feat: failover2

[sophia-bq]

Summary

Description

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[karenc-bq]

computeIfAbsent will check the map and create the item for the given key if item doesn't already exist. I don't think we need to call get here, then call computeIfAbsent in initMonitor. This implementation will check the map twice.

You could just call computeIfAbsent directly here

    const monitor: ClusterTopologyMonitor = MonitoringRdsHostListProvider.monitors.computeIfAbsent(
      this.clusterId,
      (x) =>
        new ClusterTopologyMonitorImpl(
          this.clusterId,
          MonitoringRdsHostListProvider.topologyCache,
          this.initialHost,
          this.properties,
          this.pluginService,
          this,
          WrapperProperties.CLUSTER_TOPOLOGY_REFRESH_RATE_MS.get(this.properties),
          WrapperProperties.CLUSTER_TOPOLOGY_HIGH_REFRESH_RATE_MS.get(this.properties)
        ),
      MonitoringRdsHostListProvider.MONITOR_EXPIRATION_NANOS
    );

[karenc-bq]

Need to update the error message to use BlockingHostListProvider instead of MonitoringRdsHostListProvider

[karenc-bq]

I don't think you need to cast it.

Suggested change

	const updatedHostList: HostInfo[] = await (hostListProvider as MonitoringRdsHostListProvider).forceMonitoringRefresh(
	shouldVerifyWriter,
	timeoutMs
	);
	const updatedHostList: HostInfo[] = await hostListProvider.forceMonitoringRefresh(shouldVerifyWriter, timeoutMs);

If you really need to cast it, use the interface not the implementation.

[karenc-bq]

No longer used in the code, could remove this and relevant unit tests

[karenc-bq]

Suggested change

	// Call was initiated by Failover2 Plugin, does not require additional processing.
	if (props.has(Failover2Plugin.INTERNAL_CONNECT_PROPERTY_NAME)) {
	return await this._staleDnsHelper.getVerifiedConnection(hostInfo.host, isInitialConnection, this.hostListProviderService!, props, connectFunc);
	}
	// Failover is not enabled, does not require additional processing.
	if (!this.enableFailoverSetting || !WrapperProperties.ENABLE_CLUSTER_AWARE_FAILOVER.get(props)) {
	return await this._staleDnsHelper.getVerifiedConnection(hostInfo.host, isInitialConnection, this.hostListProviderService!, props, connectFunc);
	}
	if (
	// Call was initiated by Failover2 Plugin, does not require additional processing.
	props.has(Failover2Plugin.INTERNAL_CONNECT_PROPERTY_NAME) ||
	// Failover is not enabled, does not require additional processing.
	!this.enableFailoverSetting ||
	!WrapperProperties.ENABLE_CLUSTER_AWARE_FAILOVER.get(props)
	) {
	return await this._staleDnsHelper.getVerifiedConnection(hostInfo.host, isInitialConnection, this.hostListProviderService!, props, connectFunc);
	}

Can we merge the checks to reduce code duplication

[karenc-bq]

this._isInTransaction is set via this.pluginService.isInTransaction(), and when we use it we check this.pluginService.isInTransaction() anyway. Not sure if it is worth having this local variable.

[karenc-bq]

Can we refactor this logic into a method to reduce duplicated code

  private logAndThrowError(errorMessage: string) {
    logger.error(errorMessage);
    this.failoverWriterFailedCounter.inc();
    throw new FailoverFailedError(errorMessage);
  }