4.x: Add rack awareness to default load balancing policy

[Gor027]

The default load balancing policy will prefer replicas that are in the local datacenter and in the local rack.
The rack awareness feature is optional, to enable it a local rack should be supplied through configuration by defining the option DefaultDriverOption.LOAD_BALANCING_LOCAL_RACK
basic.load-balancing-policy.local-rack, otherwise it will be disabled and unlike the local datacenter it will not be implicitly fetched from the provided contact points.

[mykaul]

Any updates?

[Gor027]

@avelanarius Ping.

[roydahan]

I think that the tests part should be extended a bit to include more cases.

[malah-akh]

Hello team,

Are we going to release it in the next 3 days?

[avelanarius]

LGTM, I also did some additional manual testing with 12-node, 3 datacenter, 6 rack cluster and it all worked correctly.

[avelanarius]

Hello team,

Are we going to release it in the next 3 days?

@ricardoborenstein
Yes.

Although we have some tests in this PR and I did manual testing, we'll try to do some more testing in the coming 3 days before the release.

[roydahan]

@avelanarius when you have the time, can you please share the results of the tests and/or how you tell if it works or not.
It may help @fruch later when he adds some SCT scenarios for this.

[avelanarius]

Hello team,

Are we going to release it in the next 3 days?

4.15.0.1 is now released, which contains this feature. Relevant docs about the feature: https://java-driver.docs.scylladb.com/stable/manual/core/load_balancing/index.html#rack-awareness

[avelanarius]

@ricardoborenstein ^

[fruch]

@avelanarius is anyone taking it to cassandra-stress ? (or the equivalent 3.x version ?)