[#MDEV-4688] gtid_current_pos and gtid_slave_pos have empty values most of the time when slave is replicating

I'm not sure if it's a bug, maybe it's supposed to work this way, but it surely looks strange, so I'll file it and leave it to you to decide

When a slave is actively replicating, most of the time @@gtid_current_pos and @@gtid_slave_pos appear to be empty. No special flow seems to be necessary, just regular DML would suffice. For example, the test below performs a thousand of inserts on master while checking the values on the slave at the same time. Here is a typical extract from the output:

Variable_name   Value

gtid_binlog_pos 0-1-513

gtid_current_pos

gtid_slave_pos

Variable_name   Value

gtid_binlog_pos 0-1-523

gtid_current_pos

gtid_slave_pos

Variable_name   Value

gtid_binlog_pos 0-1-530

gtid_current_pos        0-1-530

gtid_slave_pos  0-1-530

Variable_name   Value

gtid_binlog_pos 0-1-540

gtid_current_pos

gtid_slave_pos

Variable_name   Value

gtid_binlog_pos 0-1-548

gtid_current_pos

gtid_slave_pos

Variable_name   Value

gtid_binlog_pos 0-1-559

gtid_current_pos

gtid_slave_pos

If instead of a number of small statements I execute one very big statement, the effect can still be observed, but the empty values only appear during a small fraction of time. So, I presume the "empty phase" has somewhat flat duration per an event group, regardless its size.

Test case:

--source include/master-slave.inc

--source include/have_innodb.inc

--source include/have_binlog_format_row.inc

--connection slave

--source include/stop_slave.inc

change master to master_use_gtid=current_pos;

--source include/start_slave.inc

--connection master

create table t1 (i int, c varchar(8)) engine=InnoDB;

--delimiter |

create procedure p(n int)

begin

	while n > 0 do

		insert into t1 values (1,'test1'),(2,'test2'),(3,'test3'),(4,'test4');

		set n = n - 1;

	end while;

end|

--delimiter ;

send call p(1000);

--connection slave

let $run = 100;

--disable_query_log

while ($run)

	SHOW VARIABLES LIKE 'gtid%pos';

	--sleep 1

	dec $run;

--connection master

--reap

drop table t1;

drop procedure p;

--sync_slave_with_master

--connection master

--source include/rpl_end.inc

bzr version-info

revision-id: sergii@pisem.net-20130610064025-makoe3xkewwwky8j

revno: 3761

branch-nick: 10.0

[MDEV-4688] gtid_current_pos and gtid_slave_pos have empty values most of the time when slave is replicating Created: 2013-06-20 Updated: 2013-06-21 Resolved: 2013-06-21
Status:	Closed
Project:	MariaDB Server
Component/s:	None
Affects Version/s:	None
Fix Version/s:	10.0.5

[MDEV-4688] gtid_current_pos and gtid_slave_pos have empty values most of the time when slave is replicating Created: 2013-06-20 Updated: 2013-06-21 Resolved: 2013-06-21