Based on the performance testing that was conducted in
MDEV-17492, the InnoDB adaptive hash index could only help performance in specific, almost-read-only workloads. It could slow down all kinds of workloads (especially DROP TABLE, TRUNCATE TABLE, ALTER TABLE, or DROP INDEX operations), and it can become corrupted, causing crashes (such as MDEV-18815, MDEV-20203) and possibly data corruption. Furthermore, the adaptive hash index consumes space from the InnoDB buffer pool, which could hurt performance when the working set would almost fit in the buffer pool.
Given all this, it is best to remove the adaptive hash index. For now, we will change the default value of the build option WITH_INNODB_AHI to OFF and adjust tests.