Remove old constraint

[squeaky-pl]

The table at this point looks like this:

CREATE TABLE `imapuid` (
  `created_at` datetime NOT NULL DEFAULT CURRENT_TIMESTAMP,
  `updated_at` datetime NOT NULL,
  `deleted_at` datetime DEFAULT NULL,
  `id` bigint NOT NULL AUTO_INCREMENT,
  `account_id` bigint NOT NULL,
  `message_id` bigint NOT NULL,
  `msg_uid` bigint NOT NULL,
  `folder_id` bigint NOT NULL,
  `is_draft` tinyint(1) NOT NULL DEFAULT '0',
  `is_seen` tinyint(1) NOT NULL DEFAULT '0',
  `is_flagged` tinyint(1) NOT NULL DEFAULT '0',
  `is_recent` tinyint(1) NOT NULL DEFAULT '0',
  `is_answered` tinyint(1) NOT NULL DEFAULT '0',
  `extra_flags` varchar(255) COLLATE utf8mb4_general_ci NOT NULL,
  `g_labels` text COLLATE utf8mb4_general_ci,
  PRIMARY KEY (`id`),
  UNIQUE KEY `folder_id` (`folder_id`,`msg_uid`,`account_id`),
  UNIQUE KEY `ix_imapuid_account_id_folder_id_msg_uid_desc` (`account_id`,`folder_id`,`msg_uid` DESC),
  KEY `message_id` (`message_id`),
  KEY `account_id_folder_id` (`account_id`,`folder_id`),
  KEY `ix_imapuid_created_at` (`created_at`),
  KEY `ix_imapuid_msg_uid` (`msg_uid`),
  KEY `ix_imapuid_deleted_at` (`deleted_at`),
  KEY `ix_imapuid_updated_at` (`updated_at`),
  CONSTRAINT `imapuid_ibfk_1` FOREIGN KEY (`account_id`) REFERENCES `imapaccount` (`id`) ON DELETE CASCADE ON UPDATE RESTRICT,
  CONSTRAINT `imapuid_ibfk_2` FOREIGN KEY (`message_id`) REFERENCES `message` (`id`) ON DELETE CASCADE ON UPDATE RESTRICT,
  CONSTRAINT `imapuid_ibfk_3` FOREIGN KEY (`folder_id`) REFERENCES `folder` (`id`) ON DELETE CASCADE ON UPDATE RESTRICT
) ENGINE=InnoDB AUTO_INCREMENT=912221389 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_general_ci

Note that the old unique constraint UNIQUE KEY folder_id (folder_id,msg_uid,account_id) on the three columns is confusingly called folder_id. That's what you get when you don't name your constraints explicitly.

After merging #870 we are sure that the old index/constraint is not used for retrieving data. So we can drop it, but...

It also powers the foreign key constraint on folder_id column, so I'm adding a one column index to power that constraint.

It's most probable that the KEY account_id_folder_id (account_id,folder_id) can be dropped now as well because it's a prefix of UNIQUE KEY ix_imapuid_account_id_folder_id_msg_uid_desc (account_id,folder_id,msg_uid DESC), but again I want to keep PRs focused and I'll investigate and open another PR.

Migration

-- Running upgrade e3cf974d07a5 -> ac2d6f8489bb

CREATE INDEX folder_id_new ON imapuid (folder_id);

DROP INDEX folder_id ON imapuid;

ALTER TABLE imapuid RENAME INDEX folder_id_new TO folder_id;

SET SQL_SAFE_UPDATES = 0; -- quirk of production MySQL shell configuration

UPDATE alembic_version SET version_num='ac2d6f8489bb' WHERE alembic_version.version_num = 'e3cf974d07a5';

I'll open a separate PR in the downstream with all the steps needed to perform in the downstream.

Based on PR #870

Full chain of PRs as of 2024-09-03

• PR Remove old constraint #872:
  drop-old-imapuid-constraint ➔ one-more-force-index
• PR Some more FORCE INDEX #870:
  one-more-force-index ➔ master