question

Hello @wederbrand, thank you for leveraging the community portal for your question/needs!

I am assuming you're using the latest DataStax Java Driver 4.10.0 here as that wasn't specified in the original question.

Here is a snippet with which you could enable speculative execution for your application needs. Remember that it will only be in operation if your queries are idempotent. For more details, read the documentation here.

import com.datastax.oss.driver.api.core.CqlSession;
import com.datastax.oss.driver.api.core.CqlSessionBuilder;
import com.datastax.oss.driver.api.core.config.DefaultDriverOption;
import com.datastax.oss.driver.api.core.config.DriverConfigLoader;
import com.datastax.oss.driver.api.core.config.ProgrammaticDriverConfigLoaderBuilder;

public class ProgrammaticDriverConfig {
    public static void main(String... args) {
ProgrammaticDriverConfigLoaderBuilder driverBldr = DriverConfigLoader.programmaticBuilder();
driverBldr
.withString(DefaultDriverOption.SPECULATIVE_EXECUTION_POLICY_CLASS,
"ConstantSpeculativeExecutionPolicy")
.withInt(DefaultDriverOption.SPECULATIVE_EXECUTION_MAX, 3)
.withDuration(DefaultDriverOption.SPECULATIVE_EXECUTION_DELAY, Duration.ofMillis(100));
CqlSessionBuilder cqlSessionBuilder = CqlSession.builder().withKeyspace("")
.withConfigLoader(driverBldr.build());
    }
}

Given the above configuration, an idempotent query would be handled this way:

• start the initial execution at t0;

• if no response has been received at t0 + 100 milliseconds, start a speculative execution on another node;

• if no response has been received at t0 + 200 milliseconds, start another speculative execution on a third node;

• past that point, don’t query other nodes, just wait for the first response to arrive.

Cheers!