MySQL native password authentication changes.  Beginning with MySQL 8.4.0, the deprecated mysql_native_password authentication plugin is no longer enabled by default. To enable it, start the server with --mysql-native-password=ON (added in MySQL 8.4.0), or by including mysql_native_password=ON in the [mysqld] section of your MySQL configuration file (added in MySQL 8.4.0).

For more information about enabling, using, and disabling mysql_native_password, see Section 8.4.1.1, “Native Pluggable Authentication”.

InnoDB system variable default value changes.  The default values for a number of server system variables relating to the InnoDB storage engine were changed in MySQL 8.4.0, as shown in the following table:

Clone plugin.  The clone plugin versioning requirement was relaxed to allow cloning between different point releases in the same series. In other words, only the major and minor version numbers must match when previously the point release number also had to match.

For example, clone functionality now permits cloning 8.4.0 to 8.4.14 and vice-versa.

SASL-based LDAP authentication on Windows.  On Microsoft Windows, the server plugin for SASL-based LDAP authentication is now supported. This means that Windows clients can now use GSSAPI/Kerberos for authenticating with the authentication_ldap_sasl_client plugin.

For more information, see SASL-Based LDAP Authentication (Without Proxying).

MySQL Replication: SOURCE_RETRY_COUNT change.  The default value for the SOURCE_RETRY_COUNT option of the CHANGE REPLICATION SOURCE TO statement was changed to 10. This means that, using the default values for this option and for SOURCE_CONNECT_RETRY (60), the replica waits 60 seconds between reconnection attempts, and keeps attempting to reconnect at this rate for 10 minutes before timing out and failing over.

This change also applies to the default value of the deprecated --master-retry-count server option. (You should use SOURCE_RETRY_COUNT, instead.)

For more information, see Section 19.4.9.1, “Asynchronous Connection Failover for Sources”.

MySQL Replication: tagged GTIDs.  The format of global transaction identifiers (GIDs) used in MySQL Replication and Group Replication has been extended to enable identification of groups of transactions, making it possible to assign a unique name to the GTIDs which belong to a specific group of transactions. For example, transactions containing data operations can easily be distinguished from those arising from administrative operations simply by comparing their GTIDs.

The new GTID format is UUID:TAG:NUMBER, where TAG is a string of up to 8 characters, which is enabled by setting the value of the gtid_next system variable to AUTOMATIC:TAG, added in this release (see the description of the variable for tag format and other information). This tag persists for all transactions originating in the current session (unless changed using SET gtid_next), and is applied at commit time for such transactions, or, when using Group Replication, at certification time. It is also possible to set gtid_next to UUID:TAG:NUMBER to set the UUID of a single transaction to an arbitrary value, along with assigning it a custom tag. The assignments of UUID and NUMBER are otherwise unchanged from previous MySQL releases. In either case, the user is responsible for making sure that the tag is unique to a given replication topology.

The original UUID:NUMBER format for GTIDs continues to be supported unchanged, as implemented in previous versions of MySQL; changes to existing replication setups using GTIDs are not required.

Setting gtid_next to AUTOMATIC:TAG or UUID:TAG:NUMBER requires a new TRANSACTION_GTID_TAG privilege which is added in this release; this is true both on the originating server as well as for the PRIVILEGE_CHECKS_APPLIER for the replica applier thread. This also means that an administrator can now restrict the use of SET @gtid_next=AUTOMATIC:TAG or UUID:TAG:NUMBER to a desired set of MySQL users or roles so that that only those users related to a given data or operational domain can commit new transactions with assigned tags.

The built-in functions GTID_SUBSET(), GTID_SUBTRACT(), and WAIT_FOR_EXECUTED_GTID_SET() are compatible with tagged GTIDs.

For more information, see the descriptions of the gtid_next system variable and the TRANSACTION_GTID_TAG privilege, as well as Section 19.1.4, “Changing GTID Mode on Online Servers”.

Replication: SQL_AFTER_GTIDS and MTA.  The START REPLICA statement option SQL_AFTER_GTIDS is now compatible with the multi-threaded applier. (Previously, when MTA was enabled and the user attempted to use this option, the statement raised the warning ER_MTA_FEATURE_IS_NOT_SUPPORTED, and the replica was switched to single-threaded mode.) This means that a replica which needs to catch up with missing transactions can now do so without losing the performance advantage from multithreading.

For more information, see Section 15.4.2.4, “START REPLICA Statement”, as well as the documentation for the replica_parallel_workers system variable. See also Section 19.2.3.2, “Monitoring Replication Applier Worker Threads”, and Section 25.7.11, “NDB Cluster Replication Using the Multithreaded Applier”.

Replication terminology backwards compatibility.  This release adds the --output-as-version option for mysqldump. This option allows you to create a dump from a MySQL 8.2 or newer server that is compatible with older versions of MySQL; its value, one of those listed here, determines the compatibility of replication terminology used in the dump:

See the description of this option for more information.

In addition a new value is added to those already allowed for the terminology_use_previous system variable. BEFORE_8_2_0 causes the server to print DISABLE ON SLAVE (now deprecated) instead of DISABLE ON REPLICA in the output of SHOW CREATE EVENT. The existing value BEFORE_8_0_26 now also has this effect in addition to those it already had previously.

The MySQL version number used in version-specific comments supports a major version consisting of one or two digits; this means that the entire version can be either five or six digits long. For more information about how this change affects handling of versioned comments in MySQL, see Section 11.7, “Comments”.

group_replication_set_as_primary() and DDL statements.  The group_replication_set_as_primary() function waits for ongoing DDL statements such as ALTER TABLE when waiting for all transactions to complete, prior to electing a new primary.

For more information, see the description of this function.

DDL and DCL statement tracking for group_replication_set_as_primary().  group_replication_set_as_primary() now waits for the following statements to complete before a new primary is elected:

These are in addition to those statements added in MySQL 8.1 or otherwise already supported in this regard. For more information, including a listing of all such statements supported in MySQL 8.3, see the description of the group_replication_set_as_primary() function.

Group Replication version compatibility.  Version compatibility for servers within groups has been extended as follows:

In-place downgrades of servers within groups are supported within the MySQL 8.4 LTS series. For example, a member of a group running MySQL 8.4.2 can be downgraded to MySQL 8.4.0.

Similarly, cross-version group membership is also supported within the 8.4 release series. For example, a server running MySQL 8.4.0 can join a group all of whose members currently run MySQL 8.4.2, as can a server running MySQL 8.4.3.

Group Replication variable defaults.  The default values of two server system variables relating to Group Replication have been changed in MySQL 8.4:

For more information, see Section 20.5.3.2, “Configuring Transaction Consistency Guarantees”, and Section 20.7.7, “Responses to Failure Detection and Network Partitioning”, as well as the descriptions of the variables listed.

Added a number of status variables specific to the Group Replication plugin that improve diagnosis and troubleshooting of network instabilities, providing statistics about network usage, control messages, and data messages for each group member.

See Section 20.9.2, “Group Replication Status Variables”, for more information.

As part of this work, a new MEMBER_FAILURE_SUSPICIONS_COUNT column was added to the Performance Schema replication_group_communication_information table. The contents of this column are formatted as a JSON array whose keys are group members ID and whose values are the number of times the group member has been considered suspect. See the description of this table for more information.

FLUSH_PRIVILEGES privilege.  A new privilege is added in MySQL 8.4.0 specifically to allow use of FLUSH PRIVILEGES statements. Unlike the RELOAD privilege, the FLUSH_PRIVILEGES privilege applies only to FLUSH PRIVILEGES statements.

In MySQL 8.4, the RELOAD privilege continues to be supported in this capacity to provide backwards compatibility.

When upgrading, a check is performed to see whether there are any users having the FLUSH_PRIVILEGES privilege; if there are none, any users having the RELOAD privilege are automatically assigned the new privilege as well.

If you downgrade from MySQL 8.4 (or later) to a version of MySQL which does not support the FLUSH_PRIVILEGES privilege, a user previously granted this privilege is unable to execute FLUSH PRIVILEGES statements unless the user has the RELOAD privilege.

OPTIMIZE_LOCAL_TABLE privilege.  MySQL 8.4.0 adds a new OPTIMIZE_LOCAL_TABLE privilege. Users must have this privilege to execute OPTIMIZE LOCAL TABLE and OPTIMIZE NO_WRITE_TO_BINLOG TABLE statements.

When upgrading from a previous release series, users having the SYSTEM_USER privilege are automatically granted the OPTIMIZE_LOCAL_TABLE privilege.

MySQL Enterprise Data Masking and De-Identification.  Data-masking components added support for specifying a dedicated schema to store the related internal table and masking functions. Previously, the mysql system schema provided the only storage option. The new component_masking.masking_database read-only variable enables setting and persisting an alternative schema name at server startup.

Flushing of data masking dictionaries.  The MySQL Enterprise Data Masking and De-Identification component now includes the ability to flush the data on the secondary or replica into memory. This can be done in either of the ways described here:

For more information, see Section 8.5, “MySQL Enterprise Data Masking and De-Identification”, and the descriptions of these items.

Automatic histogram updates.  MySQL 8.4.0 adds support for automatic updates of histograms. When this feature is enabled for a given histogram, it is updated whenever ANALYZE TABLE is run on the table to which it belongs. In addition, automatic recalculation of persistent statistics by InnoDB (see Section 17.8.10.1, “Configuring Persistent Optimizer Statistics Parameters”) also updates the histogram. Histogram updates continue to use the same number of buckets as they were originally specified with, if any.

You can enable this feature when specifying the histogram by including the AUTO UPDATE option for the ANALYZE TABLE statement. To disable it, include MANUAL UPDATE instead. MANUAL UPDATE (no automatic updates) is the default if neither option is specified.

For more information, see Histogram Statistics Analysis.

Added the tls-certificates-enforced-validation system variable, which permits a DBA to enforce certificate validation at server startup or when using the ALTER INSTANCE RELOAD TLS statement to reload certificates at runtime. With enforcement enabled, discovering an invalid certificate halts server invocation at startup, prevents loading invalid certificates at runtime, and emits warnings. For more information, see Configuring Certificate Validation Enforcement.

Added server system variables to control the amount of time MySQL accounts that connect to a MySQL server using LDAP pluggable authentication must wait when the LDAP server is down or unresponsive. The default timeout became 30 seconds for the following simple and SASL-based LDAP authentication variables:

Connection and response timeouts are configurable through the system variables on Linux platforms only. For more information, see Setting Timeouts for LDAP Pluggable Authentication.

Logging of the shutdown process was enhanced, with the addition of startup and shutdown messages for the MySQL server, plugins, and components. Such messages are now also logged for closing connections. These additions should facilitate troubleshooting and debugging problems, particularly in the event that the server takes an excessively long time to shut down.

For more information, see Section 7.4.2, “The Error Log”.

Additions to server startup and shutdown messages.  Added the following types of messages to the server startup and shutdown processes as noted in this list:

In addition, if the server was built using WITH_SYSTEMD, the server now includes every systemd message in the error log.

Added the SHOW PARSE_TREE statement, which shows the JSON-formatted parse tree for a SELECT statement. This statement is intended for testing and development use only, and not in production. It is available only in debug builds, or if MySQL was built from source using the CMake -DWITH_SHOW_PARSE_TREE option, and is not included or supported in release builds.

Thread pool plugin connection information.  Added thread pool connection information to the MySQL Performance Schema, as follows:

For more information, see Section 7.6.3, “MySQL Enterprise Thread Pool”, and Section 29.12.16, “Performance Schema Thread Pool Tables”.

Information Schema PROCESSLIST table usage.  Although the INFORMATION_SCHEMA.PROCESSLIST table was deprecated in MySQL 8.0.35 and 8.2.0, interest remains in tracking its usage. This release adds two system status variables providing information about accesses to the PROCESSLIST table, listed here:

Hash table optimization for set operations.  MySQL 8.2 improves performance of statements using the set operations EXCEPT and INTERSECT by means of a new hash table optimization which is enabled automatically for such statements, and controlled by setting the hash_set_operations optimizer switch; to disable this optimization and cause the optimizer to used the old temporary table optimization from previous versions of MySQL, set this flag to off.

The amount of memory allocated for this optimization can be controlled by setting the value of the set_operations_buffer_size server system variable; increasing the buffer size can further improve execution times of some statements using these operations.

See Section 10.9.2, “Switchable Optimizations”, for more information.

WITH_LD CMake option.  WITH_LD: Define whether to use the llvm lld or mold linker, otherwise use the standard linker. WITH_LD also replaces the USE_LD_LLD CMake option that was removed in MySQL 8.3.0.

MySQL Enterprise Firewall enhancements.  A number of enhancements were made since MySQL 8.0 to MySQL Enterprise Firewall. These are listed here:

For more information about firewall stored procedures, see MySQL Enterprise Firewall Stored Procedures.

Pluggable authentication.  Added support for authentication to MySQL Server using devices such as smart cards, security keys, and biometric readers in a WebAuthn context. The new WebAuthn authentication method is based on the FIDO and FIDO2 standards. It uses a pair of plugins, authentication_webauthn on the server side and authentication_webauthn_client on the client side. The server-side WebAuthn authentication plugin is included only in MySQL Enterprise Edition distributions.

Keyring migration.  Migration from a keyring component to a keyring plugin is supported. To perform such a migration, use the --keyring-migration-from-component server option introduced in MySQL 8.4.0, setting --keyring-migration-source to the name of the source component, and --keyring-migration-destination the name of the target plugin.

See Key Migration Using a Migration Server, for more information.

MySQL Enterprise Audit.  Added the audit_log_filter_uninstall.sql script to simplify removing MySQL Enterprise Audit.

New Keywords.  Keywords added in MySQL 8.4 since MySQL 8.0. Reserved keywords are marked with (R).

AUTO, BERNOULLI, GTIDS, LOG, MANUAL (R), PARALLEL (R), PARSE_TREE, QUALIFY (R), S3, and TABLESAMPLE (R).

Preemptive group replication certification garbage collection.  A system variable added in MySQL 8.4.0 group_replication_preemptive_garbage_collection enables preemptive garbage collection for group replication running in single-primary mode, keeping only the write sets for those transactions that have not yet been committed. This can save time and memory consumption. An additional system variable group_replication_preemptive_garbage_collection_rows_threshold (also introduced in MySQL 8.4.0) sets a lower limit on the number of certification rows needed to trigger preemptive garbage collection if it is enabled; the default is 100000.

In multi-primary mode, each write set in the certification information is required from the moment a transaction is certified until it is committed on all members, which makes it necessary to detect conflicts between transactions. In single-primary mode, where we need be concerned only about transaction dependencies, this is not an issue; this means write sets need be kept only until certification is complete.

It is not possible to change the group replication mode between single-primary and multi-primary when group_replication_preemptive_garbage_collection is enabled.

See Section 20.7.9, “Monitoring Group Replication Memory Usage with Performance Schema Memory Instrumentation”, for help with obtaining information about memory consumed by this process.

Sanitized relay log recovery.  In MySQL 8.4.0 and later, it is possible to recover the relay log with any incomplete transactions removed. The relay log is now sanitized when the server is started with --relay-log-recovery=OFF (the default), meaning that all of the following items are removed:

For more information, see the description of the relay_log_recovery server system variable.

MySQL upgrade history file.  As part of the installation process in MySQL 8.4.0 and later, a file in JSON format named mysql_upgrade_history is created in the server's data directory, or updated if it already exists. This file includes information about the MySQL server version installed, when it was installed, and whether the release was part of an LTS series or an Innovation series.

A typical mysql_upgrade_history file might look something like this (formatting adjusted for readability):

{
  "file_format":"1",

  "upgrade_history":
  [
    {
      "date":"2024-03-15 22:02:35",
      "version":"8.4.0",
      "maturity":"LTS",
      "initialize":true
    },

    {
      "date":"2024-05-17 17:46:12",
      "version":"8.4.1",
      "maturity":"LTS",
      "initialize":false
    }
  ]

}

In addition, the installation process now checks for the presence of a mysql_upgrade_info file (deprecated in MySQL 8.0, and is no longer used). If found, the file is removed.

mysql client --system-command option.  The --system-command option for the mysql client, available in MySQL 8.4.3 and later, enables or disables the system command.

This option is enabled by default. To disable it, use --system-command=OFF or --skip-system-command, which causes the system command to be rejected with an error.

group_replication_allow_local_lower_version_join system variable.  The group_replication_allow_local_lower_version_join system variable is deprecated, and setting it causes a warning (ER_WARN_DEPRECATED_SYNTAX_NO_REPLACEMENT) to be logged.

You should expect this variable to be removed in a future version of MySQL. Since the functionality enabled by setting group_replication_allow_local_lower_version_join is no longer useful, no replacement for it is planned.

Group Replication recovery metadata.  Group Replication recovery no longer depends on writing of view change events to the binary log to mark changes in group membership; instead, when all members of a group are MySQL version 8.3.0 or later, members share compressed recovery metadata, and no such event is logged (or assigned a GTID) when a new member joins the group.

Recovery metadata includes the GCS view ID, GTID_SET of certified transactions, and certification information, as well as a list of online members.

Since View_change_log_event no longer plays a role in recovery, the group_replication_view_change_uuid system variable is no longer needed, and so is now deprecated; expect its removal in a future MySQL release. You should be aware that no replacement or alternative for this variable or its functionality is planned, and develop your applications accordingly.

WAIT_UNTIL_SQL_THREAD_AFTER_GTIDS() function.  The WAIT_UNTIL_SQL_THREAD_AFTER_GTIDS() SQL function was deprecated in MySQL 8.0, and is no longer supported as of MySQL 8.2. Attempting to invoke this function now causes a syntax error.

Instead of WAIT_UNTIL_SQL_THREAD_AFTER_GTIDS(), it is recommended that you use WAIT_FOR_EXECUTED_GTID_SET(), which allows you to wait for specific GTIDS. This works regardless of the replication channel or the user client through which the specified transactions arrive on the server.

GTID-based replication and IGNORE_SERVER_IDS.  When global transaction identifiers (GTIDs) are used for replication, transactions that have already been applied are automatically ignored. This means that IGNORE_SERVER_IDS is not compatible with GTID mode. If gtid_mode is ON, CHANGE REPLICATION SOURCE TO with a non-empty IGNORE_SERVER_IDS list is rejected with an error. Likewise, if any existing replication channel was created with a list of server IDs to be ignored, SET gtid_mode=ON is also rejected. Before starting GTID-based replication, check for and clear any ignored server ID lists on the servers involved; you can do this by checking the output from SHOW REPLICA STATUS. In such cases, you can clear the list by issuing CHANGE REPLICATION SOURCE TO with an empty list of server IDs, as shown here:

CHANGE REPLICATION SOURCE TO IGNORE_SERVER_IDS = ();

See Section 19.1.3.7, “Restrictions on Replication with GTIDs”, for more information.

Binary log transaction dependency tracking and logging format.  Using writeset information for conflict detection has been found to cause issues with dependency tracking; for this reason, we now limit the usage of writesets for conflict checks to when row-based logging is in effect.

This means that, in such cases, binlog_format must be ROW, and MIXED is no longer supported.

expire_logs_days system variable.  The expire_logs_days server system variable, deprecated in MySQL 8.0, has been removed. Attempting to get or set this variable at runtime, or to start mysqld with the equivalent option (--expire-logs-days), now results in an error.

In place of expire_logs_days, use binlog_expire_logs_seconds, which allows you to specify expiration periods other than (only) in an integral number of days.

Wildcard characters in database grants.  The use of the characters % and _ as wildcards in database grants was deprecated in MySQL 8.2.0. You should expect for the wildcard functionality to removed in a future MySQL release and for these characters always to be treated as literals, as they are already whenever the value of the partial_revokes server system variable is ON.

In addition, the treatment of % by the server as a synonym for localhost when checking privileges is now also deprecated as of MySQL 8.2.0 and thus subject to removal in a future version of MySQL.

--character-set-client-handshake option.  The --character-set-client-handshake server option, originally intended for use with upgrades from very old versions of MySQL, is now deprecated and a warning is issued whenever it is used. You should expect this option to be removed in a future version of MySQL; applications depending on this option should begin migration away from it as soon as possible.

Nonstandard foreign keys.  The use of non-unique or partial keys as foreign keys is nonstandard, and is deprecated in MySQL. Beginning with MySQL 8.4.0, you must explicitly enable such keys by setting restrict_fk_on_non_standard_key to OFF, or by starting the server with --skip-restrict-fk-on-non-standard-key.

restrict_fk_on_non_standard_key is ON by default, which means that trying to use a nonstandard key as a foreign key in a CREATE TABLE or other SQL statement is rejected with ER_WARN_DEPRECATED_NON_STANDARD_KEY. Setting it to ON allows such statements to run, but they raise the same error as a warning.

Upgrades from MySQL 8.0 are supported even if there are tables containing foreign keys referring to non-unique or partial keys. In such cases, the server writes a list of warning messages containing the names of any foreign keys which refer to nonstandard keys.

Server options and variables removed.  A number of server options and variables supported in previous versions of MySQL have been removed in MySQL 8.4. Attempting to set any of them in MySQL 8.4 raises an error. These options and variables are listed here:

Obsolete replication options and variables.  A number of options and variables relating to MySQL Replication were deprecated in previous versions of MySQL, and have been removed from MySQL 8.4. Attempting to use any of these now causes the server to raise a syntax error. These options and variables are listed here:

Replication SQL syntax.  A number of SQL statements used in MySQL Replication which were deprecated in earlier versions of MySQL are no longer supported in MySQL 8.4. Attempting to use any of these statements now produces a syntax error. These statements can be divided into two groups those relating to source servers, and those referring to replicas, as shown here:

As part of this work, the DISABLE ON SLAVE option for CREATE EVENT and ALTER EVENT is now deprecated, and is superseded by DISABLE ON REPLICA. The corresponding term SLAVESIDE_DISABLED is also now deprecated,and no longer used in event descriptions such as in the Information Schema EVENTS table; REPLICA_SIDE_DISABLED is now shown instead.

All of the statements listed previously were removed from MySQL test programs and files, as well as from any other internal use.

In addition, a number of deprecated options formerly supported by CHANGE REPLICATION SOURCE TO and START REPLICA have been removed and are no longer accepted by the server. The removed options for each of these SQL statements are listed next.

Also as part of this work, the following server status variables, previously deprecated, have been removed. They are listed here, along with their replacements:

The variables just listed as removed no longer appear in the output of statements such as SHOW STATUS. See also Com_xxx Variables.

Plugins.  A number of plugins were removed in MySQL 8.4.0, and are listed here, along with any system variables and other features associated with them which were also removed or otherwise affected by the plugin removal:

Support for weak ciphers.  When configuring encrypted connections, MySQL 8.4.0 and later no longer allow specifying any cipher that does not meet the following requirements:

This has implications for setting the following system variables:

See the descriptions of these variables for their permitted values in MySQL 8.4, and more information.

INFORMATION_SCHEMA.TABLESPACES.  The INFORMATION_SCHEMA.TABLESPACES table, which was not actually used, was deprecated in MySQL 8.0.22 and has now been removed.

DROP TABLESPACE and ALTER TABLESPACE: ENGINE clause.  The ENGINE clause for DROP TABLESPACE and ALTER TABLESPACE statements was deprecated in MySQL 8.0. In MySQL 8.4, it is no longer supported, and causes an error if you attempt to use it with DROP TABLESPACE or ALTER TABLESPACE ... DROP DATAFILE. ENGINE is also no longer supported for all other variants of ALTER TABLESPACE, with the two exceptions listed here:

For more information, see the documentation for these statements.

LOW_PRIORITY with LOCK TABLES ... WRITE.  The LOW_PRIORITY clause of the LOCK TABLES ... WRITE statement had had no effect since MySQL 5.5, and was deprecated in MySQL 5.6. It is no longer supported in MySQL 8.4; including it in LOCK TABLES now causes a syntax error.

EXPLAIN FORMAT=JSON format versioning.  It is now possible to choose between 2 versions of the JSON output format used by EXPLAIN FORMAT=JSON statements using the explain_json_format_version server system variable introduced in this release. Setting this variable to 1 causes the server to use Version 1, which is the linear format which was always used for output from such statements in MySQL 8.2 and earlier. This is the default value and format in MySQL 8.4. Setting explain_json_format_version to 2 causes the Version 2 format to be used; this JSON output format is based on access paths, and is intended to provide better compatibility with future versions of the MySQL Optimizer.

See Obtaining Execution Plan Information, for more information and examples.

Capturing EXPLAIN FORMAT=JSON output.  EXPLAIN FORMAT=JSON was extended with an INTO option, which provides the ability to store JSON-formatted EXPLAIN output in a user variable where it can be worked with using MySQL JSON functions, like this:

mysql> EXPLAIN FORMAT=JSON INTO @myex SELECT name FROM a WHERE id = 2;
Query OK, 0 rows affected (0.00 sec)

mysql> SELECT JSON_EXTRACT(@myex, "$.query_block.table.key");
+------------------------------------------------+
| JSON_EXTRACT(@myex, "$.query_block.table.key") |
+------------------------------------------------+
| "PRIMARY"                                      |
+------------------------------------------------+
1 row in set (0.01 sec)

This option can be used only if the EXPLAIN statement also contains FORMAT=JSON; otherwise, a syntax error results. This requirement is not affected by the value of explain_format.

INTO can be used with any explainable statement with the exception of EXPLAIN FOR CONNECTION. It cannot be used with EXPLAIN ANALYZE.

For more information and examples, see Obtaining Execution Plan Information.

EXPLAIN FOR SCHEMA.  Added a FOR SCHEMA option to the EXPLAIN statement. The syntax is as shown here, where stmt is an explainable statement:

EXPLAIN [options] FOR SCHEMA schema_name stmt

This causes stmt to be run as if in the named schema.

FOR DATABASE is also supported as a synonym.

This option is not compatible with FOR CONNECTION.

See Obtaining Execution Plan Information, for more information.

Client comments preserved.  In MySQL 8.0, the stripping of comments from the mysql client was the default behavior; the default was changed to preserve such comments.

To enable the stripping of comments as was performed in MySQL 8.0 and earlier, start the mysql client with --skip-comments.

AUTO_INCREMENT and floating-point columns.  The use of the AUTO_INCREMENT modifier with FLOAT and DOUBLE columns in CREATE TABLE and ALTER TABLE statements was deprecated in MySQL 8.0; support for it is removed altogether in MySQL 8.4, where it raises ER_WRONG_FIELD_SPEC (Incorrect column specifier for column).

Before upgrading to MySQL 8.4 from a previous series, you must fix any table that contains a FLOAT or DOUBLE column with AUTO_INCREMENT so that the table no longer uses either of these. Otherwise, the upgrade fails .

mysql_ssl_rsa_setup utility.  The mysql_ssl_rsa_setup utility, deprecated in MySQL 8.0.34, has been removed. For MySQL distributions compiled using OpenSSL, the MySQL server can perform automatic generation of missing SSL and RSA files at startup. See Section 8.3.3.1, “Creating SSL and RSA Certificates and Keys using MySQL”, for more information.

MySQL Privileges.  Added the SET_ANY_DEFINER privilege for definer object creation and the ALLOW_NONEXISTENT_DEFINER privilege for orphan object protection. Together these privileges coexist with the deprecated SET_USER_ID privilege.

SET_USER_ID privilege.  The SET_USER_ID privilege, deprecated in MySQL 8.2.0, has been removed. use in GRANT statements now causes a syntax error

Instead of SET_USER_ID, you can use the SET_ANY_DEFINER privilege for definer object creation, and the ALLOW_NONEXISTENT_DEFINER privileges for orphan object protection.

Both privileges are required to produce orphaned SQL objects using CREATE PROCEDURE, CREATE FUNCTION, CREATE TRIGGER, CREATE EVENT, or CREATE VIEW.

--abort-slave-event-count and --disconnect-slave-event-count server options.  The MySQL server startup options --abort-slave-event-count and --disconnect-slave-event-count, formerly used in testing, were deprecated in MySQL 8.0, and have been removed in this release. Attempting to start mysqld with either of these options now results in an error.

mysql_upgrade utility.  The mysql_upgrade utility, deprecated in MySQL 8.0.16, has been removed.

mysqlpump utility.  The mysqlpump utility along with its helper utilities lz4_decompress and zlib_decompress, deprecated in MySQL 8.0.34, were removed. Instead, use mysqldump or MySQL Shell's dump utilities.

Obsolete CMake options.  The following options for compiling the server with CMake were obsolete and have been removed:

Removed Keywords.  Keywords removed in MySQL 8.4 since MySQL 8.0. Reserved keywords are marked with (R).

GET_MASTER_PUBLIC_KEY, MASTER_AUTO_POSITION, MASTER_BIND (R), MASTER_COMPRESSION_ALGORITHMS, MASTER_CONNECT_RETRY, MASTER_DELAY, MASTER_HEARTBEAT_PERIOD, MASTER_HOST, MASTER_LOG_FILE, MASTER_LOG_POS, MASTER_PASSWORD, MASTER_PORT, MASTER_PUBLIC_KEY_PATH, MASTER_RETRY_COUNT, MASTER_SSL, MASTER_SSL_CA, MASTER_SSL_CAPATH, MASTER_SSL_CERT, MASTER_SSL_CIPHER, MASTER_SSL_CRL, MASTER_SSL_CRLPATH, MASTER_SSL_KEY, MASTER_SSL_VERIFY_SERVER_CERT (R), MASTER_TLS_CIPHERSUITES, MASTER_TLS_VERSION, MASTER_USER, and MASTER_ZSTD_COMPRESSION_LEVEL.

Index prefixes in partitioning key.  Columns with index prefixes were allowed in the partitioning key for a partitioned table in MySQL 8.0, and raised a warning with no other effects when creating, altering, or upgrading a partitioned table. Such columns are no longer permitted in partitioned tables, and using any such columns in the partitioning key causes the CREATE TABLE or ALTER TABLE statement in they occur to be rejected with an error.

For more information, see Column index prefixes not supported for key partitioning.