relay's behaviour should align with MySQL when using GTID

[lance6716]

Bug Report

https://dev.mysql.com/doc/refman/5.7/en/replication-gtids-auto-positioning.html

The source responds by sending all transactions recorded in its binary log whose GTID is not included in the GTID set sent by the replica. To do this, the source first identifies the appropriate binary log file to begin working with, by checking the Previous_gtids_log_event in the header of each of its binary log files, starting with the most recent. When the source finds the first Previous_gtids_log_event which contains no transactions that the replica is missing, it begins with that binary log file. This method is efficient and only takes a significant amount of time if the replica is behind the source by a large number of binary log files. The source then reads the transactions in that binary log file and subsequent files up to the current one, sending the transactions with GTIDs that the replica is missing, and skipping the transactions that were in the GTID set sent by the replica. The elapsed time until the replica receives the first missing transaction depends on its offset in the binary log file. This exchange ensures that the source only sends the transactions with a GTID that the replica has not already received or committed. If the replica receives transactions from more than one source, as in the case of a diamond topology, the auto-skip function ensures that the transactions are not applied twice.

1. getPosByGTID may choose start position by

   choose a relay log file that its "Previous_gtids_log_event" don't overlap with "complementary set of given GTID set", which could reduce to "Previous_gtids_log_event" is subset or equal to "given GTID set"

2. scan the relay log and skip the transactions in "given GTID set", to handle cases when given GTID set is not continuous like uuid:1-10:20-30

[lance6716]

when MySQL use GTID replication and slave didn't enable binlog, user can't use slave as upstream of DM because DM is based on binlog replication. Assuming at that time the GTID set is

xxx:1-10

User enables binlog on slave then, the first binlog of slave will have an empty Previous_gtids, and next binlog files will have Previous_gtids starting from 11. Meanwhile select * from mysql.gtid_executed or select @@global.gtid_executed will output GTID set starting from 1, select @@global.gtid_purged will output xxx:1-10

[GMHDBJD]

Did you use MASTER_AUTO_POSITION = 1 ?

[lance6716]

Did you use MASTER_AUTO_POSITION = 1 ?

didn't use it when CHANGE MASTER

[GMHDBJD]

What's the output of show master status ? Does the output start from 1?

[lance6716]

What's the output of show master status ?

starting from 1. accroding to MySQL doc, show master status will output gtid_executed