logger:   logger,
-		broker:   rdb,
-		queues:   qnames,
-		interval: 8 * time.Second,
+		logger:    logger,
+		broker:    rdb,
+		queues:    qnames,
+		interval:  janitorInterval,
+		batchSize: janitorBatchSize,
 	})
 	aggregator := newAggregator(aggregatorParams{
 		logger:          logger,