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Percona XtraDB Cluster Limitations

The following limitations apply to Percona XtraDB Cluster:

  • Replication works only with InnoDB storage engine. Any writes to tables of other types, including system (mysql.*) tables, are not replicated. However, DDL statements are replicated in statement level, and changes to mysql.* tables will get replicated that way. So you can safely issue CREATE USER..., but issuing INSERT INTO mysql.user... will not be replicated. You can enable experimental MyISAM replication support using the wsrep_replicate_myisam variable.

  • Unsupported queries:

    • LOCK TABLES and UNLOCK TABLES is not supported in multi-master setups
    • Lock functions, such as GET_LOCK(), RELEASE_LOCK(), and so on
  • Query log cannot be directed to table. If you enable query logging, you must forward the log to a file:

    log_output = FILE
    

    Use general_log and general_log_file to choose query logging and the log file name.

  • Maximum allowed transaction size is defined by the wsrep_max_ws_rows and wsrep_max_ws_size variables. LOAD DATA INFILE processing will commit every 10 000 rows. So large transactions due to LOAD DATA will be split to series of small transactions.

  • Due to cluster-level optimistic concurrency control, transaction issuing COMMIT may still be aborted at that stage. There can be two transactions writing to the same rows and committing in separate Percona XtraDB Cluster nodes, and only one of the them can successfully commit. The failing one will be aborted. For cluster-level aborts, Percona XtraDB Cluster gives back deadlock error code:

    (Error: 1213 SQLSTATE: 40001  (ER_LOCK_DEADLOCK)).
    
  • XA transactions are not supported due to possible rollback on commit.

  • The write throughput of the whole cluster is limited by weakest node. If one node becomes slow, the whole cluster slows down. If you have requirements for stable high performance, then it should be supported by corresponding hardware.

  • The minimal recommended size of cluster is 3 nodes. The 3rd node can be an arbitrator.

  • InnoDB fake changes feature is not supported.

  • enforce_storage_engine=InnoDB is not compatible with wsrep_replicate_myisam=OFF (default).

  • The binlog_rows_query_log_events variable is not supported.

  • When running Percona XtraDB Cluster in cluster mode, avoid ALTER TABLE ... IMPORT/EXPORT workloads. It can lead to node inconsistency if not executed in sync on all nodes.

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