the-algorithm/src/java/com/twitter/search/earlybird_root/EarlybirdTierThrottleDeciders.java

package com.twitter.search.earlybird_root;

import javax.inject.Inject;
import javax.inject.Singleton;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.twitter.search.common.decider.SearchDecider;

/**
 * Controls fractions of requests that are sent out to each tier.
 */
@Singleton
public class EarlybirdTierThrottleDeciders {
  private static final Logger LOG =
      LoggerFactory.getLogger(EarlybirdTierThrottleDeciders.class);
  private static final String TIER_THROTTLE_DECIDER_KEY_FORMAT =
      "percentage_to_hit_cluster_%s_tier_%s";
  private final SearchDecider decider;

  /**
   * Construct a decider using the singleton decider object injected by Guice for the
   * specified tier.
   * See {@link com.twitter.search.common.root.SearchRootModule#provideDecider()}
   */
  @Inject
  public EarlybirdTierThrottleDeciders(SearchDecider decider) {
    this.decider = decider;
  }

  /**
   * Return the throttle decider key for the specified tier.
   */
  public String getTierThrottleDeciderKey(String clusterName, String tierName) {
    String deciderKey = String.format(TIER_THROTTLE_DECIDER_KEY_FORMAT, clusterName, tierName);
    if (!decider.getDecider().feature(deciderKey).exists()) {
      LOG.warn("Decider key {} not found. Will always return unavailable.", deciderKey);
    }
    return deciderKey;
  }

  /**
   * Check whether a request should be sent to the specified tier.
   */
  public Boolean shouldSendRequestToTier(final String tierDarkReadDeciderKey) {
    return decider.isAvailable(tierDarkReadDeciderKey);
  }
}