CURATOR-726: Improve tracing for certain operations

[HoustonPutman]

https://issues.apache.org/jira/browse/CURATOR-726

In Apache Solr, we are trying to refactor all of our custom ZK interaction logic to use Curator. One of the things we do is implement metrics on our interactions with ZK. Curator allows us to do this with Tracing and CuratorListeners. However there are two things that don't give us the information we need.

1. The "Get Children" command trace does not give the information needed for the number of Children fetched.
2. The "Multi Transaction" command trace:
   • The trace does not give the number of commands that are in the transaction, which is something we track currently.
   • The MultiTransaction trace is not an AdvancedTrace, it's a normal Trace for some reason. AdvancedTracerDrivers cannot read regular traces, so we can't even see these. We need to update Curator to use an AdvancedTrace for this command.

Therefore in this PR, I have added the two pieces of information (# of Children fetched and # of transactions) and also converted the MultiTransaciton to use an AdvancedTrace.

[tisonkun]

Thank you!

[kezhuw]

LGTM

I think we probably should trace also opcode in future. The name is not good for programmatical decision.

[HoustonPutman]

I think we probably should trace also opcode in future. The name is not good for programmatical decision.

100% agreed! CuratorEventType already exists, so we can repurpose it for this as well.

[HoustonPutman]

I think we probably should trace also opcode in future. The name is not good for programmatical decision.

100% agreed! CuratorEventType already exists, so we can repurpose it for this as well.

Well that's very frustrating. CuratorEventType is in curator-framework, while OperationTrace is in curator-client, so OperationTrace cannot have a CuratorEventType variable...

[kezhuw]

I think we probably should trace also opcode in future.

I guess this require a bunch of changes and worth a separated issue. Let's leave it for future improvement.