The version, mysql is InnoDB 5.6.10-log, pt-online-schema-change 3.1.0. table info is

`email` varchar(225) COLLATE utf8mb4_unicode_ci DEFAULT NULL,
`uid` varchar(255) COLLATE utf8mb4_unicode_ci DEFAULT NULL,
`hotel_brand_id` int(11) DEFAULT NULL,

UNIQUE KEY `index_membership_customers_on_uid_and_hotel_brand_id` (`uid`,`hotel_brand_id`),

My purpose is to add a unique index,

pt-online-schema-change --recursion-method=none --nocheck-unique-key-change h=$DATABASE_HOST,D=$DATABASE,t=$TABLE,u=$DATABASE_USER,p=$DATABASE_PASSWORD   --alter "ADD UNIQUE INDEX index_membership_customers_on_email_and_hotel_brand_id (email, hotel_brand_id)"   --$RUN --alter-foreign-keys-method=auto

then I met the unique index length issue(https://stackoverflow.com/questions/1814532/mysql-error-1071-specified-key-was-too-long-max-key-length-is-767-bytes),

Creating new table...
Error creating new table: DBD::mysql::db do failed: Specified key was too long; max key length is 767 bytes [for Statement "CREATE TABLE `umami_prod`.`_membership_customers_new` (

It seems this was the cause

`uid` varchar(255) COLLATE utf8mb4_unicode_ci DEFAULT NULL,
UNIQUE KEY `index_membership_customers_on_uid_and_hotel_brand_id` (`uid`,`hotel_brand_id`)

so I want to resize the columns or change its character set, but whatever I got to do, it failed because pt-online-schema-change try to create a new table first, then it failed because of this index length issue in the beginning. I couldn't change anything

So my question is

  1. How does the current table support this utfm8 varchar(255), How does it possible?
UNIQUE KEY `index_membership_customers_on_uid_and_hotel_brand_id` (`uid`,`hotel_brand_id`)
  1. Maybe there are table settings I missed for pt-online-schema-change
  2. Anything I couldn't do, next, it is a 4M rows size table, and since pt-online-schema-change couldn't work because of the above issue, my only option is alter, to lock whole table?

Thanks for your reply, any hint might help, thanks

1 Answer 1


Can you live with 191 instead of 225? If not, your 5 options (including that one) are here:


  • Ya, I am ok 191 instead of 225, I couldn't, because the current problem is, that it would fail when executing pt-online-schema-change, so it seems I need to ask for maintenance to lock the table. Jun 27, 2022 at 2:03

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