Why MySQL 8.0 Table Rebuilds Slow Down and How to Fix It

MySQL 8.0 has a performance regression mainly manifested in table‑rebuilding operations whose execution efficiency drops significantly.

Core Issue

In MySQL 8.0 (especially 8.0.20 and later), executing ALTER TABLE ... FORCE and similar table‑rebuilding commands performs more than three times slower than in version 5.7. The problem was confirmed in July 2024 to be caused by an improper default value of the innodb_doublewrite_pages parameter.

Root Cause

Parameter change introduced a defect MySQL 8.0.20 introduced the innodb_doublewrite_pages parameter (default 4), which controls the number of pages written in each batch of InnoDB double‑write. The low value leads to:

I/O operations become more frequent

Double‑write buffer flush efficiency decreases

Disk sync cost rises significantly

Historical behavior difference In MySQL 5.7 the parameter did not formally exist, but its underlying implementation behaved as if the default were 128, resulting in higher I/O efficiency for table‑rebuilding.

Documentation and fix delay Although MySQL 8.4.0 corrected the default to 128, the 8.0 series retained the original default for LTS stability, requiring users to adjust the setting manually.

Affected Scenarios

The issue is especially noticeable in the following operations:

Using the INPLACE algorithm to rebuild tables (e.g., ALTER TABLE ... FORCE)

DDL operations involving massive data‑page writes

High‑concurrency write scenarios where double‑write buffer contention occurs

Official Recommendations

Temporary workaround : Set innodb_doublewrite_pages to 128 (requires instance restart)

Long‑term solution : Upgrade to MySQL 8.4+

Monitoring advice : Watch the Innodb_dblwr_pages_written and Innodb_dblwr_writes metrics for changes

(Note: the issue was fixed in MySQL 8.4 by adjusting the default value, but as of April 2025 MySQL 8.0 still retains the original default.)

Reference: https://jfg-mysql.blogspot.com/2025/04/performance-regression-in-mysql-80-fixed-in-84-easy-workaround.html