Key Features of MySQL 8.0.21 Release

MySQL 8.0.21 was released with a set of important feature updates and bug fixes. The release replaces terminology such as Master/Slave and provides detailed release notes on the official site.

InnoDB

• Added a global configuration to enable or disable the redo log (WL#13795). Dynamic redo log start/stop can improve write speed but may increase risk of data loss if the server crashes. It is useful when loading initial data: disable redo log, load data, then re‑enable it.

ALTER INSTANCE ENABLE|DISABLE INNODB REDO_LOG;

• Tablespace filename validation becomes optional via --innodb-validate-tablespace-paths (ON|OFF) , reducing startup time on HDD systems when file moves are not expected.

• Lock system optimization (WL#10314) replaces a single latch protecting all queues with finer‑grained latches, allowing each table and row to be treated as a resource and improving scalability.

• All InnoDB tablespaces are now limited to known directories (datadir, innodb_data_home_dir, innodb_directories, innodb_undo_directory) to prevent accidental file creation in arbitrary locations.

• Undo DDL now supports ACID (WL#11819). Undo tablespace performance and safety are improved; CREATE/TRUNCATE operations are logged to the redo log, avoiding extra checkpoints and fixing issues with CREATE, DROP, and TRUNCATE.

JSON

• Added JSON_VALUE function (WL#12228) to simplify indexing of JSON values. It extracts a value from a JSON document and returns it as a specified type.

SELECT JSON_VALUE('{"name": "Evgen"}', '$.name')

Returns the unquoted string Evgen as VARCHAR(512) .

SELECT JSON_VALUE('{"price": 123.45}', '$.price' RETURNING DECIMAL(5,2))

Returns the numeric value 123.45 as DECIMAL(5,2) .

SQL DDL

• CREATE TABLE … AS SELECT is now an atomic statement (WL#13355), fixing cases where CREATE succeeded but SELECT rolled back.

Optimizer

• New optimizer parameter to disable limit optimization (WL#13929). prefer_ordering_index is enabled by default, allowing the optimizer to switch from a non‑ordering index to a grouping/sorting index when a LIMIT clause is present.

• Semi‑join support for single‑table UPDATE and DELETE (WL#6057) enables these statements to benefit from the optimizer like regular SELECTs.

// Previously these statements could not use semijoin and were slower
UPDATE t1 SET x=y WHERE z IN (SELECT * FROM t2);
DELETE FROM t1 WHERE z IN (SELECT * FROM t2);
// These can now use semijoin and are faster
SELECT x FROM t1 WHERE z IN (SELECT * FROM t2);

Group Replication

• Reduced minimum cache size: group_replication_message_cache_size lowered from 1 GB to 128 MB (WL#13979), allowing deployment on low‑memory hosts.

• Added ability to specify which endpoints may resume traffic during recovery (WL#13767), improving control over network traffic after failures.

• XCom can now be compiled with C++ (WL#13842), leveraging modern language features.

• Important group‑replication log messages are now classified as system messages (WL#13769), ensuring they are always recorded.

• START GROUP_REPLICATION now accepts USER, PASSWORD, DEFAULT_AUTH, and PLUGIN_DIR as optional parameters (WL#13768), avoiding the need to store credentials in files.

• group_replication_autorejoin_tries default increased from 0 to 3 (WL#13706) to enable automatic recovery from network partitions.

• group_replication_member_expel_timeout default increased from 0 to 5 seconds (WL#13773) to reduce unnecessary expulsions on transient network issues.

• Binary log checksum support added for group replication (WL#9038), allowing automatic verification of binlog integrity.

X Plugin

• --mysqlx-bind-address now supports multiple values (WL#12715), enabling the server to bind to several IP addresses.

Router

• User‑configurable log file name (WL#13838) allows logs to be written to a file other than mysqlrouter.log and redirects console output to stdout.

• Support for hiding nodes from applications (WL#13787) adds a metadata attribute to mark instances as hidden, preventing them from receiving client traffic while still being part of the InnoDB Cluster.

Other

• CREATE/ALTER USER now supports a JSON description attribute (WL#13562), storing arbitrary metadata in the user_attributes column of mysql.user .

ALTER USER foo ATTRIBUTE '{ "free_text" : "This is a free form text" }';

• Separate TLS certificate sets are now available for admin connections (WL#13850), allowing distinct certificates for management and regular client ports.

• Asynchronous client compression protocol added (WL#13510) to reduce cross‑data‑center traffic.

• Secure client library LOAD DATA LOCAL INFILE path/directory restrictions (WL#13168) let administrators define allowed and disallowed locations.

Deprecations

• Prefix‑key support in partition functions is deprecated (WL#13588) and will become an error in future releases.

Thank you for using MySQL!