wsrep variable to reject queries

[Raghavendra D Prabhu]

Similar to wsrep_sst_donor_rejects_queries, it would be useful to have another variable, setting which should reject queries for that node.

This can be useful if someone wants to manually run maintenance on the node like mysqldumps and don't want to tinker with load balancer etc.

Related discussion here http://www.mysqlperformanceblog.com/2013/05/02/galera-flow-control-in-percona-xtradb-cluster-for-mysql/#comment-1736303

[Alex Yurchenko (ayurchen)]

Raghavendra, how about read-only? Doesn't that fit the bill?

[Ovais Tariq (ovais-tariq)]

But then if the node rejects queries then how is mysqldump going to run?

[Ovais Tariq (ovais-tariq)]

I was also thinking about a use-case where I can do maintenance on the node such that the maintenance work does not affect other nodes in the cluster. For example i could be doing a backup on the node using xtrabackup and that can consume a lot of IO and thats going to affect the whole cluster. There can be other cases, for example running mysqldump can also cause issues that can affect other nodes because if one node can't keep up its going to affect other nodes.

[Alex Yurchenko (ayurchen)]

Ovais, so ideally there should be a command to desync the node from the cluster. However it is different from _rejecting_ queries, which is the topic of this ticket (which I think is Not A Good Idea).

[Raghavendra D Prabhu (raghavendra-prabhu)]

Yes, thats right. While #2 would be interesting to have, the
issue here is from load-balancer's/applications's perspective.

[Jervin R (revin)]

Raghu,

So what was the fix that was committed here? :-)

[Jervin R (revin)]

Ok found it, http://bazaar.launchpad.net/~raghavendra-prabhu/percona-xtradb-cluster/pxc-1179805/revision/442

So how would this affect the node participation in the cluster?

[Nirbhay Choubey (nirbhay)]

The documentation of wsrep_reject_queries says "This can be useful if someone wants to manually run maintenance on the node like mysqldump without need to change the settings on the load balancer". But I see that with this variable set mysqldump won't work at all (for obvious reasons?). What are the other use cases?

[Raghavendra D Prabhu (raghavendra-prabhu)]

@Nirbhay,

You are right in the mysqldump etc. cannot be run there. The reason for addition
of this changed from orginal description (and documentation needs to be updated
for it), it was, as I remember, was added for upgrades for cases where you needed node up (disabling queries) without disabling the provider, (though read-only suffices for that now).

[Shahriyar Rzayev (rzayev-sehriyar)]

Percona now uses JIRA for bug reports so this bug report is migrated to: https://jira.percona.com/browse/PXC-1347