MDEV-4984: Implement MASTER_GTID_WAIT() and @@LAST_GTID.

MASTER_GTID_WAIT() is similar to MASTER_POS_WAIT(), but works with a
GTID position rather than an old-style filename/offset.

@@LAST_GTID gives the GTID assigned to the last transaction written
into the binlog.

Together, the two can be used by applications to obtain the GTID of
an update on the master, and then do a MASTER_GTID_WAIT() for that
position on any read slave where it is important to get results that
are caught up with the master at least to the point of the update.

The implementation of MASTER_GTID_WAIT() is implemented in a way
that tries to minimise the performance impact on the SQL threads,
even in the presense of many waiters on single GTID positions (as
from @@LAST_GTID).

1 files changed, 2 insertions, 0 deletions

diff --git a/sql/sql_repl.h b/sql/sql_repl.h
index da55e3e863f..defb1b23f5b 100644
--- a/sql/sql_repl.h
+++ b/sql/sql_repl.h
@@ -70,6 +70,8 @@ void mysql_binlog_send(THD* thd, char* log_ident, my_off_t pos, ushort flags);
 extern PSI_mutex_key key_LOCK_slave_state, key_LOCK_binlog_state;
 void rpl_init_gtid_slave_state();
 void rpl_deinit_gtid_slave_state();
+void rpl_init_gtid_waiting();
+void rpl_deinit_gtid_waiting();
 int gtid_state_from_binlog_pos(const char *name, uint32 pos, String *out_str);
 int rpl_append_gtid_state(String *dest, bool use_binlog);
 int rpl_load_gtid_state(slave_connection_state *state, bool use_binlog);