MyRocks Limitations¶

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

• Online DDL
• ALTER TABLE ... EXCHANGE PARTITION
• SAVEPOINT
• Transportable tablespace
• Foreign keys
• Spatial indexes
• Fulltext indexes
• Gap locks
• Group Replication

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.

• 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/5.7/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.