Re: [yang-doctors] [Netconf] Yangdoctors last call review of draft-ietf-netconf-subscribed-notifications-10
"Eric Voit (evoit)" <evoit@cisco.com> Mon, 16 April 2018 19:19 UTC
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From: "Eric Voit (evoit)" <evoit@cisco.com>
To: Martin Bjorklund <mbj@tail-f.com>
CC: "andy@yumaworks.com" <andy@yumaworks.com>, "yang-doctors@ietf.org" <yang-doctors@ietf.org>, "draft-ietf-netconf-subscribed-notifications.all@ietf.org" <draft-ietf-netconf-subscribed-notifications.all@ietf.org>, "ietf@ietf.org" <ietf@ietf.org>, "netconf@ietf.org" <netconf@ietf.org>
Thread-Topic: [Netconf] Yangdoctors last call review of draft-ietf-netconf-subscribed-notifications-10
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Date: Mon, 16 Apr 2018 19:19:06 +0000
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Subject: Re: [yang-doctors] [Netconf] Yangdoctors last call review of draft-ietf-netconf-subscribed-notifications-10
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Hi Martin, > Hi, > > "Eric Voit (evoit)" <evoit@cisco.com> wrote: > > > From: Martin Bjorklund, April 6, 2018 10:31 AM > > > > > > Hi, > > > > > > "Eric Voit (evoit)" <evoit@cisco.com> wrote: > > > > Hi Martin, > > > > > > > > After reflecting on this for a bit, I am ok with your argument > > > > that if the system is quickly generating notification-messages, > > > > then the replay buffer might be continuously emptying. And > > > > therefore a hint for replay start time might not be accurate for > > > > very long. As a result, it is better to start the replay > > > > immediately with the oldest buffered event. > > > > > > > > I have updated the establish-subscription RPC as follows. Does > > > > this cover your concern (per this sub-thread)? > > > > > > > > rpc establish-subscription { > > > > input { } > > > > output { > > > > leaf identifier { } > > > > leaf replay-start-time { > > > > if-feature "replay"; > > > > type yang:date-and-time; > > > > description > > > > "If a replay has been requested, this represents the > > > > earliest time covered by the event buffer for the requested > > > > stream. The value of this object is the > > > > 'replay-log-aged-time' if it exists. Otherwise it is the > > > > 'replay-log-creation-time'. All buffered event records > > > > after this time will be replayed to a receiver. Note that > > > > this object will only be sent if the 'replay-start-time' is > > > > later than the time requested by the subscriber."; > > > > > > I am ok with this. But the output leaf should probably not have the > > > same name as the input leaf; it is not clear which one you refer to > > > in the last sentence in the description. > > > > Done. It is now: > > > > rpc establish-subscription {... > > output { > > leaf identifier { } > > leaf replay-start-time-revision { > > if-feature "replay"; > > type yang:date-and-time; > > description > > "If a replay has been requested, this represents the > > earliest time covered by the event buffer for the requested > > stream. The value of this object is the > > 'replay-log-aged-time' if it exists. Otherwise it is the > > 'replay-log-creation-time'. All buffered event records > > after this time will be replayed to a receiver. > > This object will only be sent if the start time has been > > revised to be later than the time requested by the > > subscriber."; > > } > > } > > } > > > > > Also, I suggest you do: > > > > > > s/Note that this/This/ > > > > > > in the last sentence. > > > > Done > > I noted that this change did not make it into -11. It is in the next version. You can see it here: https://github.com/netconf-wg/rfc5277bis/blob/master/draft-ietf-netconf-subscribed-notifications-12.txt > > > Reading the definition of 'replay-log-aged-time' again, it says: > > > > > > The timestamp of the last event record aged out of the log. > > > > > > The document doesn't define what "the timestamp" of an event record > > > is. > > > Is this the time that is sent in the "eventTime" field in the > > > <notification>? I think this needs to be clarified. > > > > How about: > > > > leaf replay-log-aged-time { > > if-feature "replay"; > > type yang:date-and-time; > > description > > "The timestamp associated with last event record which has > > been aged out of the log. This timestamp identifies how far > > back into history this replay log extends, if it doesn't > > extend back to the 'replay-log-creation-time'. This object > > MUST be present if replay is supported and any event records > > have been aged out of the log."; > > } > > > > > > To complement this description, in the "Event Record Delivery" > > section, I placed the following sentence after the example RFC 5277 > > notification: > > > > "In the figure above, the "eventTime" is populated with a timestamp > > matching the time an originating process identified as when this event > > occurred." > > I think you need to explain this in more general terms than just in an > example of a 5277 notification. Specifically, I think you should introduce a > generic term for when an event record is generated (maybe "event creation > time", or even "event timestamp"), and then use this term consistently, and > also explain in section 2.6 that the 5277 "eventTime" element contains the > "event timestamp". Added the term: Event occurrence time: a timestamp matching the time an originating process identified as when an event happened. In the Terminology section. In the "Event Record Delivery" Section, the text before the example now says: This notification message MUST be encoded in a <notification> message as defined within [RFC5277], Section 4. And per [RFC5277]'s "eventTime" object definition, the "eventTime" is populated with the event occurrence time. Updated subscribed-notification document can be seen at: https://github.com/netconf-wg/rfc5277bis/blob/master/draft-ietf-netconf-subscribed-notifications-12.txt Also imported the "event occurrence time" text into the notification-messages draft. Eric > Then this term should be imported by > draft-ietf-netconf-notification-messages and used there as well. > > > /martin > > > > > > Eric > > > > > /martin > > > > > > > > > > > > > } > > > > } > > > > } > > > > > > > > If you are ok, I will spread the change through the rest of the > > > > document. > > > > > > > > Eric > > > > > > > > > > > > > "Eric Voit (evoit)" <evoit@cisco.com> wrote: > > > > > > > From: Martin Bjorklund, March 23, 2018 7:37 AM > > > > > > > > > > > > > > Hi, > > > > > > > > > > > > > > > > > > > > > "Eric Voit (evoit)" <evoit@cisco.com> wrote: > > > > > > > > Hi Martin, > > > > > > > > > > > > > > > > > From: Martin Bjorklund, March 16, 2018 4:19 AM > > > > > > > > > > > > > > > > > > Hi, > > > > > > > > > > > > > > > > > > Andy Bierman <andy@yumaworks.com> wrote: > > > > > > > > > > > > > > > > > > [...] > > > > > > > > > > > > > > > > > > > 2.4.2.1. Replay Subscription > > > > > > > > > > > > > > > > > > > > If the "replay-start- > > > > > > > > > > time" contains a value that is earlier than content stored > > > > > > > > > > within > > > > > > > > > > the > > > > > > > > > > publisher's replay buffer, then the subscription > > > > > > > > > > MUST be > > > > > rejected, > > > > > > > > > > and the leaf "replay-start-time-hint" MUST be set > > > > > > > > > > in the > > > reply. > > > > > > > > > > > > > > > > > > > > >> this is a significant and bad change from RFC > > > > > > > > > > 5277 > > > behavior > > > > > > > > > > >> the start-time says "send all events that you have > > > > > > > > > > >> stored > > > > > > > > > > since this time" The server sends its oldest event and > > > > > > > > > > does > > > > > > > > > > not reject the request. This draft incorrectly > > > > > > > > > > interprets > > > > > > > > > > the request as "the server MUST have an event > > > > > > > > > > stored at > > > least > > > > > > > > > > this old" > > > > > > > > > > > > > > > > > > I agree, and I have pointed this out in earlier reviews. > > > > > > > > > > > > > > > > In our past discussions, it looked like you were ok after > > > > > > > > reading Yves requirement here: > > > > > > > > > > > > > > > > https://www.ietf.org/mail- > > > > > archive/web/netconf/current/msg12154.htm > > > > > > > > l > > > > > > > > > > > > > > > > Beyond this functional requirement, the design pattern > > > > > > > > used is that an establish-subscription RPC must send the > > > > > > > > exact parameters accepted by the publisher. > > > > > > > > > > > > > > > > > > > > > > > > > If a client sends a too early time, and the server > > > > > > > > > doesn't send the optional hint, the client will have to > > > > > > > > > guess the time. Not very robust. > > > > > > > > > > > > > > > > > > If the motivation is that the client should be informed > > > > > > > > > that he might have missed some notifs b/c the > > > > > > > > > replay-start-time is too early, this information can be > > > > > > > > > passed in the rpc-reply from establish-subscription instead. > > > > > > > > > > > > > > > > Yes this could be done. But this doesn't follow the > > > > > > > > design pattern of making the client explicitly ask for what they > want. > > > > > > > > Consistent design patterns do matter. > > > > > > > > > > > > > > Well, "what they want" depends on the semantics of this leaf! > > > > > > > If we keep the old semantics, then if the client passes this > > > > > > > parameter with some start time, it "explicitly asked for > > > > > > > what it > > > wanted". > > > > > > > > > > > > > > Anyway, if the objective is to ensure that no notifs are > > > > > > > sent unless the replay-start-time exactly matches the > > > > > > > event-time of a notification in the buffer, then we can add > > > > > > > a parameter to ensure that. > > > > > > > > > > > > The current definition of replay-start-time is: > > > > > > > > > > > > "Used to trigger the replay feature and indicate that the > > > > > > replay should start at the time specified..." > > > > > > > > > > > > To me, that means the replay-start-time has to be covered by > > > > > > the scope of the replay buffer. It does not mean that it is > > > > > > required that the requested replay-start-time needs to exactly > > > > > > match the time of a buffered event. > > > > > > > > > > The text is quite unclear: > > > > > > > > > > Used to trigger the replay feature and indicate that the > > > > > replay should start at the time specified. > > > > > > > > > > and: > > > > > > > > > > If the "replay-start- time" contains a value that is earlier than > > > > > content stored within the publisher's replay buffer, then the > > > > > subscription MUST be rejected > > > > > > > > > > In lack of a clear definition, I assume that "content stored > > > > > [in] replay buffer" > > > > > refers to event records, since I assume that nothing else can be > > > > > stored in the replay buffer? > > > > > > > > > > Next question is what it means that a time value is earlier than > > > > > "content"? > > > > > Again, my assumption is that it means "earlier than the 'eventTime' > > > > > of the event records". Is this not what is intended? > > > > > > > > > > From what you write here though, I think that what you propose > > > > > is > > > > > that: > > > > > > > > > > If "replay-start-time" is less than the latest of > > > > > "replay-log-aged-time" and "replay-log-creation-time", then the > > > > > request is rejected. > > > > > > > > > > This must be clarified. Also, ensure that the required behavior > > > > > is clearly defined in the YANG module, and not just in the text > > > > > in the document. > > > > > > > > > > But I still think that there should be some way for the client > > > > > to get all buffered event records, just like what was supported > > > > > in RFC 5277, without extra round trips. Note that if the system > > > > > is quickly generating notifs, the client might need many round > > > > > trips before it manages to replay anything. > > > > > > > > > > > > > > > > > In all cases, if the client receives a notif with a time > > > > > > > later than what it asked for, it knows that it might have > > > > > > > lost some notifs. > > > > > > > > > > > > Why would this mean it might have lost some notifs? In the > > > > > > current embodiment, the replay will not start unless the > > > > > > subscriber asked for a time that is within the scope covered > > > > > > by the buffer. I.e., a time later than both "replay-log-creation- > time" > > > > > > and > > > "replay-log-aged-time". > > > > > > > > > > See above. But the reason for rejection is that the client > > > > > might have lost some notifs. > > > > > > > > > > > > leaf replay-exact-start-time { > > > > > > > if-feature "replay"; > > > > > > > when "../replay-start-time"; > > > > > > > type empty; > > > > > > > description > > > > > > > "If this parameter is present, and the server does not have > > > > > > > any > > > > > > > stored event record with 'eventTime' equal to the requested > > > > > > > 'replay-start-time', then the server MUST reject the > > > > > > > request."; > > > > > > > } > > > > > > > > > > If we add something like this, the leaf name and description > > > > > text needs to be tweaked for the clarified semantics of > > > > > replay-start-time. > > > > > > > > > > > Something like this parameter *might* be applicable if we > > > > > > choose to respond to a dynamic replay request with events > > > > > > later than those requested. (i.e., in the > > > > > > establish-subscription success > > > > > > response.) As noted in other threads, this is a legitimate way > > > > > > to approach the issue. However if the WG chooses this way, > > > > > > this will result in an exception to the design pattern of > > > > > > requiring the subscriber to ask for what they are going to receive. > > > > > > > > > > I disagree. The client explicitly asks the server to send all > > > > > buffered event records. > > > > > > > > > > > In addition, we might end up sending a stream of information > > > > > > to the subscriber which is not sufficient, and therefore not > > > > > > verifiably relevant. > > > > > > > > > > It is up to the client to define what is relevant. Maybe I just > > > > > want to view the replay buffer for trouble shooting purposes. > > > > > > > > > > > > > > > > > > > > /martin > > > > > >
- [yang-doctors] Yangdoctors last call review of dr… Andy Bierman
- Re: [yang-doctors] [Netconf] Yangdoctors last cal… Martin Bjorklund
- Re: [yang-doctors] Yangdoctors last call review o… Eric Voit (evoit)
- Re: [yang-doctors] [Netconf] Yangdoctors last cal… Eric Voit (evoit)
- Re: [yang-doctors] [Netconf] Yangdoctors last cal… Martin Bjorklund
- Re: [yang-doctors] [Netconf] Yangdoctors last cal… Martin Bjorklund
- Re: [yang-doctors] [Netconf] Yangdoctors last cal… Andy Bierman
- Re: [yang-doctors] [Netconf] Yangdoctors last cal… Andy Bierman
- Re: [yang-doctors] [Netconf] Yangdoctors last cal… Eric Voit (evoit)
- Re: [yang-doctors] [Netconf] Yangdoctors last cal… Eric Voit (evoit)
- Re: [yang-doctors] [Netconf] Yangdoctors last cal… Martin Bjorklund
- Re: [yang-doctors] [Netconf] Yangdoctors last cal… Martin Bjorklund
- Re: [yang-doctors] [Netconf] Yangdoctors last cal… Eric Voit (evoit)
- Re: [yang-doctors] [Netconf] Yangdoctors last cal… Eric Voit (evoit)
- Re: [yang-doctors] [Netconf] Yangdoctors last cal… Martin Bjorklund
- Re: [yang-doctors] [Netconf] Yangdoctors last cal… Eric Voit (evoit)
- Re: [yang-doctors] [Netconf] Yangdoctors last cal… Martin Bjorklund
- Re: [yang-doctors] [Netconf] Yangdoctors last cal… Eric Voit (evoit)