Downgrade Retry policies in Cassandra using nodejs

downgradeRetryPolicy.js

/**
 * DowngradeRetryPolicy - This module is used to retry the READ / WRITE operation
 * by downgrading the value of consistency to minimum value.
 * @constructor
 */
function DowngradeRetryPolicy() {
}

// Inherit the retry policy 
util.inherits(DowngradeRetryPolicy, RetryPolicy);

/** 
 * In case of node unavailability, this function will be triggered and the consisteny level is updated and tried again. 
 * 
 * @param {OperationInfo} info
 * @param {Number} consistency The [consistency]{@link module:types~consistencies} level of the query that triggered
 * the exception.
 * @param {Number} required The number of replicas whose response is required to achieve the
 * required [consistency]{@link module:types~consistencies}.
 * @param {Number} alive The number of replicas that were known to be alive when the request had been processed
 * (since an unavailable exception has been triggered, there will be alive < required)
 * 
 * @returns {DecisionInfo}
 */
DowngradeRetryPolicy.prototype.onUnavailable = function (info, consistency, required, alive) {
   console.log('consistency',consistency);

   // Initialization
   var currentRetry = info.nbRetry;
   var totalRetry = 2;
   var minimumConsistency = 1;

   console.log('OnUnavailable - retry : ', currentRetry);
   console.log('Total Retries Made : ', currentRetry);
   console.log('Total number of Replicas alive : ', alive);

   if (currentRetry > totalRetry) {
 return this.rethrowResult();
   } else if(alive == minimumConsistency) {
     console.log('Retries with Minimum consistency', minimumConsistency);
     return this.retryResult(minimumConsistency, true);
   }

};

/**
 * On Read Timeout, this function will check whether to reduce the consistency level and retry.
 */
DowngradeRetryPolicy.prototype.onReadTimeout = function (info, consistency, received, blockFor, isDataPresent) {

  // Initialization
  var totalRetry = 2;
  var currentRetry = info.nbRetry;
  var minimumConsistency = 1;

  console.log('OnRead Timeout - retry :', currentRetry);

  if (currentRetry > totalRetry) {
    return this.rethrowResult();
  } else if (received == minimumConsistency) {
    // Retries with the minimum consistency
    console.log('Retries with Minimum consistency', minimumConsistency);
    return this.retryResult(minimumConsistency, true);
  }
};

/**
 * On Write Timeout, this function will check whether to reduce the consistency level and retry.
 */
DowngradeRetryPolicy.prototype.onWriteTimeout = function (info, consistency, received, blockFor, writeType) {
  // Initializatio
  var totalRetry = 2;
  var currentRetry = info.nbRetry;
  var minimumConsistency = 1;

  console.log('OnWrite Timeout - retry : ', currentRetry);

  if (currentRetry > totalRetry) {
return this.rethrowResult();
  } else if (received == minimumConsistency) {
    // Retries with the minimum consistency
    console.log('Retries with Minimum consistency', minimumConsistency);
    return this.retryResult(minimumConsistency, true);
  }
};

/**
 * Returns a {@link DecisionInfo} to callback in error when a err is obtained for a given request.
 * @returns {DecisionInfo}
 */
DowngradeRetryPolicy.prototype.rethrowResult = function () {
  return { decision: DowngradeRetryPolicy.retryDecision.rethrow };
};

/**
 * Method which frame the Retry Policy paramters. 
 */
DowngradeRetryPolicy.prototype.retryResult = function (consistency, useCurrentHost) {
  console.log('Retry Result consistency : ' + consistency);
  console.log('current host : ', useCurrentHost);
  return {
    decision: RetryPolicy.retryDecision.retry,
    consistency: consistency,
    useCurrentHost: useCurrentHost !== false
  };
};

/**
 * Determines the retry decision for the retry policies.
 * @type {Object}
 * @property {Number} rethrow
 * @property {Number} retry
 * @property {Number} ignore
 * @static
 */
DowngradeRetryPolicy.retryDecision = {
  rethrow:  0,
  retry:    1,
  ignore:   2
};