MySQL 8.0.17 Release Highlights: Cloning, JSON Multi‑Value Indexes, Optimizer Improvements, and More

MySQL officially released three maintenance versions (8.0.17, 5.7.27, 5.6.45) only 88 days after the previous GA release, adding bug fixes and new features such as Windows alert improvements for the 5.* series and several enhancements in 8.0.17.

1. Cloning – The MySQL Shell (updated in 8.0.16) can clone a running server to a new instance, useful for adding members to an InnoDB Cluster. The process can be automated after preparing an initial dump or backup.

2. JSON Multi‑Value Index – InnoDB now supports multi‑value indexes on JSON arrays, allowing efficient searches of array elements. Example index creation:

CREATE INDEX zips ON t1((CAST(data->'$.zipcode' AS UNSIGNED ARRAY)));

Queries can use functions like MEMBER OF() , JSON_CONTAINS() , and JSON_OVERLAPS() :

SELECT * FROM t1 WHERE 123 MEMBER OF(data->'$.data.zipcode');

3. JSON Schema Validation – New functions JSON_SCHEMA_VALID() and JSON_SCHEMA_VALIDATION_REPORT() enable validation of JSON documents against schemas and provide detailed error reports.

4. Optimizer Improvements – Subquery optimizations convert NOT EXISTS and NOT IN to anti‑joins, ensure complete predicates, and add CAST support for FLOAT/DOUBLE/REAL types to align explicit and implicit casts.

5. Volcano Iterator – Based on the Volcano model, this adds hash joins, better EXPLAIN/EXPLAIN ANALYZE, and expands support for window functions, aggregation, and duplicate removal.

6. New Collations – Added binary collation utf8mb4_0900_bin that uses the UTF‑8‑MB4 encoding without padding.

7. Replication Enhancements – Automated instance cloning for group replication recovery, improved cross‑version interoperability, encrypted binary log capture, and protocol compression for mysqlbinlog . Notably, cloning support for clusters and InnoDB Cluster is a major improvement.

8. Router – Added monitoring infrastructure and REST API, plus tighter integration with Group Replication for view‑change notifications.

9. MTR Test Component – MyISAM test cases moved to separate files, allowing MTR tests to run on servers without the MyISAM engine.

10. Miscellaneous – Hostnames up to 255 characters, mutex lock order checks to prevent deadlocks, partition‑aware parallel scan improvements, OS information added to client connection attributes, etc.

11. Deprecations and Removals – No features are removed in 8.0.17, but several are marked deprecated (e.g., named_pipe_full_access_group default, BINARY keyword for bin collations, integer display width, ZEROFILL, unsigned attributes for DECIMAL/FLOAT, && and || as synonyms, AUTO_INCREMENT on FLOAT/DOUBLE, etc.).

Overall, MySQL 8.0.17 continues to strengthen availability, especially for Group Replication, while introducing useful new capabilities such as server cloning and advanced JSON handling.