Bug #96072 MySQLDump appears to be missing an option to specify "FOR CHANNEL"
Submitted: 2 Jul 2019 11:12 Modified: 2 Jul 2019 13:05
Reporter: IGG t Email Updates:
Status: Verified Impact on me:
Category:MySQL Server: mysqldump Command-line Client Severity:S4 (Feature request)
Version: OS:Any
Assigned to: CPU Architecture:Any
Tags: mysqldump

[2 Jul 2019 11:12] IGG t
When trying to set up multi-source replication, it became apparent that mysqldump doesn't have an option to specify the channel to use, thus making it very difficult to set up.

If you look at the output for MySQL dump it contains a CHANGE MASTER STATEMENT, but there doesn't appear to be a way to make mysqldump include a CHANGE MASTER ... FOR CHANNEL 'channelName'

The only workarounds require twice as much disk space and twice the amount of time, so you can save it as a file, then manually edit the file before importing it, or importing one, then breaking replication, importing the second one, then starting replication on both. Neither of which is a particularly good solution.

How to repeat:
Set up two separate databases. 

DB1 with the schema test1
DB2 with the schema test2

Set up a third database, DB3, to use as the multi-source SLAVE for DB1 and DB2 masters.

Run mysqldump on DB3 to get the test1 schema from DB1

mysqldump -h1.2.3.4 -P3306 -umysqldumpuser -ppassword --dump-slave --apply-slave-statements --include-master-host-port --single-transaction --databases test1 -E -R -q -c --max_allowed_packet=2G | mysql -S/var/run/mysqld/mysqld.sock -umysqldumpuser -ppassword

You now have test1 on DB3, replicating from DB1. However, it is using the "" channel, so you need to change this manually.


. . .     
FOR CHANNEL '<channel_name>;

If I now try and load test2 from DB2:

mysqldump -h1.2.3.5 -P3306 -umysqldumpuser -ppassword --dump-slave --apply-slave-statements --include-master-host-port --single-transaction --databases test2 -E -R -q -c --max_allowed_packet=2G | mysql -S/var/run/mysqld/mysqld.sock -umysqldumpuser -ppassword

I get an error:

"ERROR 3079 (HY000) at line 28: Multiple channels exist on the slave. Please provide channel name as an argument."

But there is (as far as I can tell) no option to specify the channel name to use.

Suggested fix:
Add an option to mysqldump so you can specify the channel name to use. Then this could be appended to the `CHANGE MASTER` statement inside the mysqldump output.
[2 Jul 2019 13:05] MySQL Verification Team
Hi Mr. IGG,

Thank you for your bug report.

I have analysed it and I consider it a welcome feature request.

Verified as a feature request.
[2 Jul 2019 13:06] MySQL Verification Team
This feature will of course require one more option in mysqldump.