Setting up multi-source replication (MySQL 8.0) with GTID based replication

Last week I posted a blog on how to setup multi-source for MySQL 5.7 using GTID based replication, in this blog we will do the same using MySQL 8.0.

Most of the procedure are the same, there are only two things that we need to change are;
1) Procedure for creating the replication user.
2) Fetching the GTID value from the MySQL dumpfile.

1) Create replication user for MySQL 8
MySQL 8 uses a new authentication plugin so to create the replication user will differ from MySQL 5.7. The procedure for 5.7 was with:

mysql> CREATE USER 'repl_user'@'slave-host' IDENTIFIED BY 'repl_pass';
mysql> GRANT REPLICATION SLAVE ON *.* TO 'repl_user'@'slave-host';

With MySQL 8 you need to create the user like:

mysql> CREATE USER 'repl_user'@'slave-host' IDENTIFIED WITH sha256_password BY 'repl_pass';
mysql> GRANT REPLICATION SLAVE ON *.* TO 'repl_user'@'slave-host';

Another option is to configure MySQL to use old authentication method, then you do not have to modify the CREATE statement above. This can be done by setting configuration variable default_authentication_plugin to "mysql_native_password".

2) Changed format of GTID_PURGED information in dumpfile
The GTID_PURGED information in the dumpfile now include a comment like:

SET @@GLOBAL.GTID_PURGED=/*!80000 '+'*/ 'dfa44283-d466-11e9-80ec-ec21e522bf21:1-6';

To fetch the GTID you now have to use below command that will remove also the new comment:

cat dumpM1.sql | grep GTID_PURGED | perl -p0 -e 's#/\*.*?\*/##sg' | cut -f2 -d'=' | cut -f2 -d$'\''

The github page and the scripts to create a test environment have also been updated!

Setting up multi-source replication (5.7) with GTID based replication

Purpose of this guide is to show how to setup a new multi-source slave from two (or more) existing masters. We will also set up a replication filter to only apply data from some of the databases.

So the scenarios is that we have already 2 master up and running and we want filter one database from each. Lets call them master1 and master2 with databases master1 and master2 to make it easy.

First step will be to make sure that both the master databases have GTID replication enabled. Configuration (my.cnf) needed on master servers will be (restart of databases will be needed):

gtid-mode=ON log-slave-updates=ON enforce-gtid-consistency=true master-info-repository=TABLE relay-log-info-repository=TABLE log-bin=mysql-bin binlog-format=ROW

Next step is to create a user for replication on both master servers:

mysql> CREATE USER 'repl_user'@'slave-host' IDENTIFIED BY 'repl_pass'; mysql> GRANT REPLICATION SLAVE ON *.* TO 'repl_user'@'slave-host';

Provisioning of data to new multi-source slave

1) Now it's time to provision some data to our slave, step one is to run mysqldump on master databases: 

mysqldump -u<user> -p<pass> --single-transaction --triggers --routines --set-gtid-purged=ON --databases master1 > dumpM1.sql mysqldump -u<user> -p<pass> --single-transaction --triggers --routines --set-gtid-purged=ON --databases master2 > dumpM2.sql

(we only dump database master1 from master1 and master2 from master2)

2) Get GTID_PURGED information from dump files and remember this (you need this later):

cat dumpM1.sql | grep GTID_PURGED | cut -f2 -d'=' | cut -f2 -d$'\'' cat dumpM2.sql | grep GTID_PURGED | cut -f2 -d'=' | cut -f2 -d$'\''

(should look something like: aeaeb1f9-cfab-11e9-bf5d-ec21e522bf21:1-5)

3) Now we need to remove GTID_PURGED information from dump files before import:

sed '/GTID_PURGED/d' dumpM1.sql > dumpM1_nopurge.sql sed '/GTID_PURGED/d' dumpM2.sql > dumpM2_nopurge.sql

4) Import data into new multi-source slave:

mysql -u<user> -p<pass> < dumpM1_nopurge.sql mysql -u<user> -p<pass> < dumpM2_nopurge.sql

5) Clear GTID state of slave server and set GTID_PURGED to values collected earlier in step 2):

mysql> RESET MASTER; mysql> SET GLOBAL GTID_PURGED="<Master1 GTID_PURGED>,<Master2 GTID_PURGED>";

Configure and start multi-source replication

1) Now it's time to configure the replication channels and set the filter rule
    (filters on slave will be for all channels):

mysql> CHANGE MASTER TO MASTER_HOST=<master1-host>, MASTER_USER="repl", MASTER_PASSWORD="repl", MASTER_AUTO_POSITION=1 FOR CHANNEL "master1"; mysql> CHANGE MASTER TO MASTER_HOST=<master2-host>, MASTER_USER="repl", MASTER_PASSWORD="repl", MASTER_AUTO_POSITION=1 FOR CHANNEL "master2"; mysql> CHANGE REPLICATION FILTER REPLICATE_WILD_DO_TABLE=('master1.%','master2.%');

2) After this we start both channels:

mysql> START SLAVE FOR CHANNEL "master1"; mysql> START SLAVE FOR CHANNEL "master2";

3) You can now looks at status with:

mysql> SHOW SLAVE STATUS FOR CHANNEL "master1"\G mysql> SHOW SLAVE STATUS FOR CHANNEL "master2"\G

Setup your own multi-source sandbox environment

If you want to play around with Multi-Source replication and want to jumpstart a sandbox environment then you might want to look at my workshop at GitHub.