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Percona XtraDB Cluster has many excellent features that make it easy to implement mysql clusters. But don't ignore some of its limitations. If you can't accept it, or if your application or database (such as using the memory engine) can't adjust the limits, then PXC is not appropriate for you. What are the restrictions, which are described below.

1. Storage engine:

   PXC-based replication applies only to the InnoDB storage engine.

   does not replicate any writes to tables from other storage engines, including system tables such as mysql.* tables.

  , isn't it impossible to synchronize the creation of users? On this question. It is supported for statements based on DDL mode.

   DDL statements are implemented in a statement-based manner (that is, without using row mode).

All DDL-style changes made by    to the mysql.* table are replicated at the statement level.

   such as: CREATE USER... DDL is copied (statement level)

     INSERT INTO mysql.user... Myisam storage engine, will not be replicated because non-DDL statements

Of course,      can also configure wsrep_replicate_myisam parameter implementation (not recommended)

2. Unsupported queries:

   LOCK TABLES does not support UNLOCK TABLES and LOCK TABLES in multi-master mode

   locking features, such as GET_LOCK (), RELEASE_LOCK (), etc., are also not supported.

3. The query log cannot be directed to the table:

   if query logging is enabled, the log must be forwarded to a file

   uses general_log and general_log_file to select query log records and log file names

   log_output = file

4. Maximum transaction size:

The maximum transaction size allowed by    is defined by the wsrep_max_ws_rows and wsrep_max_ws_size variables

The    LOAD DATA INFILE method handles commit for every 10000 rows. For large transactions, many small transactions will be broken down

5. Cluster optimistic concurrency control:

The    PXC cluster uses optimistic concurrency control, and transaction COMMIT may still be aborted at this stage

   can have two transactions that write to the same row and commit in a separate Percona XtraDB cluster node, and only one of them commits successfully.

   failure will be aborted. For cluster-level aborts, the Percona XtraDB cluster returns a deadlock error code:

     (Error: 1213 SQLSTATE: 40001 (ER_LOCK_DEADLOCK).

6. Due to possible commit rollback, XA transactions are not supported: 7. Hardware configuration shortboard restrictions:

   the write throughput of the entire cluster is limited by the weakest nodes. If one node slows down, the whole cluster slows down.

   if you have requirements for stable high performance, then it should be supported by the appropriate hardware.

8. The recommended minimum cluster size is 3 nodes. The third node can be the arbitrator. 9. The InnoDB false change function is not supported. 10. Enforce_storage_engine=InnoDB is not compatible with wsrep_replicate_myisam=OFF (default). 11. Binlog_rows_query_log_events variable is not supported. Avoid ALTER TABLE under high load. IMPORT / EXPORT

When    runs a Percona XtraDB cluster in cluster mode, avoid ALTER TABLE. IMPORT / EXPORT workload.

If    is not executed synchronously on all nodes, it may result in node inconsistency.

Reference link: https://www.percona.com/doc/percona-xtradb-cluster/LATEST/limitation.html

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