# How to change character set/collation on one column in a very large table

**URL:** <https://forums.percona.com/t/how-to-change-character-set-collation-on-one-column-in-a-very-large-table/36632>\
**Category:** Percona Toolkit\
**Created:** [February 10, 2025, 5:18pm UTC](https://forums.percona.com/t/how-to-change-character-set-collation-on-one-column-in-a-very-large-table/36632 "2025-02-10T17:18:02Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![eric.peterson](https://avatars.discourse-cdn.com/v4/letter/e/77aa72/32.png) [@eric.peterson](https://forums.percona.com/u/eric.peterson)\
**Post date:** [February 10, 2025, 5:18pm UTC](https://forums.percona.com/t/how-to-change-character-set-collation-on-one-column-in-a-very-large-table/36632/1 "2025-02-10T17:18:02Z")

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I do not want to run the following in production. Take forever while locking the table.

ALTER TABLE \<2.5B row table\>  
MODIFY COLUMN TEXT CHARACTER SET utf8mb4 COLLATE utf8mb4\_0900\_ai\_ci;

> SELECT @@aurora\_version a, VERSION() v;  
> ±-------±-------+  
> | a | v |  
> ±-------±-------+  
> | 3.05.2 | 8.0.32 |  
> ±-------±-------+

I’ve seen examples of changing everything, but I just want to do one column on one table. Is this doable? Do you have some guidance?

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**Author:** ![eric.peterson](https://avatars.discourse-cdn.com/v4/letter/e/77aa72/32.png) [@eric.peterson](https://forums.percona.com/u/eric.peterson)\
**Post date:** [February 10, 2025, 7:28pm UTC](https://forums.percona.com/t/how-to-change-character-set-collation-on-one-column-in-a-very-large-table/36632/2 "2025-02-10T19:28:46Z")

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Here is what I came up with. for a very large table, how will this impact production? what sort of locks might I expect (if any)?

I’ll try to make a copy of the table and run this to see what the timing is. But I’m concerned that the switchover might be a problem. If the ALTER takes more than 4 hours, then the outage window is closed and there will be user traffic on this busy table.

pt-online-schema-change   
–host 127.0.0.1   
–port 3366   
–user root   
–password xxx   
–no-version-check   
–execute   
–sleep 0.1   
–alter-foreign-keys-method drop\_swap   
–preserve-triggers   
–statistics   
–analyze-before-swap   
–alter “MODIFY COLUMN |column| TEXT CHARACTER SET utf8mb4 COLLATE utf8mb4\_0900\_ai\_ci”   
D=|schema|,t=|table|

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<div class="post-metadata">

**Author:** ![matthewb](https://sea1.discourse-cdn.com/flex019/user_avatar/forums.percona.com/matthewb/32/34_2.png) [@matthewb](https://forums.percona.com/u/matthewb)\
**Post date:** [February 11, 2025, 1:47pm UTC](https://forums.percona.com/t/how-to-change-character-set-collation-on-one-column-in-a-very-large-table/36632/3 "2025-02-11T13:47:02Z")

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Hey @eric.peterson,  
Your ptosc command looks good. Since you are using Aurora, I would recommend using their blue/greeen deployment system. Create the B/G, then run ptosc against the non-active side. Once finished, do a B/G swap. I don’t recommend changing just 1 column. Change the entire table since B/G won’t impact main systems, even if it takes more than 4 hours.