3.5 Changes in MySQL 8.4

Before upgrading to MySQL 8.4, review the changes described in the following sections to identify those that apply to your current MySQL installation and applications.

• Incompatible Changes in MySQL 8.4

• Changed Server Defaults

In addition, you can consult the resources listed here:

• Section 1.4, “What Is New in MySQL 8.4 since MySQL 8.0”

• MySQL 8.4 Release Notes

Incompatible Changes in MySQL 8.4

This section contains information about incompatible changes in MySQL 8.4.

• Spatial indexes.  When upgrading to MySQL 8.4.4 or later, it is recommended that you drop any spatial indexes beforehand, then re-create them after the upgrade is complete. Alternatively, you can drop and re-create such indexes immediately following the upgrade, but before making use of any of the tables in which they occur.

  For more information, see Section 13.4.10, “Creating Spatial Indexes”.

• WAIT_UNTIL_SQL_THREAD_AFTER_GTIDS() function removed.  The WAIT_UNTIL_SQL_THREAD_AFTER_GTIDS() SQL function, deprecated in MySQL 8.0 has been removed; attempting to invoke it now causes a syntax error. Use WAIT_FOR_EXECUTED_GTID_SET() instead.

• authentication_fido and authentication_fido_client no longer available on some platforms.  Due to upgrading the libfido2 library bundled with the server to version 1.13.0, which requires OpenSSL 1.1.1 or higher, the authentication_fido and authentication_fido_client authentication plugins are no longer available on Enterprise Linux 6, Enterprise Linux 7, Solaris 11, or SUSE Enterprise Linux 12.

• NULL disallowed for command-line options.  Setting server variables equal to SQL NULL on the command line is not supported. In MySQL 8.4, setting any of these to NULL is specifically disallowed, and attempting to do is rejected with an error.

  The following variables are excepted from this restriction: admin_ssl_ca, admin_ssl_capath, admin_ssl_cert, admin_ssl_cipher, admin_tls_ciphersuites, admin_ssl_key, admin_ssl_crl, admin_ssl_crlpath, basedir, character_sets_dir, ft_stopword_file, group_replication_recovery_tls_ciphersuites, init_file, lc_messages_dir, plugin_dir, relay_log, relay_log_info_file, replica_load_tmpdir, ssl_ca, ssl_capath, ssl_cert, ssl_cipher, ssl_crl, ssl_crlpath, ssl_key, socket, tls_ciphersuites, and tmpdir.

  See also Section 7.1.8, “Server System Variables”.

For additional information about changes in MySQL 8.4, see Section 1.4, “What Is New in MySQL 8.4 since MySQL 8.0”.

Changed Server Defaults

This section contains information about MySQL server system variables whose default values have changed in MySQL 8.4 as compared to MySQL 8.0.

System Variable	Old Default	New Default
InnoDB changes
innodb_adaptive_hash_index	ON	OFF
innodb_buffer_pool_in_core_file	ON	OFF
innodb_buffer_pool_instances	innodb_buffer_pool_size < 1GB: 1; otherwise: 8	innodb_buffer_pool_size <= 1GB: 1; otherwise: MIN( 0.5 * (innodb_buffer_pool_size / innodb_buffer_pool_chunk_size), 0.25 * number_of_cpus)
innodb_change_buffering	all	none
innodb_doublewrite_files	innodb_buffer_pool_instances * 2	2
innodb_doublewrite_pages	Value of innodb_write_io_threads	128
innodb_flush_method	fsync	O_DIRECT if supported, otherwise fsync
innodb_io_capacity	200	10000
innodb_io_capacity_max	MIN(2 * innodb_io_capacity, 2000)	2 * innodb_io_capacity
innodb_log_buffer_size	16777216	67108864
innodb_numa_interleave	OFF	ON
innodb_page_cleaners	4	Value of innodb_buffer_pool_instances
innodb_parallel_read_threads	4	MIN(number_of_cpus / 8, 4)
innodb_purge_threads	4	If number_of_cpus <= 16: 1; otherwise: 4
innodb_use_fdatasync	OFF	ON
Group Replication changes
group_replication_consistency	EVENTUAL	BEFORE_ON_PRIMARY_FAILOVER
group_replication_exit_state_action	READ_ONLY	OFFLINE_MODE
Temporary table changes
temptable_max_mmap	1073741824	0
temptable_max_ram	1073741824	3% of total memory within a range of 1-4 (GB)
temptable_use_mmap	ON	OFF

System Variable	Old Default	New Default

For more information about options or variables which have been added, see Option and Variable Changes for MySQL 8.4, in the MySQL Server Version Reference.

Although the new defaults are the best configuration choices for most use cases, there are special cases, as well as legacy reasons for using existing configuration choices. For example, some people prefer to upgrade to MySQL 8.4 with as few changes to their applications or operational environment as possible. We recommend to evaluate all the new defaults and use as many as you can.

The Performance Schema variables_info table shows, for each system variable, the source from which it was most recently set, as well as its range of values. This provides SQL access to all there is to know about a system variable and its values.