Wrong auto_increment value on select - mysql

Question

I'm running MySQL 8 and whenever I run
SELECT AUTO_INCREMENT
FROM INFORMATION_SCHEMA.TABLES
WHERE TABLE_SCHEMA = 'test'
AND TABLE_NAME = 'table';
I get the wrong auto_increment value. Straightforward exemple :
ALTER TABLE test.lieux auto_increment = 6;
SELECT AUTO_INCREMENT
FROM INFORMATION_SCHEMA.TABLES
WHERE TABLE_SCHEMA = 'test'
AND TABLE_NAME = 'lieux';
Return AUTO_INCREMENT of 4.
I even tried inserting a row after my auto_increment altering, it was indeed inserted with a PK value of 6, but the SELECT statement still returned me an A_I value of 4.
Is there something wrong with my schema or did I misunderstand the SELECT AUTO_INCREMENT statement ?

Answer 1

This happens because the table statistics are cached beginning with Mysql 8.
To see the current value of the cache, execute -
show variables like 'information_schema_stats_expiry'
/* output (For mysql 8+, default cache is 86400 seconds = 1 day) */
+---------------------------------+-------+
| Variable_name | Value |
+---------------------------------+-------+
| information_schema_stats_expiry | 86400 |
+---------------------------------+-------+
To get the latest AUTO_INCREMENT value, you should update the expiry time to bypass the cache.
There are 2 ways you can do this.
1. For the current session
To update the cache value for the current session alone, as suggested in the comments, execute
SET ##SESSION.information_schema_stats_expiry = 0;
2. Globally
If you wish to disable the cache altogether, use
SET PERSIST information_schema_stats_expiry = 0
IMO, a default cache of 1 day is an overkill and totally unneeded. A cache of about 5 mins (300s) should generally suffice.
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