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nsqd: allow unbuffered memory chan if ephemeral or deferred #1376

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merged 1 commit into from
Aug 2, 2022
+22 −19
Merged

nsqd: allow unbuffered memory chan if ephemeral or deferred #1376

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8 changes: 4 additions & 4 deletions nsqd/channel.go
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Original file line number Diff line number Diff line change
Expand Up @@ -82,9 +82,10 @@ func NewChannel(topicName string, channelName string, nsqd *NSQD,
clients: make(map[int64]Consumer),
deleteCallback: deleteCallback,
nsqd: nsqd,
ephemeral: strings.HasSuffix(channelName, "#ephemeral"),
}
// create mem-queue only if size > 0 (do not use unbuffered chan)
if nsqd.getOpts().MemQueueSize > 0 {
// avoid mem-queue if size == 0 for more consistent ordering
if nsqd.getOpts().MemQueueSize > 0 || c.ephemeral {
c.memoryMsgChan = make(chan *Message, nsqd.getOpts().MemQueueSize)
}
if len(nsqd.getOpts().E2EProcessingLatencyPercentiles) > 0 {
Expand All @@ -96,8 +97,7 @@ func NewChannel(topicName string, channelName string, nsqd *NSQD,

c.initPQ()

if strings.HasSuffix(channelName, "#ephemeral") {
c.ephemeral = true
if c.ephemeral {
c.backend = newDummyBackendQueue()
} else {
dqLogf := func(level diskqueue.LogLevel, f string, args ...interface{}) {
Expand Down
33 changes: 18 additions & 15 deletions nsqd/topic.go
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Original file line number Diff line number Diff line change
Expand Up @@ -46,7 +46,7 @@ func NewTopic(topicName string, nsqd *NSQD, deleteCallback func(*Topic)) *Topic
t := &Topic{
name: topicName,
channelMap: make(map[string]*Channel),
memoryMsgChan: nil,
memoryMsgChan: make(chan *Message, nsqd.getOpts().MemQueueSize),
startChan: make(chan int, 1),
exitChan: make(chan int),
channelUpdateChan: make(chan int),
Expand All @@ -56,10 +56,6 @@ func NewTopic(topicName string, nsqd *NSQD, deleteCallback func(*Topic)) *Topic
deleteCallback: deleteCallback,
idFactory: NewGUIDFactory(nsqd.getOpts().ID),
}
// create mem-queue only if size > 0 (do not use unbuffered chan)
if nsqd.getOpts().MemQueueSize > 0 {
t.memoryMsgChan = make(chan *Message, nsqd.getOpts().MemQueueSize)
}
if strings.HasSuffix(topicName, "#ephemeral") {
t.ephemeral = true
t.backend = newDummyBackendQueue()
Expand Down Expand Up @@ -222,18 +218,25 @@ func (t *Topic) PutMessages(msgs []*Message) error {
}

func (t *Topic) put(m *Message) error {
select {
case t.memoryMsgChan <- m:
default:
err := writeMessageToBackend(m, t.backend)
t.nsqd.SetHealth(err)
if err != nil {
t.nsqd.logf(LOG_ERROR,
"TOPIC(%s) ERROR: failed to write message to backend - %s",
t.name, err)
return err
// If mem-queue-size == 0, avoid memory chan, for more consistent ordering,
// but try to use memory chan for deferred messages (they lose deferred timer
// in backend queue) or if topic is ephemeral (there is no backend queue).
if cap(t.memoryMsgChan) > 0 || t.ephemeral || m.deferred != 0 {
select {
case t.memoryMsgChan <- m:
return nil
default:
break // write to backend
}
}
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I don't think we want to wait around for a second in the ephemeral case - the intention is that it's bounded and lossy, why add back pressure when the queue is full?

My proposal would be to simplify this whole if/else block to:

if cap(t.memoryMsgChan) > 0 || m.deferred != 0 {
		select {
		case t.memoryMsgChan <- m:
			return nil
		default:
			break // write to backend
		}
}

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Yeah, we can pare it all the way down and remove the wait. The 1 second is arbitrary ... the expectation/desire is more like a handful of milliseconds. If there's a burst of messages and a bunch of channels, they can all get through the topic to the channels in just a few milliseconds, instead of having deferred time lost or messages kinda sampled.

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(oh and ephemeral topics don't work at all without the memory chan)

err := writeMessageToBackend(m, t.backend)
t.nsqd.SetHealth(err)
if err != nil {
t.nsqd.logf(LOG_ERROR,
"TOPIC(%s) ERROR: failed to write message to backend - %s",
t.name, err)
return err
}
return nil
}

Expand Down