MyRocks limitations¶

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

Online DDL is not supported due to the lack of atomic DDL support.

* There is no `ALTER TABLE ... ALGORITHM=INSTANT` functionality

* A partition management operation only supports the `COPY` algorithms, which rebuilds the partition table and moves the data based on the new `PARTITION ... VALUE` definition. In the case of `DROP PARTITION`, the data not moved to another partition is deleted.

ALTER TABLE .. EXCHANGE PARTITION.
SAVEPOINT
Transportable tablespace
Foreign keys
Spatial indexes
Fulltext indexes
Gap locks
Group Replication
Partial Update of LOB in InnoDB

You should also consider the following:

All collations are supported 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 https://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.
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;

Expected output

.. warning::

   If you are loading large data without enabling :ref:`rocksdb_bulk_load`
   or :ref:`rocksdb_commit_in_the_middle`, please make sure transaction
   ize is small enough. All modifications of the ongoing transactions are
   kept in memory.

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
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.

Not supported on MyRocks¶

MyRocks does not support the following:

Operating as either a source or a replica 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.
Using multi-valued indexes. Implemented in Percona Server for MySQL 8.0.17, InnoDB supports this feature.
Using spatial data types .
Using the Clone Plugin and the Clone Plugin API. As of Percona Server for MySQL 8.0.17, InnoDB supports either these features.
Using encryption in tables. 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. For more information, see MyRocks Data Loading