What’s New in MySQL 8.4? Key Feature Changes and Default Settings Explained

MySQL 8.4 has been officially released, and Oracle provides a complete set of documentation at

https://docs.oracle.com/cd/E17952_01/mysql-8.4-en/mysql-nutshell.html

.

Modified MySQL Features

Buffer Pool Hint : Calculated as innodb_buffer_pool_size / innodb_buffer_pool_chunk_size multiplied by 1/2.

CPU Hint : Set to one‑quarter of the number of available logical processors.

Cloning Plugin : Version‑control requirements are relaxed; only major and minor version numbers must match, allowing clones between different point releases (e.g., 8.4.0 ↔ 8.4.14).

Windows SASL‑based LDAP Authentication : A server plugin now supports SASL‑based LDAP authentication on Windows, enabling GSSAPI/Kerberos for the authentication_ldap_sasl_client plugin.

MySQL Replication : The default for SOURCE_RETRY_COUNT has been changed to 10, and SOURCE_CONNECT_RETRY defaults to 60 seconds.

Adjusted Default Values

Compared with MySQL 8.0, Oracle has updated many InnoDB defaults to better match modern hardware. For example, innodb_io_capacity is now 10 000 (suitable for SSDs) instead of 200.

MySQL’s native password authentication plugin is disabled by default in 8.4.0; to enable it, start the server with --mysql-native-password=ON or add mysql_native_password=ON to the [mysqld] section of my.cnf.

InnoDB System Variables – New Defaults vs. Old Defaults

InnoDB System Variable

New Default

Old Default

innodb_buffer_pool_in_core_file

OFF if MADV_DONTDUMP is supported, otherwise ON

ON

innodb_buffer_pool_instances

1 if innodb_buffer_pool_size ≤ 1 GiB; otherwise the minimum of the two calculated hints (range 1‑64)

8 (1 if size ≤ 1 GiB)

innodb_change_buffering

none

all

innodb_dedicated_server

ON (changes innodb_flush_method and makes innodb_redo_log_capacity CPU‑based)

OFF

innodb_adaptive_hash_index

OFF

ON

innodb_doublewrite_files

2 innodb_buffer_pool_instances * 2 innodb_doublewrite_pages

128

value of innodb_write_io_threads (default 4)

innodb_flush_method (Linux)

O_DIRECT if supported, otherwise fsync

sync

innodb_io_capacity

10000

200

innodb_io_capacity_max

2 * innodb_io_capacity

2 * innodb_io_capacity (minimum 2000)

innodb_log_buffer_size

67108864 (64 MiB)

16777216 (16 MiB)

innodb_numa_interleave

ON

OFF

innodb_page_cleaners

innodb_buffer_pool_instances

4

innodb_parallel_read_threads

available logical processors / 8 (minimum 4)

4

innodb_purge_threads

1 if logical processors ≤ 16, otherwise 4

4

innodb_read_io_threads

available logical processors / 2 (minimum 4)

4

innodb_use_fdatasync

ON

OFF

temptable_max_ram

3% of total memory (range 1‑4 GiB)

1 GiB

temptable_max_mmap

0 (means OFF)

1 GiB

temptable_use_mmap

OFF

ON

Conclusion

For local development, the conservative defaults can save resources, but production deployments often require manual tuning by DBAs or operations teams to achieve optimal performance. Oracle’s comprehensive updates aim to align defaults with modern hardware, simplifying configuration for most developers.