Hi Guillaume,

Thank you for that. The only options I have in the config file is:
router_options=max_sescmd_history=4096
That's all.

I can add it but that would require maxscale to restart would it not ?

If I set wsrep_desync=1 on one of the nodes... how do I know that node will be marked as a donor ?

At the moment I have this in Galera config:
wsrep_cluster_address="gcomm://10.44.167.11,10.44.167.12,10.44.167.13,10.44.167.19,10.44.167.20"

So I need to expand that list by the 2 other servers is that correct ?
That also requires a mysql restart on each node in the cluster ?

I'm just a bit worried about those restarts as we had situations in the past when the nodes got stuck on "joining" without actually transferring anything but I think we have actually fixed it now.

Thank you.

Regards,
TH

On 4 July 2016 at 10:29, Guillaume Lefranc <guillaume.lefranc@mariadb.com> wrote:
Hi,

SET GLOBAL wsrep_desync=1 will set a node as desynced and will cause MaxScale to stop sending traffic to it (provided you use router_options=synced in your maxscale.cnf config file)

-GL

On Mon, Jul 4, 2016 at 11:25 AM Thorvald Hallvardsson <thorvald.hallvardsson@gmail.com> wrote:
Hi guys,

I need some help as I'm preparing to expand my existing Galera cluster. Generally the purpose of it is I need to replace 3 VMs I have a cluster running on to 2 physical servers I have been given for that purpose.

My idea was to join 2 physical cluster to the existing cluster of 3 and then remove all 3 VMs from the cluster leaving 2 physical nodes within. I have a arbitrator box within the cluster as well.

The config at the moment contains 2 maxscale proxy nodes on the front balancing the read queries across the entire cluster of 3 and write queries to the elected master.

What I want to achieve is as I said above but + I will need another help with maxscale to expand and then shrink the cluster down to 2 nodes afterwards. I have had a situation before when I had to do a simple config change on the Galera cluster and I was trying to mark nodes and put them into maintenance mode to stop traffic coming to them but the commands like set server NODE master didn't actually do anything. I had situations when I had 2 masters in the cluster for a second because then something was happening that my manually selected master was becoming a slave again. I couldn't find anything on the internet what would point me into right direction and explain the whole procedure in details.

My cluster is quite busy at the moment even overnight so there is no perfect time to do anything on it. I need to do it the least disruptive way and the most controlled way as well. Hence I'm asking for help and suggestions as I found both Galera and maxscale documentation very very brief not actually providing any decent details or procedures. I found much more help from Percona but descriptions don't match sometimes.

Please help.

Regards,
TH
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Guillaume Lefranc
Remote DBA Services Manager
MariaDB Corporation