replication.h

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/* Copyright (c) 2008, 2023, Oracle and/or its affiliates.
 
   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License, version 2.0,
   as published by the Free Software Foundation.
 
   This program is also distributed with certain software (including
   but not limited to OpenSSL) that is licensed under separate terms,
   as designated in a particular file or component or in included license
   documentation.  The authors of MySQL hereby grant you an additional
   permission to link the program and your derivative works with the
   separately licensed software that they have included with MySQL.
 
   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License, version 2.0, for more details.
 
   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA */
 
#ifndef REPLICATION_H
#define REPLICATION_H
 
#include "my_thread_local.h"         // my_thread_id
#include "mysql/psi/mysql_thread.h"  // mysql_mutex_t
#include "rpl_context.h"
#include "sql/handler.h"  // enum_tx_isolation
 
struct MYSQL;
 
#ifdef __cplusplus
class THD;
#define MYSQL_THD THD *
#else
#define MYSQL_THD void *
#endif
 
#ifdef __cplusplus
extern "C" {
#endif
 
/**
  Struct to share server ssl variables
*/
struct st_server_ssl_variables {
  char *ssl_ca;
  char *ssl_capath;
  char *tls_version;
  char *tls_ciphersuites;
  char *ssl_cert;
  char *ssl_cipher;
  char *ssl_key;
  char *ssl_crl;
  char *ssl_crlpath;
  unsigned int ssl_fips_mode;
 
  void init();
 
  void deinit();
};
 
/**
   Transaction observer flags.
*/
enum Trans_flags {
  /** Transaction is a real transaction */
  TRANS_IS_REAL_TRANS = 1
};
 
/**
 This represents table metadata involved in a transaction
 */
typedef struct Trans_table_info {
  const char *table_name;
  uint number_of_primary_keys;
  /// The db_type of the storage engine used by the table
  int db_type;
  /// information to store if the table has foreign key with 'CASCADE' clause.
  bool has_cascade_foreign_key;
} Trans_table_info;
 
/**
  This represents some of the context in which a transaction is running
  It summarizes all necessary requirements for Group Replication to work.
 
  These requirements might be extracted in two different moments in time, and,
  as such, with different contexts:
  - Startup verifications, that are extracted when Group Replication starts,
    and typically from global vars.
  - Runtime verifications, that are extracted when a transaction is running. It
    it typically from session THD vars or from mutable global vars.
 
  Please refer to the place where information is extracted for more details
  about it.
 */
typedef struct Trans_context_info {
  bool binlog_enabled;
  ulong gtid_mode;  // enum values in Gtid_mode::value_type
  bool log_replica_updates;
  ulong binlog_checksum_options;  // enum values in enum
                                  // enum_binlog_checksum_alg
  ulong binlog_format;            // enum values in enum enum_binlog_format
  // enum values in enum_transaction_write_set_hashing_algorithm
  ulong transaction_write_set_extraction;
  ulong mi_repository_type;   // enum values in enum_info_repository
  ulong rli_repository_type;  // enum values in enum_info_repository
  // enum values in enum_mts_parallel_type
  ulong parallel_applier_type;
  ulong parallel_applier_workers;
  bool parallel_applier_preserve_commit_order;
  enum_tx_isolation tx_isolation;  // enum values in enum_tx_isolation
  uint lower_case_table_names;
  bool default_table_encryption;
} Trans_context_info;
 
/**
  This represents the GTID context of the transaction.
 */
typedef struct Trans_gtid_info {
  ulong type;         // enum values in enum_gtid_type
  int sidno;          // transaction sidno
  long long int gno;  // transaction gno
} Trans_gtid_info;
 
class Binlog_cache_storage;
/**
   Transaction observer parameter
*/
typedef struct Trans_param {
  uint32 server_id;
  const char *server_uuid;
  my_thread_id thread_id;
  uint32 flags;
 
  /*
    The latest binary log file name and position written by current
    transaction, if binary log is disabled or no log event has been
    written into binary log file by current transaction (events
    written into transaction log cache are not counted), these two
    member will be zero.
  */
  const char *log_file;
  my_off_t log_pos;
 
  /*
    Transaction GTID information.
  */
  Trans_gtid_info gtid_info;
 
  /*
    Set on before_commit hook.
  */
  Binlog_cache_storage *trx_cache_log;
  Binlog_cache_storage *stmt_cache_log;
  ulonglong cache_log_max_size;
  /*
    The flag designates the transaction is a DDL contained is
    the transactional cache.
  */
  bool is_atomic_ddl;
 
  /*
   This is the list of tables that are involved in this transaction and its
   information
   */
  Trans_table_info *tables_info;
  uint number_of_tables;
 
  /*
   Context information about system variables in the transaction
   */
  Trans_context_info trans_ctx_info;
 
  /// pointer to the status var original_commit_timestamp
  unsigned long long *original_commit_timestamp;
 
  /** Replication channel info associated to this transaction/THD */
  enum_rpl_channel_type rpl_channel_type;
 
  /** contains the session value of group_replication_consistency */
  ulong group_replication_consistency;
 
  /** value of session wait_timeout, timeout to hold transaction */
  ulong hold_timeout;
 
  /// pointer to original_server_version
  uint32_t *original_server_version;
 
  /// pointer to immediate_server_version
  uint32_t *immediate_server_version;
 
  /*
    Flag to identify a 'CREATE TABLE ... AS SELECT'.
  */
  bool is_create_table_as_query_block;
 
  /// pointer to server THD
  THD *thd;
} Trans_param;
 
/**
   Transaction observer parameter initialization.
*/
#define TRANS_PARAM_ZERO(trans_param_obj) \
  memset(&trans_param_obj, 0, sizeof(Trans_param));
 
typedef int (*before_dml_t)(Trans_param *param, int &out_val);
 
/**
  This callback is called before transaction commit
 
  This callback is called right before write binlog cache to
  binary log.
 
  @param param The parameter for transaction observers
 
  @retval 0 Success
  @retval 1 Failure
*/
typedef int (*before_commit_t)(Trans_param *param);
 
/**
  This callback is called before transaction rollback
 
  This callback is called before rollback to storage engines.
 
  @param param The parameter for transaction observers
 
  @retval 0 Success
  @retval 1 Failure
*/
typedef int (*before_rollback_t)(Trans_param *param);
 
/**
  This callback is called after transaction commit
 
  This callback is called right after commit to storage engines for
  transactional tables.
 
  For non-transactional tables, this is called at the end of the
  statement, before sending statement status, if the statement
  succeeded.
 
  @note The return value is currently ignored by the server.
 
  @param param The parameter for transaction observers
 
  @retval 0 Success
  @retval 1 Failure
*/
typedef int (*after_commit_t)(Trans_param *param);
 
/**
  This callback is called after transaction rollback
 
  This callback is called right after rollback to storage engines
  for transactional tables.
 
  For non-transactional tables, this is called at the end of the
  statement, before sending statement status, if the statement
  failed.
 
  @note The return value is currently ignored by the server.
 
  @param param The parameter for transaction observers
 
  @retval 0 Success
  @retval 1 Failure
*/
typedef int (*after_rollback_t)(Trans_param *param);
 
/**
  This callback is called before a sql command is executed.
 
  @param param   The parameter for transaction observers
  @param out_val Return value from observer execution
 
  @retval 0 Success
  @retval 1 Failure
*/
typedef int (*begin_t)(Trans_param *param, int &out_val);
 
/**
   Observes and extends transaction execution
*/
typedef struct Trans_observer {
  uint32 len;
 
  before_dml_t before_dml;
  before_commit_t before_commit;
  before_rollback_t before_rollback;
  after_commit_t after_commit;
  after_rollback_t after_rollback;
  begin_t begin;
} Trans_observer;
 
/**
   Binlog storage flags
*/
enum Binlog_storage_flags {
  /** Binary log was sync:ed */
  BINLOG_STORAGE_IS_SYNCED = 1
};
 
typedef struct Server_state_param {
  uint32 server_id;
} Server_state_param;
 
/**
  This is called just before the server is ready to accept the client
  connections to the Server/Node. It marks the possible point where the
  server can be said to be ready to serve client queries.
 
  @param[in]  param Observer common parameter
 
  @retval 0 Success
  @retval >0 Failure
*/
typedef int (*before_handle_connection_t)(Server_state_param *param);
 
/**
  This callback is called before the start of the recovery
 
  @param[in]  param Observer common parameter
 
  @retval 0 Success
  @retval >0 Failure
*/
typedef int (*before_recovery_t)(Server_state_param *param);
 
/**
  This callback is called after the end of the engine recovery.
 
  This is called before the start of the recovery procedure ie.
  the engine recovery.
 
  @param[in]  param Observer common parameter
 
  @retval 0 Success
  @retval >0 Failure
*/
typedef int (*after_engine_recovery_t)(Server_state_param *param);
 
/**
  This callback is called after the end of the recovery procedure.
 
  @param[in]  param Observer common parameter
 
  @retval 0 Success
  @retval >0 Failure
*/
typedef int (*after_recovery_t)(Server_state_param *param);
 
/**
  This callback is called before the start of the shutdown procedure.
  Can be useful to initiate some cleanup operations in some cases.
 
  @param[in]  param Observer common parameter
 
  @retval 0 Success
  @retval >0 Failure
*/
typedef int (*before_server_shutdown_t)(Server_state_param *param);
 
/**
  This callback is called after the end of the shutdown procedure.
  Can be used as a checkpoint of the proper cleanup operations in some cases.
 
  @param[in]  param Observer common parameter
 
  @retval 0 Success
  @retval >0 Failure
*/
typedef int (*after_server_shutdown_t)(Server_state_param *param);
 
/**
  This is called just after an upgrade from MySQL 5.7 populates the data
  dictionary for the first time.
 
  @param[in]  param Observer common parameter
 
  @retval 0 Success
  @retval >0 Failure
*/
typedef int (*after_dd_upgrade_t)(Server_state_param *param);
 
/**
  Observer server state
 */
typedef struct Server_state_observer {
  uint32 len;
 
  before_handle_connection_t before_handle_connection;
  before_recovery_t before_recovery;
  after_engine_recovery_t after_engine_recovery;
  after_recovery_t after_recovery;
  before_server_shutdown_t before_server_shutdown;
  after_server_shutdown_t after_server_shutdown;
  after_dd_upgrade_t after_dd_upgrade_from_57;
} Server_state_observer;
 
/**
   Binlog storage observer parameters
 */
typedef struct Binlog_storage_param {
  uint32 server_id;
} Binlog_storage_param;
 
/**
  This callback is called after binlog has been flushed
 
  This callback is called after cached events have been flushed to
  binary log file but not yet synced.
 
  @param param Observer common parameter
  @param log_file Binlog file name been updated
  @param log_pos Binlog position after update
 
  @retval 0 Success
  @retval 1 Failure
*/
typedef int (*after_flush_t)(Binlog_storage_param *param, const char *log_file,
                             my_off_t log_pos);
typedef int (*after_sync_t)(Binlog_storage_param *param, const char *log_file,
                            my_off_t log_pos);
 
/**
   Observe binlog logging storage
*/
typedef struct Binlog_storage_observer {
  uint32 len;
 
  after_flush_t after_flush;
  after_sync_t after_sync;
} Binlog_storage_observer;
 
/**
   Replication binlog transmitter (binlog dump) observer parameter.
*/
typedef struct Binlog_transmit_param {
  uint32 server_id;
  uint32 flags;
  /* Let us keep 1-16 as output flags and 17-32 as input flags */
  static const uint32 F_OBSERVE = 1;
  static const uint32 F_DONT_OBSERVE = 2;
 
  void set_observe_flag() { flags |= F_OBSERVE; }
  void set_dont_observe_flag() { flags |= F_DONT_OBSERVE; }
  /**
     If F_OBSERVE is set by any plugin, then it should observe binlog
     transmission, even F_DONT_OBSERVE is set by some plugins.
 
     If both F_OBSERVE and F_DONT_OBSERVE are not set, then it is an old
     plugin. In this case, it should always observe binlog transmission.
   */
  bool should_observe() {
    return (flags & F_OBSERVE) || !(flags & F_DONT_OBSERVE);
  }
} Binlog_transmit_param;
 
/**
  This callback is called when binlog dumping starts
 
  @param param Observer common parameter
  @param log_file Binlog file name to transmit from
  @param log_pos Binlog position to transmit from
 
  @retval 0 Success
  @retval 1 Failure
*/
typedef int (*transmit_start_t)(Binlog_transmit_param *param,
                                const char *log_file, my_off_t log_pos);
 
/**
  This callback is called when binlog dumping stops
 
  @param param Observer common parameter
 
  @retval 0 Success
  @retval 1 Failure
*/
typedef int (*transmit_stop_t)(Binlog_transmit_param *param);
 
/**
  This callback is called to reserve bytes in packet header for event
  transmission
 
  This callback is called when resetting transmit packet header to
  reserve bytes for this observer in packet header.
 
  The @a header buffer is allocated by the server code, and @a size
  is the size of the header buffer. Each observer can only reserve
  a maximum size of @a size in the header.
 
  @param param Observer common parameter
  @param header Pointer of the header buffer
  @param size Size of the header buffer
  @param len Header length reserved by this observer
 
  @retval 0 Success
  @retval 1 Failure
*/
typedef int (*reserve_header_t)(Binlog_transmit_param *param,
                                unsigned char *header, unsigned long size,
                                unsigned long *len);
 
/**
  This callback is called before sending an event packet to slave
 
  @param param Observer common parameter
  @param packet Binlog event packet to send
  @param len Length of the event packet
  @param log_file Binlog file name of the event packet to send
  @param log_pos Binlog position of the event packet to send
 
  @retval 0 Success
  @retval 1 Failure
*/
typedef int (*before_send_event_t)(Binlog_transmit_param *param,
                                   unsigned char *packet, unsigned long len,
                                   const char *log_file, my_off_t log_pos);
 
/**
  This callback is called after an event packet is sent to the
  slave or is skipped.
 
  @param param             Observer common parameter
  @param event_buf         Binlog event packet buffer sent
  @param len               length of the event packet buffer
  @param skipped_log_file  Binlog file name of the event that
                           was skipped in the master. This is
                           null if the position was not skipped
  @param skipped_log_pos   Binlog position of the event that
                           was skipped in the master. 0 if not
                           skipped
  @retval 0 Success
  @retval 1 Failure
*/
typedef int (*after_send_event_t)(Binlog_transmit_param *param,
                                  const char *event_buf, unsigned long len,
                                  const char *skipped_log_file,
                                  my_off_t skipped_log_pos);
 
/**
  This callback is called after resetting master status
 
  This is called when executing the command RESET MASTER, and is
  used to reset status variables added by observers.
 
  @param param Observer common parameter
 
  @retval 0 Success
  @retval 1 Failure
*/
typedef int (*after_reset_master_t)(Binlog_transmit_param *param);
 
/**
   Observe and extends the binlog dumping thread.
*/
typedef struct Binlog_transmit_observer {
  uint32 len;
 
  transmit_start_t transmit_start;
  transmit_stop_t transmit_stop;
  reserve_header_t reserve_header;
  before_send_event_t before_send_event;
  after_send_event_t after_send_event;
  after_reset_master_t after_reset_master;
} Binlog_transmit_observer;
 
/**
   Binlog relay IO flags
*/
enum Binlog_relay_IO_flags {
  /** Binary relay log was sync:ed */
  BINLOG_RELAY_IS_SYNCED = 1
};
 
/**
  Replication binlog relay IO observer parameter
*/
typedef struct Binlog_relay_IO_param {
  uint32 server_id;
  my_thread_id thread_id;
 
  /* Channel name */
  char *channel_name;
 
  /* Master host, user and port */
  char *host;
  char *user;
  unsigned int port;
 
  char *master_log_name;
  my_off_t master_log_pos;
 
  MYSQL *mysql; /* the connection to master */
 
  bool source_connection_auto_failover;
} Binlog_relay_IO_param;
 
/**
  This callback is called when slave IO thread starts
 
  @param param Observer common parameter
 
  @retval 0 Success
  @retval 1 Failure
*/
typedef int (*thread_start_t)(Binlog_relay_IO_param *param);
 
/**
  This callback is called when slave IO thread stops
 
  @param param Observer common parameter
 
  @retval 0 Success
  @retval 1 Failure
*/
typedef int (*thread_stop_t)(Binlog_relay_IO_param *param);
 
/**
  This callback is called when a relay log consumer thread starts
 
  @param param Observer common parameter
 
  @retval 0 Success
  @retval 1 Failure
*/
typedef int (*applier_start_t)(Binlog_relay_IO_param *param);
 
/**
  This callback is called when a relay log consumer thread stops
 
  @param param   Observer common parameter
  @param aborted thread aborted or exited on error
 
  @retval 0 Success
  @retval 1 Failure
*/
typedef int (*applier_stop_t)(Binlog_relay_IO_param *param, bool aborted);
 
/**
  This callback is called before slave requesting binlog transmission from
  master
 
  This is called before slave issuing BINLOG_DUMP command to master
  to request binlog.
 
  @param param Observer common parameter
  @param flags binlog dump flags
 
  @retval 0 Success
  @retval 1 Failure
*/
typedef int (*before_request_transmit_t)(Binlog_relay_IO_param *param,
                                         uint32 flags);
 
/**
  This callback is called after read an event packet from master
 
  @param param Observer common parameter
  @param packet The event packet read from master
  @param len Length of the event packet read from master
  @param event_buf The event packet return after process
  @param event_len The length of event packet return after process
 
  @retval 0 Success
  @retval 1 Failure
*/
typedef int (*after_read_event_t)(Binlog_relay_IO_param *param,
                                  const char *packet, unsigned long len,
                                  const char **event_buf,
                                  unsigned long *event_len);
 
/**
  This callback is called after written an event packet to relay log
 
  @param param Observer common parameter
  @param event_buf Event packet written to relay log
  @param event_len Length of the event packet written to relay log
  @param flags flags for relay log
 
  @retval 0 Success
  @retval 1 Failure
*/
typedef int (*after_queue_event_t)(Binlog_relay_IO_param *param,
                                   const char *event_buf,
                                   unsigned long event_len, uint32 flags);
 
/**
  This callback is called after reset slave relay log IO status
 
  @param param Observer common parameter
 
  @retval 0 Success
  @retval 1 Failure
*/
typedef int (*after_reset_slave_t)(Binlog_relay_IO_param *param);
 
/**
  This callback is called before event gets applied
 
  @param param  Observer common parameter
  @param trans_param The parameter for transaction observers
  @param out Return value from observer execution to help validate event
  according to observer requirement.
 
  @retval 0 Success
  @retval 1 Failure
*/
typedef int (*applier_log_event_t)(Binlog_relay_IO_param *param,
                                   Trans_param *trans_param, int &out);
 
/**
   Observes and extends the service of slave IO thread.
*/
typedef struct Binlog_relay_IO_observer {
  uint32 len;
 
  thread_start_t thread_start;
  thread_stop_t thread_stop;
  applier_start_t applier_start;
  applier_stop_t applier_stop;
  before_request_transmit_t before_request_transmit;
  after_read_event_t after_read_event;
  after_queue_event_t after_queue_event;
  after_reset_slave_t after_reset_slave;
  applier_log_event_t applier_log_event;
} Binlog_relay_IO_observer;
 
/**
   Register a transaction observer
 
   @param observer The transaction observer to register
   @param p pointer to the internal plugin structure
 
   @retval 0 Success
   @retval 1 Observer already exists
*/
int register_trans_observer(Trans_observer *observer, void *p);
 
/**
   Unregister a transaction observer
 
   @param observer The transaction observer to unregister
   @param p pointer to the internal plugin structure
 
   @retval 0 Success
   @retval 1 Observer not exists
*/
int unregister_trans_observer(Trans_observer *observer, void *p);
 
/**
   Register a binlog storage observer
 
   @param observer The binlog storage observer to register
   @param p pointer to the internal plugin structure
 
   @retval 0 Success
   @retval 1 Observer already exists
*/
int register_binlog_storage_observer(Binlog_storage_observer *observer,
                                     void *p);
 
/**
   Unregister a binlog storage observer
 
   @param observer The binlog storage observer to unregister
   @param p pointer to the internal plugin structure
 
   @retval 0 Success
   @retval 1 Observer not exists
*/
int unregister_binlog_storage_observer(Binlog_storage_observer *observer,
                                       void *p);
 
/**
   Register a binlog transmit observer
 
   @param observer The binlog transmit observer to register
   @param p pointer to the internal plugin structure
 
   @retval 0 Success
   @retval 1 Observer already exists
*/
int register_binlog_transmit_observer(Binlog_transmit_observer *observer,
                                      void *p);
 
/**
   Unregister a binlog transmit observer
 
   @param observer The binlog transmit observer to unregister
   @param p pointer to the internal plugin structure
 
   @retval 0 Success
   @retval 1 Observer not exists
*/
int unregister_binlog_transmit_observer(Binlog_transmit_observer *observer,
                                        void *p);
 
/**
   Register a server state observer
 
   @param observer The server state observer to register
   @param p pointer to the internal plugin structure
 
   @retval 0 Success
   @retval 1 Observer already exists
*/
int register_server_state_observer(Server_state_observer *observer, void *p);
 
/**
   Unregister a server state observer
 
   @param observer The server state observer to unregister
   @param p pointer to the internal plugin structure
 
   @retval 0 Success
   @retval 1 Observer not exists
*/
int unregister_server_state_observer(Server_state_observer *observer, void *p);
 
/**
   Register a binlog relay IO (slave IO thread) observer
 
   @param observer The binlog relay IO observer to register
   @param p pointer to the internal plugin structure
 
   @retval 0 Success
   @retval 1 Observer already exists
*/
int register_binlog_relay_io_observer(Binlog_relay_IO_observer *observer,
                                      void *p);
 
/**
   Unregister a binlog relay IO (slave IO thread) observer
 
   @param observer The binlog relay IO observer to unregister
   @param p pointer to the internal plugin structure
 
   @retval 0 Success
   @retval 1 Observer not exists
*/
int unregister_binlog_relay_io_observer(Binlog_relay_IO_observer *observer,
                                        void *p);
 
/**
   Set thread entering a condition
 
   This function should be called before putting a thread to wait for
   a condition. @p mutex should be held before calling this
   function. After being waken up, @c thd_exit_cond should be called.
 
   @param opaque_thd      The thread entering the condition, NULL means current
   thread
   @param cond     The condition the thread is going to wait for
   @param mutex    The mutex associated with the condition, this must be
                   held before call this function
   @param stage    The new process message for the thread
   @param old_stage The old process message for the thread
   @param src_function The caller source function name
   @param src_file The caller source file name
   @param src_line The caller source line number
*/
void thd_enter_cond(void *opaque_thd, mysql_cond_t *cond, mysql_mutex_t *mutex,
                    const PSI_stage_info *stage, PSI_stage_info *old_stage,
                    const char *src_function, const char *src_file,
                    int src_line);
 
#define THD_ENTER_COND(P1, P2, P3, P4, P5) \
  thd_enter_cond(P1, P2, P3, P4, P5, __func__, __FILE__, __LINE__)
 
/**
   Set thread leaving a condition
 
   This function should be called after a thread being waken up for a
   condition.
 
   @param opaque_thd      The thread entering the condition, NULL means current
   thread
   @param stage    The process message, usually this should be the old process
                   message before calling @c thd_enter_cond
   @param src_function The caller source function name
   @param src_file The caller source file name
   @param src_line The caller source line number
*/
void thd_exit_cond(void *opaque_thd, const PSI_stage_info *stage,
                   const char *src_function, const char *src_file,
                   int src_line);
 
#define THD_EXIT_COND(P1, P2) \
  thd_exit_cond(P1, P2, __func__, __FILE__, __LINE__)
 
/**
   Get the value of user variable as an integer.
 
   This function will return the value of variable @a name as an
   integer. If the original value of the variable is not an integer,
   the value will be converted into an integer.
 
   @param name     user variable name
   @param value    pointer to return the value
   @param null_value if not NULL, the function will set it to true if
   the value of variable is null, set to false if not
 
   @retval 0 Success
   @retval 1 Variable not found
*/
int get_user_var_int(const char *name, long long int *value, int *null_value);
 
/**
   Get the value of user variable as a double precision float number.
 
   This function will return the value of variable @a name as real
   number. If the original value of the variable is not a real number,
   the value will be converted into a real number.
 
   @param name     user variable name
   @param value    pointer to return the value
   @param null_value if not NULL, the function will set it to true if
   the value of variable is null, set to false if not
 
   @retval 0 Success
   @retval 1 Variable not found
*/
int get_user_var_real(const char *name, double *value, int *null_value);
 
/**
   Get the value of user variable as a string.
 
   This function will return the value of variable @a name as
   string. If the original value of the variable is not a string,
   the value will be converted into a string.
 
   @param name     user variable name
   @param value    pointer to the value buffer
   @param len      length of the value buffer
   @param precision precision of the value if it is a float number
   @param null_value if not NULL, the function will set it to true if
   the value of variable is null, set to false if not
 
   @retval 0 Success
   @retval 1 Variable not found
*/
int get_user_var_str(const char *name, char *value, size_t len,
                     unsigned int precision, int *null_value);
 
#ifdef __cplusplus
}
#endif
#endif /* REPLICATION_H */