consensus_leaders_handler.h

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/* Copyright (c) 2021, 2024, Oracle and/or its affiliates.
 
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   it under the terms of the GNU General Public License, version 2.0,
   as published by the Free Software Foundation.
 
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#ifndef CONSENSUS_LEADERS_HANDLER_INCLUDED
#define CONSENSUS_LEADERS_HANDLER_INCLUDED
 
#include "plugin/group_replication/include/member_info.h"
#include "plugin/group_replication/include/member_version.h"
#include "plugin/group_replication/include/plugin_observers/group_event_observer.h"
#include "plugin/group_replication/libmysqlgcs/include/mysql/gcs/gcs_member_identifier.h"
 
/**
 * @brief Deals with the orchestration necessary to set the appropriate
 * "consensus leaders" on GCS.
 *
 * Reacts to successful primary elections by setting the newly elected primary
 * as the single preferred "consensus leader" in GCS.
 */
class Consensus_leaders_handler : public Group_event_observer {
 public:
  /**
   * Register as a group event observer in @c group_events_manager.
   *
   * @param group_events_manager
   */
  Consensus_leaders_handler(
      Group_events_observation_manager &group_events_manager);
 
  /**
   * Unregister as a group event observer from @c m_group_events_manager.
   */
  ~Consensus_leaders_handler() override;
 
  int after_view_change(const std::vector<Gcs_member_identifier> &joining,
                        const std::vector<Gcs_member_identifier> &leaving,
                        const std::vector<Gcs_member_identifier> &group,
                        bool is_leaving, bool *skip_election,
                        enum_primary_election_mode *election_mode,
                        std::string &suggested_primary) override;
 
  /**
   * @brief Sets the newly elected primary as the single preferred "consensus
   * leader" in GCS.
   *
   * @param primary_uuid the elected primary
   * @param primary_change_status if the primary changed after the election
   * @param election_mode what was the election mode
   * @param error if there was and error on the process
   * @return int 0 on success
   */
  int after_primary_election(
      std::string primary_uuid,
      enum_primary_election_primary_change_status primary_change_status,
      enum_primary_election_mode election_mode, int error) override;
 
  int before_message_handling(const Plugin_gcs_message &message,
                              const std::string &message_origin,
                              bool *skip_message) override;
 
  /**
   * @brief Set the appropriate "consensus leaders" in GCS.
   *
   * The "consensus leaders" are set according to the following rules:
   * 0) If the the return result  of allow_single_leader_getter lambda is false
   *    :do nothing
   * a) @c communication_protocol is < 8.0.27: do nothing
   * b) @c communication_protocol is >= 8.0.27:
   *    b1) @c primary_mode is SINGLE and @c my_role is PRIMARY: set myself,
   *        @c my_gcs_id, as the single preferred "consensus leader"
   *    b2) @c primary_mode is SINGLE and @c my_role is SECONDARY: do nothing
   *    b3) @c primary_mode is MULTI: set everyone as "consensus leader"
   *
   * @param communication_protocol
   * @param is_single_primary_mode
   * @param role
   * @param my_gcs_id
   * @param allow_single_leader_getter
   */
  void set_consensus_leaders(Member_version const &communication_protocol,
                             bool is_single_primary_mode,
                             Group_member_info::Group_member_role role,
                             Gcs_member_identifier const &my_gcs_id,
                             std::function<bool()> allow_single_leader_getter);
 
  /**
   * @brief Set the appropriate "consensus leaders" in GCS.
   *
   * The "consensus leaders" are set according to the following rules:
   * a) @c communication_protocol is < 8.0.27: do nothing
   * b) @c communication_protocol is >= 8.0.27:
   *    b1) @c primary_mode is SINGLE and @c my_role is PRIMARY: set myself,
   *        @c my_gcs_id, as the single preferred "consensus leader"
   *    b2) @c primary_mode is SINGLE and @c my_role is SECONDARY: do nothing
   *    b3) @c primary_mode is MULTI: set everyone as "consensus leader"
   *
   * It inserts a default implementation of allow_single_leader_getter that
   * verifies the current value of group_replication_paxos_single_leader var
   *
   * @param communication_protocol
   * @param is_single_primary_mode
   * @param role
   * @param my_gcs_id
   */
  void set_consensus_leaders(Member_version const &communication_protocol,
                             bool is_single_primary_mode,
                             Group_member_info::Group_member_role role,
                             Gcs_member_identifier const &my_gcs_id);
 
 private:
  void set_as_single_consensus_leader(
      Gcs_member_identifier const &leader) const;
  void set_everyone_as_consensus_leader() const;
 
  static Member_version const
      s_first_protocol_with_support_for_consensus_leaders;
  Group_events_observation_manager &m_group_events_manager;
};
 
#endif /* CONSENSUS_LEADERS_HANDLER_INCLUDED */