KandraMultiDc

Multi-datacenter extension for Kandra.

Include kandra-multidc in your dependencies for multi-DC features:

• Token-aware load balancing with DC failover

• Per-operation consistency level control

• Speculative execution for latency-sensitive reads

• LWT serial consistency configuration for globally unique constraints

All multi-DC configuration lives in KandraConfig blocks:

install(Kandra) {
    localDatacenter = "us-east-1"

    consistency {
        defaultRead = KandraConsistency.LOCAL_ONE
        defaultWrite = KandraConsistency.LOCAL_QUORUM
    }

    loadBalancing {
        tokenAware = true
        dcAwareFailover = true
        allowedRemoteDcs = listOf("eu-west-1", "ap-southeast-1")
    }

    failover {
        onLocalDcUnavailable = FailoverPolicy.RETRY_REMOTE_DC
        remoteRetryDelayMs = 100
    }

    speculativeExecution {
        enabled = true
        delayMillis = 100
        maxAttempts = 2
    }
}

LWT serial consistency

Use LOCAL_SERIAL (default) for Paxos within the local DC only — sufficient for region-scoped uniqueness (e.g. wallet creation per-region).

Use SERIAL for globally unique constraints (e.g. usernames unique across all DCs):

// Global uniqueness — Paxos consensus across ALL DCs
val registered = userRepo.saveIfNotExists(user, serialConsistency = KandraConsistency.SERIAL)

Speculative execution

Only idempotent statements are eligible for speculative execution. Kandra automatically sets isIdempotent = false on plain INSERT, collection mutations, and counter updates — the driver skips speculative execution for them.