Allow switching from limits-based to interest-based retention in stream update

server/jetstream_cluster.go

@@ -6980,7 +6980,7 @@ func (s *Server) jsClusteredConsumerRequest(ci *ClientInfo, acc *Account, subjec
 	} else {
 		nca := ca.copyGroup()
 
-		rBefore := ca.Config.replicas(sa.Config)
+		rBefore := nca.Config.replicas(sa.Config)
 		rAfter := cfg.replicas(sa.Config)
 
 		var curLeader string

server/jetstream_test.go

@@ -21407,3 +21407,113 @@ func TestJetStreamServerReencryption(t *testing.T) {
 		})
 	}
 }
+
+func TestJetStreamLimitsToInterestPolicy(t *testing.T) {
+	c := createJetStreamClusterExplicit(t, "JSC", 3)
+	defer c.shutdown()
+
+	nc, js := jsClientConnect(t, c.leader())
+	defer nc.Close()
+
+	// This is the index of the consumer that we'll create as R1
+	// instead of R3, just to prove that it blocks the stream
+	// update from happening properly.
+	singleReplica := 3
+
+	streamCfg := nats.StreamConfig{
+		Name:      "TEST",
+		Subjects:  []string{"foo"},
+		Retention: nats.LimitsPolicy,
+		Storage:   nats.MemoryStorage,
+		Replicas:  3,
+	}
+
+	stream, err := js.AddStream(&streamCfg)
+	require_NoError(t, err)
+
+	for i := 0; i < 10; i++ {
+		replicas := streamCfg.Replicas
+		if i == singleReplica {
+			// Make one of the consumers R1 so that we can check
+			// that the switch to interest-based retention is also
+			// turning it into an R3 consumer.
+			replicas = 1
+		}
+		cname := fmt.Sprintf("test_%d", i)
+		_, err := js.AddConsumer("TEST", &nats.ConsumerConfig{
+			Name:      cname,
+			Durable:   cname,
+			AckPolicy: nats.AckAllPolicy,
+			Replicas:  replicas,
+		})
+		require_NoError(t, err)
+	}
+
+	for i := 0; i < 20; i++ {
+		_, err := js.Publish("foo", []byte{1, 2, 3, 4, 5})
+		require_NoError(t, err)
+	}
+
+	// Pull 10 or more messages from the stream. We will never pull
+	// less than 10, which guarantees that the lowest ack floor of
+	// all consumers should be 10.
+	for i := 0; i < 10; i++ {
+		cname := fmt.Sprintf("test_%d", i)
+		count := 10 + i // At least 10 messages
+
+		sub, err := js.PullSubscribe("foo", cname)
+		require_NoError(t, err)
+
+		msgs, err := sub.Fetch(count)
+		require_NoError(t, err)
+		require_Equal(t, len(msgs), count)
+		require_NoError(t, msgs[len(msgs)-1].AckSync())
+
+		// At this point the ack floor should match the count of
+		// messages we received.
+		info, err := js.ConsumerInfo("TEST", cname)
+		require_NoError(t, err)
+		require_Equal(t, info.AckFloor.Consumer, uint64(count))
+	}
+
+	// Try updating to interest-based. This should fail because
+	// we have a consumer that is R1 on an R3 stream.
+	streamCfg = stream.Config
+	streamCfg.Retention = nats.InterestPolicy
+	_, err = js.UpdateStream(&streamCfg)
+	require_Error(t, err)
+
+	// Now we'll make the R1 consumer an R3.
+	cname := fmt.Sprintf("test_%d", singleReplica)
+	cinfo, err := js.ConsumerInfo("TEST", cname)
+	require_NoError(t, err)
+
+	cinfo.Config.Replicas = streamCfg.Replicas
+	_, _ = js.UpdateConsumer("TEST", &cinfo.Config)
+	// TODO(nat): The jsConsumerCreateRequest update doesn't always
+	// respond when there are no errors updating a consumer, so this
+	// nearly always returns a timeout, despite actually doing what
+	// it should. We'll make sure the replicas were updated by doing
+	// another consumer info just to be sure.
+	// require_NoError(t, err)
+	c.waitOnAllCurrent()
+	cinfo, err = js.ConsumerInfo("TEST", cname)
+	require_NoError(t, err)
+	require_Equal(t, cinfo.Config.Replicas, streamCfg.Replicas)
+	require_Equal(t, len(cinfo.Cluster.Replicas), streamCfg.Replicas-1)
+
+	// This time it should succeed.
+	_, err = js.UpdateStream(&streamCfg)
+	require_NoError(t, err)
+
+	// We need to wait for all nodes to have applied the new stream
+	// configuration.
+	c.waitOnAllCurrent()
+
+	// Now we should only have 10 messages left in the stream, as
+	// each consumer has acked at least the first 10 messages.
+	info, err := js.StreamInfo("TEST")
+	require_NoError(t, err)
+	require_Equal(t, info.State.FirstSeq, 11)
+	require_Equal(t, info.State.Msgs, 10)
+}

server/stream.go

@@ -1495,9 +1495,11 @@ func (jsa *jsAccount) configUpdateCheck(old, new *StreamConfig, s *Server) (*Str
 	if cfg.Storage != old.Storage {
 		return nil, NewJSStreamInvalidConfigError(fmt.Errorf("stream configuration update can not change storage type"))
 	}
-	// Can't change retention.
+	// Can only change retention from limits to interest or back, not to/from work queue for now.
 	if cfg.Retention != old.Retention {
-		return nil, NewJSStreamInvalidConfigError(fmt.Errorf("stream configuration update can not change retention policy"))
+		if old.Retention == WorkQueuePolicy || cfg.Retention == WorkQueuePolicy {
+			return nil, NewJSStreamInvalidConfigError(fmt.Errorf("stream configuration update can not change retention policy to/from workqueue"))
+		}
 	}
 	// Can not have a template owner for now.
 	if old.Template != _EMPTY_ {
@@ -1785,9 +1787,41 @@ func (mset *stream) updateWithAdvisory(config *StreamConfig, sendAdvisory bool)
 		// a subsequent update to an existing tier will then move from existing past tier to existing new tier
 	}
 
+	if mset.isLeader() && ocfg.Retention != cfg.Retention && cfg.Retention == InterestPolicy {
+		// Before we can update the retention policy for the consumer, we need
+		// the replica count of all consumers to match the stream.
+		for _, c := range mset.sa.consumers {
+			if c.Config.Replicas > 0 && c.Config.Replicas != cfg.Replicas {
+				mset.mu.Unlock()
+				return fmt.Errorf("consumer %q replica count must be %d", c.Name, cfg.Replicas)
+			}
+		}
+	}
+
 	// Now update config and store's version of our config.
 	mset.cfg = *cfg
 
+	// If we're changing retention and haven't errored because of consumer
+	// replicas by now, whip through and update the consumer retention.
+	if ocfg.Retention != cfg.Retention && cfg.Retention == InterestPolicy {
+		toUpdate := make([]*consumer, 0, len(mset.consumers))
+		for _, c := range mset.consumers {
+			toUpdate = append(toUpdate, c)
+		}
+		mset.mu.Unlock()
+		for _, c := range toUpdate {
+			c.mu.Lock()
+			c.retention = cfg.Retention
+			c.mu.Unlock()
+			if c.retention == InterestPolicy {
+				// If we're switching to interest, force a check of the
+				// interest of existing stream messages.
+				c.checkStateForInterestStream()
+			}
+		}
+		mset.mu.Lock()
+	}
+
 	// If we are the leader never suppress update advisory, simply send.
 	if mset.isLeader() && sendAdvisory {
 		mset.sendUpdateAdvisoryLocked()

server/test_test.go

@@ -14,7 +14,6 @@
 package server
 
 import (
-	"bytes"
 	"fmt"
 	"math/rand"
 	"net/url"
@@ -112,17 +111,17 @@ func require_Error(t *testing.T, err error, expected ...error) {
 	t.Fatalf("Expected one of %v, got '%v'", expected, err)
 }
 
-func require_Equal(t *testing.T, a, b string) {
+func require_Equal[T comparable](t *testing.T, a, b T) {
 	t.Helper()
-	if strings.Compare(a, b) != 0 {
-		t.Fatalf("require equal, but got: %v != %v", a, b)
+	if a != b {
+		t.Fatalf("require %T equal, but got: %v != %v", a, a, b)
 	}
 }
 
-func require_NotEqual(t *testing.T, a, b [32]byte) {
+func require_NotEqual[T comparable](t *testing.T, a, b T) {
 	t.Helper()
-	if bytes.Equal(a[:], b[:]) {
-		t.Fatalf("require not equal, but got: %v != %v", a, b)
+	if a == b {
+		t.Fatalf("require %T not equal, but got: %v != %v", a, a, b)
 	}
 }