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Galera cluster latency issues

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  • Galera cluster latency issues

    I ran into a seemingly well written article today on setting up a Galera cluster with master-master replication on Ubuntu. The questions that appear unanswered to me

    a. Suppose I setup a cluster with 5 servers scattered across the four corners of the globe. Will the efforts at keeping them in synch result in a significant latency issue that will be to the detriment of the system as a whole?
    b. Am I write in thinking that provided I get Galera up and running properly I can pretty much leave my PHP PDO code unchanged in the blissful assumption that Galera is handling replication so well that I have a cast iron guarantee of being able to access the same data on each server?

  • #2
    So as Galera is called "virtually synchronous replication" you may expect that the latency between the nodes will affect the whole cluster performance. It also applies (however in a bit different extent) for the individual nodes capabilities as the slowest node may again affect whole cluster operations.
    Regarding accessing same data on each node (server) - see the causal reads setting if you really need it.
    From my experience you will want rather reliable WAN links between the nodes.
    Also since Galera 3 there are improvements to handle WAN scenarios better:
    http://www.mysqlperformanceblog.com/...ying-galera-3/

    Some more hopefully interesting lectures for you:
    http://www.mysqlperformanceblog.com/...r-replication/
    http://www.mysqlperformanceblog.com/...tradb-cluster/
    http://www.mysqlperformanceblog.com/...ion-cross-wan/

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