[FEAT] - Only enable ledger events if asked to

[jasagredo]

Describe the feature you'd like

At the moment we enable ledger events unconditionally (search for EPReturn). We then seem to only use them for tracing or testing.

It probably would make sense to make this dependent on some configuration flag so that ledger operations would be even cheaper.

[amesgen]

We then seem to only use them for tracing or testing.

Do you have an example where we use them for tracing? (The InspectLedger stuff doesn't rely on Ledger events.)

It probably would make sense to make this dependent on some configuration flag so that ledger operations would be even cheaper.

There is some discussion on this in this thread on Slack.

In particular, @lehins said there that laziness means that we currently don't pay any additional cost (though this ticket still makes sense):

@amesgen: Just out of interest: In Consensus, we set asoEvents = STS.EPReturn here; however we don't ever look at them, so maybe lazy evaluation saves us?

@lehins: Yeah, laziness saves from expensive computation there. But I'd suggest disabling the events anyways

[jasagredo]

I don't have an example, and indeed I was confused by the InspectLedger stuff. Good catch.

I'm however reading the thread and also this open PR #402 and I wonder if we would like to take this approach further:

• Make ApplySTSOpts configurable
• Allow for events handler to be passed into consensus

That way we could disable events and if they are enabled we could connect a handler to be used by consumers (node?)

[jasagredo]

I did some work on #1390, still as a WIP