MyRocks Limitations

The MyRocks storage engine lacks the following features compared to InnoDB:

You should also consider the following:

  • *_bin (e.g. latin1_bin) or binary collation should be used on CHAR and VARCHAR indexed columns. By default, MyRocks prevents creating indexes with non-binary collations (including latin1). You can optionally use it by setting rocksdb_strict_collation_exceptions to t1 (table names with regex format), but non-binary covering indexes other than latin1 (excluding german1) still require a primary key lookup to return the CHAR or VARCHAR column.

  • Either ORDER BY DESC or ORDER BY ASC is slow. This is because of “Prefix Key Encoding” feature in RocksDB. See http://www.slideshare.net/matsunobu/myrocks-deep-dive/58 for details. By default, ascending scan is faster and descending scan is slower. If the “reverse column family” is configured, then descending scan will be faster and ascending scan will be slower. Note that InnoDB also imposes a cost when the index is scanned in the opposite order.

  • MyRocks does not support operating as either a master or a slave in any replication topology that is not exclusively row-based. Statement-based and mixed-format binary logging is not supported. For more information, see Replication Formats.

  • As of 8.0.17, InnoDB supports multi-valued indexes. MyRocks does not support this feature.

  • When converting from large MyISAM/InnoDB tables, either by using the ALTER or INSERT INTO SELECT statements it’s recommended that you check the Data loading documentation and create MyRocks tables as below (in case the table is sufficiently big it will cause the server to consume all the memory and then be terminated by the OOM killer):

     SET session sql_log_bin=0;
     SET session rocksdb_bulk_load=1;
     ALTER TABLE large_myisam_table ENGINE=RocksDB;
     SET session rocksdb_bulk_load=0;
    
    .. warning::
    
     If you are loading large data without enabling :variable:`rocksdb_bulk_load`
     or :variable:`rocksdb_commit_in_the_middle`, please make sure transaction
     size is small enough. All modifications of the ongoing transactions are
     kept in memory.
    
  • The`XA protocol <https://dev.mysql.com/doc/refman/8.0/en/xa.html>`_ support, which allows distributed transactions combining multiple separate transactional resources, is an experimental feature in MyRocks: the implementation is less tested, it may lack some functionality and be not as stable as in case of InnoDB.

  • With partitioned tables that use the TokuDB or MyRocks storage engine, the upgrade only works with native partitioning.

    See also

    MySQL Documentation: Preparing Your Installation for Upgrade

    https://dev.mysql.com/doc/refman/8.0/en/upgrade-prerequisites.html

  • Percona Server for MySQL 8.0 and Unicode 9.0.0 standards have defined a change in the handling of binary collations. These collations are handled as NO PAD, trailing spaces are included in key comparisons. A binary collation comparison may result in two unique rows inserted and does not generate a`DUP_ENTRY` error. MyRocks key encoding and comparison does not account for this character set attribute.

  • In version 8.0.13-3 and later, MyRocks does not support explict DEFAULT value expressions.

  • Percona Server for MySQL 8.0.16 does not support encryption for the MyRocks storage engine. At this time, during an ALTER TABLE operation, MyRocks mistakenly detects all InnoDB tables as encrypted. Therefore, any attempt to ALTER an InnoDB table to MyRocks fails.

As a workaround, we recommend a manual move of the table. The following steps are the same as the ALTER TABLE ... ENGINE=... process:

  • Use ``SHOW CREATE TABLE ... `` to return the InnoDB table definition.
  • With the table definition as the source, perform a CREATE TABLE ... ENGINE=RocksDB.
  • In the new table, use INSERT INTO <new table> SELECT * FROM <old table>.

Note

With MyRocks and with large tables, it is recommended to set the session variable rocksdb_bulk_load=1 during the load to prevent running out of memory. This recommendation is because of the MyRocks large transaction limitation.