'juju status' asks for presence (IsAlive) for each object one-by-one

[John A Meinel]

If you turn on "logging-config=juju.state.presence=TRACE" you can see some interesting information like:
machine-0: 15:50:15 TRACE juju.state.presence [8e869b] got request: presence.reqAlive{key:"m#2", result:(chan bool)(0xc422322a80)} for model
machine-0: 15:50:15 TRACE juju.state.presence [8e869b] Alive("m#2") -> true
machine-0: 15:50:15 TRACE juju.state.presence [8e869b] got request: presence.reqAlive{key:"m#0", result:(chan bool)(0xc42222db20)} for model
machine-0: 15:50:15 TRACE juju.state.presence [8e869b] Alive("m#0") -> true
machine-0: 15:50:15 TRACE juju.state.presence [8e869b] got request: presence.reqAlive{key:"m#1", result:(chan bool)(0xc422322ee0)} for model
machine-0: 15:50:15 TRACE juju.state.presence [8e869b] Alive("m#1") -> true
machine-0: 15:50:15 TRACE juju.state.presence [8e869b] got request: presence.reqAlive{key:"u#ul/11", result:(chan bool)(0xc4212f9d50)} for model
machine-0: 15:50:15 TRACE juju.state.presence [8e869b] Alive("u#ul/11") -> true
machine-0: 15:50:15 TRACE juju.state.presence [8e869b] got request: presence.reqAlive{key:"u#ul/5", result:(chan bool)(0xc421fac2a0)} for model
machine-0: 15:50:15 TRACE juju.state.presence [8e869b] Alive("u#ul/5") -> true
machine-0: 15:50:15 TRACE juju.state.presence [8e869b] got request: presence.reqAlive{key:"u#ul/6", result:(chan bool)(0xc421fac700)} for model
machine-0: 15:50:15 TRACE juju.state.presence [8e869b] Alive("u#ul/6") -> true
machine-0: 15:50:15 TRACE juju.state.presence [8e869b] got request: presence.reqAlive{key:"u#ul/8", result:(chan bool)(0xc422323c70)} for model
machine-0: 15:50:15 TRACE juju.state.presence [8e869b] Alive("u#ul/8") -> true
machine-0: 15:50:15 TRACE juju.state.presence [8e869b] got request: presence.reqAlive{key:"u#ul/3", result:(chan bool)(0xc421facc40)} for model
machine-0: 15:50:15 TRACE juju.state.presence [8e869b] Alive("u#ul/3") -> true
machine-0: 15:50:15 TRACE juju.state.presence [8e869b] got request: presence.reqAlive{key:"u#ul/4", result:(chan bool)(0xc4223345b0)} for model
machine-0: 15:50:15 TRACE juju.state.presence [8e869b] Alive("u#ul/4") -> true
machine-0: 15:50:15 TRACE juju.state.presence [8e869b] got request: presence.reqAlive{key:"u#ul/7", result:(chan bool)(0xc421facf50)} for model
machine-0: 15:50:15 TRACE juju.state.presence [8e869b] Alive("u#ul/7") -> true
machine-0: 15:50:15 TRACE juju.state.presence [8e869b] got request: presence.reqAlive{key:"u#ul/9", result:(chan bool)(0xc422279500)} for model
machine-0: 15:50:15 TRACE juju.state.presence [8e869b] Alive("u#ul/9") -> true
machine-0: 15:50:15 TRACE juju.state.presence [8e869b] got request: presence.reqAlive{key:"u#ul/10", result:(chan bool)(0xc422279c70)} for model
machine-0: 15:50:15 TRACE juju.state.presence [8e869b] Alive("u#ul/10") -> true
machine-0: 15:50:15 TRACE juju.state.presence [8e869b] got request: presence.reqAlive{key:"u#ul/0", result:(chan bool)(0xc4218f8070)} for model
machine-0: 15:50:15 TRACE juju.state.presence [8e869b] Alive("u#ul/0") -> true
machine-0: 15:50:15 TRACE juju.state.presence pingbatcher has 0 pings to record
machine-0: 15:50:15 TRACE juju.state.presence [8e869b] got request: presence.reqAlive{key:"u#ul/1", result:(chan bool)(0xc421fadb20)} for model
machine-0: 15:50:15 TRACE juju.state.presence [8e869b] Alive("u#ul/1") -> true
machine-0: 15:50:15 TRACE juju.state.presence [8e869b] got request: presence.reqAlive{key:"u#ul/2", result:(chan bool)(0xc4218f8540)} for model
machine-0: 15:50:15 TRACE juju.state.presence [8e869b] Alive("u#ul/2") -> true
machine-0: 15:50:15 TRACE juju.state.presence [8e869b] got request: presence.reqAlive{key:"u#peer-xplod/0", result:(chan bool)(0xc4229873b0)} for model
machine-0: 15:50:15 TRACE juju.state.presence [8e869b] Alive("u#peer-xplod/0") -> true
machine-0: 15:50:15 TRACE juju.state.presence [8e869b] got request: presence.reqAlive{key:"u#peer-xplod/1", result:(chan bool)(0xc421468e70)} for model
machine-0: 15:50:15 TRACE juju.state.presence [8e869b] Alive("u#peer-xplod/1") -> true
machine-0: 15:50:15 TRACE juju.state.presence [8e869b] got request: presence.reqAlive{key:"u#peer-xplod/2", result:(chan bool)(0xc422335180)} for model
machine-0: 15:50:15 TRACE juju.state.presence [8e869b] Alive("u#peer-xplod/2") -> true

We're not doing a "sync" for each of these, so its just returning whatever the current cached lifetime is in memory for each object. But it is a fair bit of overhead (creating a channel to return the response on, putting the request into the channel, handling it, returning the values, etc.). It would be better if we asked for the presence information in a large batch with a single return.

[John A Meinel (jameinel)]

https://github.com/jameinel/juju/tree/2.2-presence-multi-1703594

The above branch is a start at changing the presence code to support a batch call of the presence for all agents in one request.

However, apiserver/client/status.go is still written very much as:
 for _, machine := range machines {
    infoForMachine = getStatusInformation(machine)
 }
 for _, app := range applications {
    infoForApp = processApp(app)
 }

So none of that code builds up a list of things to ask about, and then asks about them all at once. So it isn't worth updating Presence until we have a good caller that can actually call it in a meaningful way. Not worth it yet.

[Anastasia (anastasia-macmood)]

We will not be fixing this in 2.2 as there are no further point releases planned in this series.

[Canonical Juju QA Bot (juju-qa-bot)]

This bug has not been updated in 2 years, so we're marking it Low importance. If you believe this is incorrect, please update the importance.