MySQL InnoDB cluster and group replication limitations

MySQL InnoDB cluster limitations:

01. A group can consist of maximum 9 servers. Attempting to add another server to a group with 9 members causes the request to join to be refused.

02. Limitations and issues described for multi-primary mode groups can also apply in single-primary mode clusters during a failover event, while the newly elected primary flushes out its applier queue from the old primary.

03. Individual transactions that result in GTID contents which are large enough that it cannot be copied between group members over the network within a 5 second window can cause failures in the group communication. To avoid this issue try and limit the size of your transactions as much as possible. For example, split up files used with LOAD DATA INFILE into smaller chunks.

04. Group Replication cannot currently make use of replication Event Checksums.

The certification process does not take into account gap locks, table lock, and named locks.

Setting a transaction isolation level to SERIALIZABLE configures Group Replication to refuse to commit the transaction.

05. Concurrent data definition statements and data manipulation statements executing against the same object but on different servers is not supported when using multi-primary mode.

06. Multi-primary mode groups (members all configured with group_replication_single_primary_mode=OFF) do not support tables with multi-level foreign key dependencies, specifically tables that have defined CASCADING foreign key constraints.

07. When a group is operating in multi-primary mode, SELECT .. FOR UPDATE statements can result in a deadlock.

08. Global replication filters cannot be used on a MySQL server instance that is configured for Group Replication, because filtering transactions on some servers would make the group unable to reach agreement on a consistent state.

09. InnodDB cluster is built on replication with GTID, so limitations of GTID are applicable to InnoDB cluster also.

Limitation of GTID:

• No support for non transactional engine such as MyISAM.
• CREATE TABLE ... SELECT.
• ALTER TABLE ... ADD, if the column has an expression default value.
• Binlog_format is set to STATEMENT, and CREATE TEMPORARY TABLE and DROP TEMPORARY TABLE statements cannot be used inside transactions, procedures, functions, and triggers when GTIDs are in use on the server (that is, when the enforce_gtid_consistency system variable is set to ON).
• sql_slave_skip_counter is not supported when using GTIDs. If you need to skip transactions, use the value of the master's gtid_executed variable instead.
• IGNORE_SERVER_IDS option of the CHANGE MASTER TO statement is deprecated when using GTIDs.

Ref.:

https://dev.mysql.com/doc/refman/8.0/en/group-replication-limitations.html
https://dev.mysql.com/doc/refman/8.0/en/replication-gtids-restrictions.html
https://dev.mysql.com/doc/refman/8.0/en/group-replication-frequently-asked-questions.html
https://dev.mysql.com/doc/refman/8.0/en/group-replication-requirements.html