Fixed close_cached_connection_tables() flushing

Let DROP SERVER and ALTER SERVER perform fair affected tables flushing.
That is acquire MDL_EXCLUSIVE and do tdc_remove_table(TDC_RT_REMOVE_ALL).

Aim of this patch is elimination of another inconsistent use of
TDC_RT_REMOVE_UNUSED. It fixes (to some extent) a problem described in the
beginning of sql_server.cc, when close_cached_connection_tables()
interferes with concurrent transaction.

A better fix should probably introduce proper MDL locks for server
objects?

Part of MDEV-17882 - Cleanup refresh version

sql/sql_base.cc

@@ -630,93 +630,6 @@ bool flush_tables(THD *thd, flush_tables_type flag)
 }
 
 
-/**
-  Close all tables which match specified connection string or
-  if specified string is NULL, then any table with a connection string.
-*/
-
-struct close_cached_connection_tables_arg
-{
-  THD *thd;
-  LEX_CSTRING *connection;
-  TABLE_LIST *tables;
-};
-
-
-static my_bool close_cached_connection_tables_callback(
-  TDC_element *element, close_cached_connection_tables_arg *arg)
-{
-  TABLE_LIST *tmp;
-
-  mysql_mutex_lock(&element->LOCK_table_share);
-  /* Ignore if table is not open or does not have a connect_string */
-  if (!element->share || !element->share->connect_string.length ||
-      !element->ref_count)
-    goto end;
-
-  /* Compare the connection string */
-  if (arg->connection &&
-      (arg->connection->length > element->share->connect_string.length ||
-       (arg->connection->length < element->share->connect_string.length &&
-        (element->share->connect_string.str[arg->connection->length] != '/' &&
-         element->share->connect_string.str[arg->connection->length] != '\\')) ||
-       strncasecmp(arg->connection->str, element->share->connect_string.str,
-                   arg->connection->length)))
-    goto end;
-
-  /* close_cached_tables() only uses these elements */
-  if (!(tmp= (TABLE_LIST*) alloc_root(arg->thd->mem_root, sizeof(TABLE_LIST))) ||
-      !(arg->thd->make_lex_string(&tmp->db, element->share->db.str, element->share->db.length)) ||
-      !(arg->thd->make_lex_string(&tmp->table_name, element->share->table_name.str,
-                                      element->share->table_name.length)))
-  {
-    mysql_mutex_unlock(&element->LOCK_table_share);
-    return TRUE;
-  }
-
-  tmp->next_local= arg->tables;
-  arg->tables= tmp;
-
-end:
-  mysql_mutex_unlock(&element->LOCK_table_share);
-  return FALSE;
-}
-
-
-/**
-  Close cached connections
-
-  @return false  ok
-  @return true   If there was an error from closed_cached_connection_tables or
-                 if there was any open connections that we had to force closed
-*/
-
-bool close_cached_connection_tables(THD *thd, LEX_CSTRING *connection)
-{
-  bool res= false;
-  close_cached_connection_tables_arg argument;
-  DBUG_ENTER("close_cached_connections");
-  DBUG_ASSERT(thd);
-
-  argument.thd= thd;
-  argument.connection= connection;
-  argument.tables= NULL;
-
-  if (tdc_iterate(thd,
-                  (my_hash_walk_action) close_cached_connection_tables_callback,
-                  &argument))
-    DBUG_RETURN(true);
-
-  for (TABLE_LIST *table= argument.tables; table; table= table->next_local)
-    res|= tdc_remove_table(thd, TDC_RT_REMOVE_UNUSED,
-                           table->db.str,
-                           table->table_name.str);
-
-  /* Return true if we found any open connections */
-  DBUG_RETURN(res);
-}
-
-
 /*
   Mark all tables in the list which were used by current substatement
   as free for reuse.

sql/sql_base.h

@@ -306,7 +306,6 @@ bool close_cached_tables(THD *thd, TABLE_LIST *tables,
                          bool wait_for_refresh, ulong timeout);
 void purge_tables();
 bool flush_tables(THD *thd, flush_tables_type flag);
-bool close_cached_connection_tables(THD *thd, LEX_CSTRING *connect_string);
 void close_all_tables_for_name(THD *thd, TABLE_SHARE *share,
                                ha_extra_function extra,
                                TABLE *skip_table);

sql/sql_servers.cc

@@ -124,6 +124,79 @@ static void init_servers_cache_psi_keys(void)
 }
 #endif /* HAVE_PSI_INTERFACE */
 
+
+struct close_cached_connection_tables_arg
+{
+  THD *thd;
+  LEX_CSTRING *connection;
+  TABLE_LIST *tables;
+};
+
+
+static my_bool close_cached_connection_tables_callback(
+  TDC_element *element, close_cached_connection_tables_arg *arg)
+{
+  TABLE_LIST *tmp;
+
+  mysql_mutex_lock(&element->LOCK_table_share);
+  /* Ignore if table is not open or does not have a connect_string */
+  if (!element->share || !element->share->connect_string.length ||
+      !element->ref_count)
+    goto end;
+
+  /* Compare the connection string */
+  if (arg->connection &&
+      (arg->connection->length > element->share->connect_string.length ||
+       (arg->connection->length < element->share->connect_string.length &&
+        (element->share->connect_string.str[arg->connection->length] != '/' &&
+         element->share->connect_string.str[arg->connection->length] != '\\')) ||
+       strncasecmp(arg->connection->str, element->share->connect_string.str,
+                   arg->connection->length)))
+    goto end;
+
+  /* close_cached_tables() only uses these elements */
+  if (!(tmp= (TABLE_LIST*) alloc_root(arg->thd->mem_root, sizeof(TABLE_LIST))) ||
+      !(arg->thd->make_lex_string(&tmp->db, element->share->db.str, element->share->db.length)) ||
+      !(arg->thd->make_lex_string(&tmp->table_name, element->share->table_name.str,
+                                      element->share->table_name.length)))
+  {
+    mysql_mutex_unlock(&element->LOCK_table_share);
+    return TRUE;
+  }
+
+  tmp->next_local= arg->tables;
+  arg->tables= tmp;
+
+end:
+  mysql_mutex_unlock(&element->LOCK_table_share);
+  return FALSE;
+}
+
+
+/**
+  Close all tables which match specified connection string or
+  if specified string is NULL, then any table with a connection string.
+
+  @return false  ok
+  @return true   error, some tables may keep using old server info
+*/
+
+static bool close_cached_connection_tables(THD *thd, LEX_CSTRING *connection)
+{
+  close_cached_connection_tables_arg argument= { thd, connection, 0 };
+  DBUG_ENTER("close_cached_connections");
+
+  if (tdc_iterate(thd,
+                  (my_hash_walk_action) close_cached_connection_tables_callback,
+                  &argument))
+    DBUG_RETURN(true);
+
+  DBUG_RETURN(argument.tables ?
+              close_cached_tables(thd, argument.tables, true,
+                                  thd->variables.lock_wait_timeout) : false);
+}
+
+
 /*
   Initialize structures responsible for servers used in federated
   server scheme information for them from the server