MySQL INFORMATION_SCHEMA 漏洞

Question

based on this post in phpmyadmin (that i am the owner)

i dont know what happen with INFORMATION_SCHEMA Table.

https://github.com/phpmyadmin/phpmyadmin/issues/16378#issuecomment-703820551

I've been digging a bit deeper on the subject and it seems that everything points to a mysql server problem and the "INFORMATION_SCHEMA".

DROP TABLE IF EXISTS `Tbl_Lis_Agencias`;
CREATE TABLE IF NOT EXISTS `Tbl_Lis_Agencias` (
  `IdAgency` int(3) UNSIGNED ZEROFILL NOT NULL AUTO_INCREMENT,
  `AgencyCodU` int(3) UNSIGNED ZEROFILL NOT NULL DEFAULT '000',
  `AgencyName` varchar(40) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci DEFAULT NULL,
  `Agency_Order` int UNSIGNED DEFAULT NULL,
  `AgencyStatus` int UNSIGNED NOT NULL DEFAULT '1',
  PRIMARY KEY (`IdAgency`),
  UNIQUE KEY `IdAgency` (`IdAgency`),
  UNIQUE KEY `Agency_Order` (`Agency_Order`),
  UNIQUE KEY `AgencyName` (`AgencyName`),
  KEY `xAgencyStatus` (`AgencyStatus`)
) ENGINE=InnoDB AUTO_INCREMENT=12345 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;

INSERT INTO `Tbl_Lis_Agencias` VALUES
(001, 001, 'Panama', 1, 1),
(002, 020, 'Aguadulce', 2, 1),
(003, 080, 'David', 3, 1),
(004, 010, 'Vacamonte', 4, 1);

I have used the Mysql WorkBench, to execute the following query:

SELECT `AUTO_INCREMENT`
FROM  INFORMATION_SCHEMA.TABLES
WHERE TABLE_SCHEMA = 'DB_LIS'
AND   TABLE_NAME   = 'Tbl_Lis_Agencias';

**and output: no matter how many times you run the update of auto_increment to the value: 5 **

ALTER TABLE Tbl_Lis_Agencias AUTO_INCREMENT =5;

but when i go to table option in tab option in software; not code:

### this must be a joke ... what's going on here ???

Answer 1

MySQL 8.0 tries to cache the statistics about tables, but there seem to be some bugs in the implementation. Sometimes it shows table statistics as NULL, and sometimes it shows values, but fails to update them as you modify table data.

See https://bugs.mysql.com/bug.php?id=83957 for example, a bug that discusses the problems with this caching behavior.

You can disable the caching. It may cause queries against the INFORMATION_SCHEMA or SHOW TABLE STATUS to be a little bit slower, but I would guess it's no worse than in versions of MySQL before 8.0.

SET GLOBAL information_schema_stats_expiry = 0;

The integer value is the number of seconds MySQL keeps statistics cached. If you query the table stats, you may see old values from the cache, until they expire and MySQL refreshes them by reading from the storage engine.

The default value for the cache expiration is 86400, or 24 hours. That seems excessive.

See https://dev.mysql.com/doc/refman/8.0/en/server-system-variables.html#sysvar_information_schema_stats_expiry