Comments - Getting Started with MariaDB Galera Cluster

I've faced a problem building a cluster with docker. A new container cant join a cluster in its first start. i'ts needed to start first the container with wsrep_on=off (or unset), let mariadb initialize internal db (or whatever). And then restart with wsrep_on and join the cluster. I've been struggling with it for days so, at least a comment here.

I have two questions: 1. Can a cluster have a non-member replication master te replicate data from (like multi-master) 2. Can a cluster replicate to a non-member?

Hi, Is possible to specify only one database instead of all databases of the server? I did not find information about it.

Thank you.

Hi, I have a question around auto_increment values - is it always guaranteed to be in the ascending order? To give an example, say we have a 2 node cluster with the following settings

Node1: @@auto_increment_increment=2, @@auto_increment_offset=1 Node2: @@auto_increment_increment=2, @@auto_increment_offset=2

If 2 rows are inserted from Node1 into a table with an auto_increment primary key the IDs generated will be 1 and 3. If the next insert into the table is from Node2 the ID should be 4 as opposed to 2.

Thanks Raghav

Yes.

There is rarely a good reason not to have 3 nodes. With two you don't have a automated failure recovery

The autoincrement is sorted with the wsrep_auto_increment_control=1 (the default)

If the insert on Node 2 occurs before the from Node 1 applies you may get 2.

autoincrements can have gaps (due to transaction rollback). Use last_insert_id if you want the value of a last insert. Don't try to predict them.

Thanks Daniel, I used the two node example just to keep it simple.What happens if there are simultaneous inserts in more than one node for a particular table is that arbitrated somehow by the cluster and Ids generated accordingly?

Thanks

Raghav

Does xtrabackup method work with RPMs? The script complains that innobackupex is not available:
$ /usr/bin/wsrep_sst_xtrabackup
Can't find innobackupex in the path
I've been searching for innobackupex inside all RPMs but I found nothing.
Is this script available on some other package? Can it be downloaded separately?

p.s.: rsync works properly, but I don't like the fact that it blocks the database during the transfer.

innobackupex is available from Percona http://www.percona.com/software/percona-xtrabackup

Along with aRoboto comment about wsrep_sst_auth user needing to have full root access to all databases. Is it consider safe to have a root username and password in plain text in a world-readable file? It seems like something I would want to avoid. Does anyone have an suggestions for this or am I am just being paranoid?

You don't really need "full access". If you search around you'll see what permissions you need on the databases. First of all you create a specific user for SST transfers, than you give permission 640 to your /etc/my.cnf.d/server.cnf file, and assign it to mysql:mysql. At the end if you liked this explanaton, you can configure your cluster by using my tool: https://github.com/maxadamo/galera-wizard

p.s.: of course you can also implemente SSL for your replication....

Cheers.

Just a suggestion, but the wsrep_sst_auth variable may need to be explained more clearly. I stumbled on this for a few hours. The only reason I figured this out was by looking at the mysql error log on the DONOR.

The errors looked like this:

[ERROR] WSREP: Process completed with error: wsrep_sst_mysqldump --user '' --password '' --host '172.20.1.123' --port '3306' --local-port '33 06' --socket '/var/lib/mysql/mysql.sock' --gtid '5a568cb8-c658-11e2-0800-29e7f95d4235:0': 2 (No such file or directory)

wsrep_sst_auth needs to be defined with a username and password with root access to all dbservers in either my.cnf or as an argument to your mysqld command. The format for my.cnf is:

wsrep_sst_auth=username:password

Hope this helps.