Should we really generate a link_up event after Kytos restart?

[italovalcy]

Since we are loading many information from the database, should we really generate link_up event after Kytos restarts? (and previously the link was already UP)

[viniarck]

@italovalcy, theoretically, we could, but in practice, that turned out to be very challenging due to interface events that can be high frequency ones, which in turn can spike up DB writes, which in turn was also making it harder to ensure thread safety (see issue issue #139) with decent performance while syncing the active state of interfaces and links, there's more detailed information on issue 140.

With that said, the current compromise and trade-off we've made is that all NApps who subscribe to kytos/topology.link_up, can still receive a redundant (in some cases) link_up once a controller restarts. So, NApps like mef_eline still needs to be aware of potentially discarding if it didn't impact whichever high level resource (like EVCs) that's using it. Other than, that @Ktmi on version 2023.1 has enhanced kytos/topology.link_up|link_down to notify only once, but without ensuring after a restart.

Let us know if you've noticed any other undesired side effect or anything else.