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Poor Galera performance

Sergey KurkinSergey Kurkin EntrantCurrent User Role Beginner

I'm new to Galera, however I was able to setup 3 node cluster
(using MariaDB or Percona). My problem is that when I go from single node to Galera (for example
single node with wsrep* in my.cnf) performance have decreased about 10 fold (without wsrep node
1000% faster).
What may be wrong with my Galera setup ?
thank you,


  • dbennett455dbennett455 Entrant Current User Role Beginner
    Hi Sergey,

    Can you post your my.cnf/wsrep.cnf configurations?

  • Sergey KurkinSergey Kurkin Entrant Current User Role Beginner
    Of course. I forgot to say - this slow down only for write queries. Galera reading performance is good. In production environment I have good hardware (Xeon cpu, RAID and so on). I made experiments on Virtual machines (usual Celeron CPU, SATA HDD) and have found the same slow down at transition from stand-alone server to Galera.

    port = 3306
    socket = /var/run/mysqld/mysqld.sock

    socket = /var/run/mysqld/mysqld.sock
    #nice = 0

    wsrep_provider_options="gcache.size=2G; gcache.page_size=1G;gcs.fc_limit = 256; gcs.fc_factor = 0.99;"
    wsrep_slave_threads= 32
    auto_increment_offset = 1
    auto_increment_increment = 1
    wsrep_auto_increment_control = 0

    user = mysql
    pid-file = /var/run/mysqld/
    socket = /var/run/mysqld/mysqld.sock
    port = 3306
    basedir = /usr
    datadir = /var/lib/mysql
    tmpdir = /tmp
    lc-messages-dir = /usr/share/mysql
    collation-server = utf8_general_ci
    init-connect='SET NAMES utf8;'
    #init-connect='SET GLOBAL sql_mode="";'
    #init-connect='SET SESSION sql_mode="";'
    #init-connect='SET sql_mode="";'
    default-storage-engine = InnoDB
    character-set-server = utf8
    bind-address =
    #bind-address =

    thread_handling = pool-of-threads
    #thread_pool_high_prio_mode = transactions
    thread_pool_size = 16
    thread-cache-size = 400

    # MyISAM #
    key-buffer-size = 32M
    myisam-recover = FORCE,BACKUP

    # SAFETY #
    max-allowed-packet = 16M
    max-connect-errors = 1000000

    tmp-table-size = 32M
    max-heap-table-size = 32M
    query-cache-type = 0
    query-cache-size = 0
    max-connections = 1000
    open-files-limit = 65535
    table-definition-cache = 4096
    table-open-cache = 1900

    # INNODB #
    innodb-log-files-in-group = 2
    innodb-log-file-size = 128M
    innodb-flush-log-at-trx-commit = 1
    innodb-file-per-table = 1
    innodb-buffer-pool-size = 32G

    # LOGGING #
    log-error = /var/log/mysql/mysql-error.log
    #log-queries-not-using-indexes = 1
    #slow-query-log = 1
    #slow-query-log-file = /var/log/mysql/mysql-slow.log

    max_allowed_packet = 16M

    #no-auto-rehash # faster start of mysql but no tab completition

    key_buffer = 16M

    # * IMPORTANT: Additional settings that can override those from this file!
    # The files must end with '.cnf', otherwise they'll be ignored.
    !includedir /etc/mysql/conf.d/
  • dbennett455dbennett455 Entrant Current User Role Beginner
    Hi Sergey,

    Thanks for posting. Here's a couple of performance tips for starters:

    * wsrep_slave_threads= 32

    From the README-wsrep file, this number should be low per CPU core. To be safe, I'd say start with 2 threads per core, Use

    cat /proc/cpuinfo | grep -c '^processor\s*:'

    and multiply by 2 for a starting value. You may want to reduce this to 1 thread per core or lower.

    * wsrep_provider_options="gcache.size=2G; gcache.page_size=1G;gcs.fc_limit = 256; gcs.fc_factor = 0.99;"

    Refer to this guide for these values.


    - rule out a network bandwidth issue, use the iperf tool ( to measure the bandwidth between your nodes.

    - make sure that values aren't being overridden by configuration files in your /etc/mysql/conf.d directory.
  • Sergey KurkinSergey Kurkin Entrant Current User Role Beginner
    Thank you, Dave.

    All is ok on my system, including bandwith issue.
    No one can explain me why Galera so slow on write queries....
    (at least for query "insert into test.tmptable values ('test1','test2','test3')")
  • dbennett455dbennett455 Entrant Current User Role Beginner
    Hi Sergey,

    Can you provide some general specifications on the write operation? table size, row length, column definition, indexes and avg/max write operations per second would help. I could put together a randgen simulation with your configuration above.

  • dbennett455dbennett455 Entrant Current User Role Beginner
    One other question, what is your overall transaction size?
  • taka-htaka-h Contributor Current User Role Beginner

    Within my environment, the most dominant tuning parameter was repl.commit_order(although we may not change this parameter)

    This configuration seems to serialize the transaction in each replicated nodes, scalability for cuncurrent transaction may lost significantly
    This occurred even when the cluster node is just one node.

    To judge whether the problem is caused by galera cluster or not, just to turn off all the wsrep configuration(comment out or so on) and benchmark may help you.

    thank you.
  • Sergey KurkinSergey Kurkin Entrant Current User Role Beginner
    Thank you very much.

    Yes, I made benchmarks (before posting) with VMWare environment (Ubuntu and so on).
    Expert from SeveralNines made his benchmark with sysbench (olpt), also using VMWare and he
    have got ~400% slow down.

    So, from my experience I can't view database clustering as good solution for performance increase.
    For example if I will setup 4 nodes I will have performance of 1 node.
    If I will setup for example 20 nodes I don't know value of performance I will have. May be I will have 4xperformance of 1 node,
    but may be less than 4x.
  • taka-htaka-h Contributor Current User Role Beginner

    * scaling for read traffic is very effective and easy(this almost depends on CPU resource)
    * scaling for write seems difficult and I also need the effective and simple strategy.

    thank you
  • dbennett455dbennett455 Entrant Current User Role Beginner
    In most scenarios, moving from a virtualized environment to dedicated hardware would be a logical first scaling step prior to considering multi-master replication. So a performance benchmark of a pxc/galera multi-master virtualized environment may not be practical. Aside from overall performace scaling, there is also the high availability use case in which vitalization may play a role. That being said, there are some tuning steps regarding threading and transaction size that may also be effecting your test results.

    If you're running a PXC cluster as a VM guest you should definitely reduce your slave threads to match 2x max cores (or lower) defined in the guest. Also, if you are running very large write transactions such as multiple inserts, updates or to see if there's a large memory allocation and/or swapping occurring.

    There are some tuning parameters for this case. If a large writeset is created by a which will set limits on the transaction size. These parameters will cause replication rejections which will be logged. If they are, you need to modify your code to split up the apps large writesets.
  • Sergey KurkinSergey Kurkin Entrant Current User Role Beginner
    Thank you. It is very interesting.
  • krunalbauskarkrunalbauskar Advisor Inactive User Role Novice
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