在我的服务https://simibat.ru/fftracker上，我有一些多（交界）表，例如角色成就表，它由两列带外键的列组成（其中一列也是复合主键），具有日期或其他相关内容的第三列。在成就表的示例中，它具有36+百万行，总大小约为1 GB，索引略低于500 MB。我知道没什么特别的。我担心的是指数的增长率。
在大约一周的时间内，索引将至少获得约400 MB额外的MB，而实际新数据最多（约10 MB）。经过表优化后，这400 MB变成了大约5 MB。每周进行优化并不是什么大问题，但是我很好奇是否有办法降低如此大的（毫无意义的）增长率，因为这似乎是一种适当的方法。
我知道，我可以尝试简单地删除成就ID的外键（因为它已经在我的所有查询中使用的复合索引中使用过），但是这感觉就像是逻辑向PHP的过度移植，而不是利用本机函数。
那么，有什么办法可以解决这个问题吗？
更新 要注意的另一件事：我正在运行INSERT ... ON重复密钥更新。会不会因此而更新索引，从而导致索引增长？
根据要求创建个表。我关心的表是ff__character_achievement（连接点），其余主要供参考（以防万一）。
CREATE TABLE `ff__character_achievement` (
`characterid` int(10) unsigned NOT NULL,
`achievementid` smallint(5) unsigned NOT NULL,
`time` date NOT NULL,
PRIMARY KEY (`characterid`,`achievementid`),
KEY `ach` (`achievementid`) USING BTREE,
CONSTRAINT `char_ach_ach` FOREIGN KEY (`achievementid`) REFERENCES `ff__achievement` (`achievementid`) ON DELETE CASCADE ON UPDATE CASCADE,
CONSTRAINT `char_ach_char` FOREIGN KEY (`characterid`) REFERENCES `ff__character` (`characterid`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci
CREATE TABLE `ff__achievement` (
`achievementid` smallint(5) unsigned NOT NULL,
`name` varchar(100) COLLATE utf8mb4_unicode_ci NOT NULL,
`category` varchar(30) COLLATE utf8mb4_unicode_ci DEFAULT NULL,
`subcategory` varchar(30) COLLATE utf8mb4_unicode_ci DEFAULT NULL,
`icon` varchar(150) COLLATE utf8mb4_unicode_ci DEFAULT NULL,
`howto` text COLLATE utf8mb4_unicode_ci,
`points` tinyint(3) unsigned DEFAULT NULL,
`title` varchar(50) COLLATE utf8mb4_unicode_ci DEFAULT NULL,
`item` varchar(100) COLLATE utf8mb4_unicode_ci DEFAULT NULL,
`itemicon` varchar(150) COLLATE utf8mb4_unicode_ci DEFAULT NULL,
`itemid` varchar(15) COLLATE utf8mb4_unicode_ci DEFAULT NULL,
PRIMARY KEY (`achievementid`),
KEY `name` (`name`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci
CREATE TABLE `ff__character` (
`characterid` int(10) unsigned NOT NULL,
`userid` int(10) unsigned DEFAULT NULL,
`serverid` tinyint(2) unsigned NOT NULL,
`name` varchar(50) COLLATE utf8mb4_unicode_ci NOT NULL,
`updated` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
`freecompanyid` bigint(20) unsigned DEFAULT NULL,
`biography` text COLLATE utf8mb4_unicode_ci,
`titleid` smallint(5) unsigned DEFAULT NULL,
`bio_avatar` varchar(66) COLLATE utf8mb4_unicode_ci NOT NULL,
`clanid` tinyint(2) unsigned NOT NULL,
`genderid` tinyint(1) unsigned NOT NULL,
`namedayid` smallint(3) unsigned NOT NULL,
`guardianid` tinyint(2) unsigned NOT NULL,
`cityid` tinyint(1) unsigned NOT NULL,
`fc_rankidprev` tinyint(2) unsigned DEFAULT NULL,
`fc_rankid` tinyint(2) unsigned DEFAULT NULL,
`fc_ranklvlupd` timestamp NULL DEFAULT NULL,
`fc_nextprom` text COLLATE utf8mb4_unicode_ci,
`gcrankid` tinyint(2) unsigned DEFAULT NULL,
`Alchemist` tinyint(3) unsigned DEFAULT NULL,
`Armorer` tinyint(3) unsigned DEFAULT NULL,
`Astrologian` tinyint(3) unsigned DEFAULT NULL,
`Bard` tinyint(3) unsigned DEFAULT NULL,
`BlackMage` tinyint(3) unsigned DEFAULT NULL,
`Blacksmith` tinyint(3) unsigned DEFAULT NULL,
`Botanist` tinyint(3) unsigned DEFAULT NULL,
`Carpenter` tinyint(3) unsigned DEFAULT NULL,
`Culinarian` tinyint(3) unsigned DEFAULT NULL,
`DarkKnight` tinyint(3) unsigned DEFAULT NULL,
`Dragoon` tinyint(3) unsigned DEFAULT NULL,
`Fisher` tinyint(3) unsigned DEFAULT NULL,
`Goldsmith` tinyint(3) unsigned DEFAULT NULL,
`Leatherworker` tinyint(3) unsigned DEFAULT NULL,
`Machinist` tinyint(3) unsigned DEFAULT NULL,
`Miner` tinyint(3) unsigned DEFAULT NULL,
`Monk` tinyint(3) unsigned DEFAULT NULL,
`Ninja` tinyint(3) unsigned DEFAULT NULL,
`Paladin` tinyint(3) unsigned DEFAULT NULL,
`RedMage` tinyint(3) unsigned DEFAULT NULL,
`Samurai` tinyint(3) unsigned DEFAULT NULL,
`Scholar` tinyint(3) unsigned DEFAULT NULL,
`Summoner` tinyint(3) unsigned DEFAULT NULL,
`Warrior` tinyint(3) unsigned DEFAULT NULL,
`Weaver` tinyint(3) unsigned DEFAULT NULL,
`WhiteMage` tinyint(3) unsigned DEFAULT NULL,
PRIMARY KEY (`characterid`,`name`) USING BTREE,
KEY `userid` (`userid`),
KEY `char_fc` (`freecompanyid`) USING BTREE,
KEY `genderid` (`genderid`),
KEY `clanid` (`clanid`),
KEY `guardianid` (`guardianid`),
KEY `namedayid` (`namedayid`),
KEY `cityid` (`cityid`),
KEY `serverid` (`serverid`),
KEY `gcrankid` (`gcrankid`),
KEY `titleid` (`titleid`),
KEY `fc_rankid` (`fc_rankid`),
KEY `fc_rankidprev` (`fc_rankidprev`),
CONSTRAINT `character_fcid` FOREIGN KEY (`freecompanyid`) REFERENCES `ff__freecompany` (`freecompanyid`) ON DELETE SET NULL ON UPDATE CASCADE,
CONSTRAINT `cityid` FOREIGN KEY (`cityid`) REFERENCES `ff__city` (`cityid`) ON DELETE CASCADE ON UPDATE CASCADE,
CONSTRAINT `clanid` FOREIGN KEY (`clanid`) REFERENCES `ff__clan` (`clanid`) ON DELETE CASCADE ON UPDATE CASCADE,
CONSTRAINT `fc_rankid` FOREIGN KEY (`fc_rankid`) REFERENCES `ff__freecompany_rank` (`rankid`) ON DELETE SET NULL ON UPDATE SET NULL,
CONSTRAINT `fc_rankidprev` FOREIGN KEY (`fc_rankidprev`) REFERENCES `ff__freecompany_rank` (`rankid`) ON DELETE SET NULL ON UPDATE SET NULL,
CONSTRAINT `gcrankid` FOREIGN KEY (`gcrankid`) REFERENCES `ff__grandcompany_rank` (`gcrankid`) ON DELETE SET NULL ON UPDATE SET NULL,
CONSTRAINT `genderid` FOREIGN KEY (`genderid`) REFERENCES `usersys__gender` (`genderid`) ON DELETE CASCADE ON UPDATE CASCADE,
CONSTRAINT `guardianid` FOREIGN KEY (`guardianid`) REFERENCES `ff__guardian` (`guardianid`) ON DELETE CASCADE ON UPDATE CASCADE,
CONSTRAINT `namedayid` FOREIGN KEY (`namedayid`) REFERENCES `ff__nameday` (`namedayid`) ON DELETE CASCADE ON UPDATE CASCADE,
CONSTRAINT `serverid` FOREIGN KEY (`serverid`) REFERENCES `ff__server` (`serverid`) ON DELETE CASCADE ON UPDATE CASCADE,
CONSTRAINT `titleid` FOREIGN KEY (`titleid`) REFERENCES `ff__achievement` (`achievementid`) ON DELETE SET NULL ON UPDATE SET NULL,
CONSTRAINT `userid` FOREIGN KEY (`userid`) REFERENCES `usersys__logins` (`userid`) ON DELETE SET NULL ON UPDATE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci ROW_FORMAT=COMPACT