replicate-ignore-db: reliability and network traffic

[Paolo Bernardi]

Hello,

I've setup a 3-node cluster and I'm trying to avoid replicating some DBs on some nodes.

To do that I've used the directive replicate-ignore-db, as per https://mariadb.com/kb/en/mariadb/mariadb-galera-cluster-known-limitations/

I have two questions about this:

1) Is it reliable? So far I've found out that the only (obvious) problem is that if I stop ignoring a DB the data previously replicated won't be automatically replicated to the node where it was previously ignored.

2) What about network traffic? If I ignore replication for a DB on a node, does the node still receive network traffic with replication data but silently discards it or it won't receive network traffic about it at all?

Thanks,

Paolo

[Philip Stoev]

Hello,

> 1) Is it reliable? So far I've found out that the only (obvious) problem
> is that if I stop ignoring a DB the data previously replicated won't be
> automatically replicated to the node where it was previously ignored.

You are generally correct, but there is more to it. If you intend to use
replicate-ignore-db only on some of your nodes and not on others, you now
have a cluster where not all nodes contain the same snapshot of the data,
which is a major break in the logic of what a cluster is supposed to be. For
example, you may end up in a situation where a node that only has some of
the data serves as a donor to a joining node that is supposed to have all of
the data.

> 2) What about network traffic? If I ignore replication for a DB on a node,
> does the node still receive network traffic with replication data but
> silently discards it or it won't receive network traffic about it at all?

If you use replicate-ignore-db, all network traffic is received on all
nodes, but only ignored on some. If you use binlog-ignore-db, replication
events for the ignored database are not generated at all.

Philip Stoev

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