MDEV-26: Global transaction ID.

When starting slave, check binlog state in addition to mysql.rpl_slave.state.

This allows to switch a previous master to be a slave directly
with MASTER_GTID_POS=AUTO.

sql/log.cc

@@ -120,7 +120,7 @@ static MYSQL_BIN_LOG::xid_count_per_binlog *
 static bool start_binlog_background_thread();
 
 
-rpl_binlog_state rpl_global_gtid_binlog_state;
+static rpl_binlog_state rpl_global_gtid_binlog_state;
 
 /**
    purge logs, master and slave sides both, related error code
@@ -5488,6 +5488,13 @@ end:
 }
 
 
+int
+MYSQL_BIN_LOG::get_most_recent_gtid_list(rpl_gtid **list, uint32 *size)
+{
+  return rpl_global_gtid_binlog_state.get_most_recent_gtid_list(list, size);
+}
+
+
 /**
   Write an event to the binary log. If with_annotate != NULL and
   *with_annotate = TRUE write also Annotate_rows before the event
@@ -8176,8 +8183,7 @@ int TC_LOG_BINLOG::open(const char *opt_name)
     else
       error= read_state_from_file();
     /* Pick the next unused seq_no from the loaded/recovered binlog state. */
-    global_gtid_counter= rpl_global_gtid_binlog_state.seq_no_for_server_id
-      (global_system_variables.server_id);
+    global_gtid_counter= rpl_global_gtid_binlog_state.seq_no_from_state();
 
     delete ev;
     end_io_cache(&log);

sql/log.h

@@ -396,6 +396,7 @@ private:
   ( ((ulong)(c)>>1) == BINLOG_COOKIE_DUMMY_ID )
 
 class binlog_cache_mngr;
+class rpl_gtid;
 class MYSQL_BIN_LOG: public TC_LOG, private MYSQL_LOG
 {
  private:
@@ -773,6 +774,7 @@ public:
   bool write_gtid_event(THD *thd, bool standalone, bool is_transactional);
   int read_state_from_file();
   int write_state_to_file();
+  int get_most_recent_gtid_list(rpl_gtid **list, uint32 *size);
 };
 
 class Log_event_handler

sql/log_event.h

@@ -2981,7 +2981,7 @@ struct rpl_slave_state
     uint32 domain_id;
 
     list_element *grab_list() { list_element *l= list; list= NULL; return l; }
-    void add (list_element *l)
+    void add(list_element *l)
     {
       l->next= list;
       list= l;
@@ -3008,7 +3008,7 @@ struct rpl_slave_state
   int record_gtid(THD *thd, const rpl_gtid *gtid, uint64 sub_id,
                       bool in_transaction);
   uint64 next_subid(uint32 domain_id);
-  int tostring(String *dest);
+  int tostring(String *dest, rpl_gtid *extra_gtids, uint32 num_extra);
   bool is_empty();
 
   void lock() { DBUG_ASSERT(inited); mysql_mutex_lock(&LOCK_slave_state); }
@@ -3027,10 +3027,21 @@ struct rpl_slave_state
   containing a gigen GTID, by simply scanning backwards from the newest
   one until a lower seq_no is found in the Gtid_list_log_event at the
   start of a binlog for the given domain_id and server_id.
+
+  We also remember the last logged GTID for every domain_id. This is used
+  to know where to start when a master is changed to a slave. As a side
+  effect, it also allows to skip a hash lookup in the very common case of
+  logging a new GTID with same server id as last GTID.
 */
 struct rpl_binlog_state
 {
-  /* Mapping from (domain_id,server_id) to its GTID. */
+  struct element {
+    uint32 domain_id;
+    HASH hash;                /* Containing all server_id for one domain_id */
+    /* The most recent entry in the hash. */
+    rpl_gtid *last_gtid;
+  };
+  /* Mapping from domain_id to collection of elements. */
   HASH hash;
   /* Mutex protecting access to the state. */
   mysql_mutex_t LOCK_binlog_state;
@@ -3038,12 +3049,14 @@ struct rpl_binlog_state
   rpl_binlog_state();
   ~rpl_binlog_state();
 
-  ulong count() const { return hash.records; }
-  int update(const struct rpl_gtid *gtid);
   void reset();
-  uint32 seq_no_for_server_id(uint32 server_id);
+  int update(const struct rpl_gtid *gtid);
+  uint32 seq_no_from_state();
   int write_to_iocache(IO_CACHE *dest);
   int read_from_iocache(IO_CACHE *src);
+  uint32 count();
+  int get_gtid_list(rpl_gtid *gtid_list, uint32 list_size);
+  int get_most_recent_gtid_list(rpl_gtid **list, uint32 *size);
 };
 
 

sql/slave.cc

@@ -1792,10 +1792,29 @@ after_set_capability:
     char str_buf[256];
     String connect_state(str_buf, sizeof(str_buf), system_charset_info);
     connect_state.length(0);
+    rpl_gtid *binlog_gtid_list= NULL;
+    uint32 num_binlog_gtids= 0;
+
+    if (opt_bin_log)
+    {
+      int err= mysql_bin_log.get_most_recent_gtid_list(&binlog_gtid_list,
+                                                       &num_binlog_gtids);
+      if (err)
+      {
+        err_code= ER_OUTOFMEMORY;
+        errmsg= "The slave I/O thread stops because a fatal out-of-memory "
+          "error is encountered when it tries to compute @slave_connect_state.";
+        sprintf(err_buff, "%s Error: Out of memory", errmsg);
+        goto err;
+      }
+    }
 
     connect_state.append(STRING_WITH_LEN("SET @slave_connect_state='"),
                          system_charset_info);
-    rpl_global_gtid_slave_state.tostring(&connect_state);
+    rpl_global_gtid_slave_state.tostring(&connect_state, binlog_gtid_list,
+                                         num_binlog_gtids);
+    if (binlog_gtid_list)
+      my_free(binlog_gtid_list);
     connect_state.append(STRING_WITH_LEN("'"), system_charset_info);
     rc= mysql_real_query(mysql, connect_state.ptr(), connect_state.length());
     if (rc)