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28 August 2019

Switching id type from int to uuid in mysql

by Linus Probert

I ran into an issue the other day where a database I was using at work for a micro service wasn’t replication safe. The solution took some research so I thought I’d share it for others to be able to make use of it.

First the setup. Imagine that you’re running a microservice in a cluster (eg. kubernetes). Your service is running in 2 instances with two separate databases. There is replication enabled between the two databases to make sure that both databases reflect the same reality to your microservice.

Initially I set up my database table like this (MySQL):

create table information (
  id integer auto_increment,
  /* Additional irellevant columns */
  primary key (id)

A while later I was informed about issues that could appear during replication. Eg if two services create different entries in their respective database there is a risk that they auto_increment the same id on those separate entries. When the replication does happen between the databases this conflicting id will cause the replication to fail.

After reading up a bit on MySQL I discovered UUID(). I then decided that this was a better id to use for my table entries.

This is how I patched my database:

alter table information
    add column uuid varchar(36) default '' not null first;

update information
    set uuid = UUID();

alter table information
    drop primary key,
    drop column id,
    change uuid id varchar(36),
    add constraint primary key (id);

Since UUID() is documented to produce unique identifiers between tables, databases and servers this should be a safer solution when faced with replication setups.

If you don’t like storing a lot of VARCHAR(36) values in your database then you should be able to work out a solution similar to the below example.

create table information (
  id binary(16) not null,
  /* Additional irellevant columns */
  primary key (id)

/* On insert or read you can use the following utility functions */

I’ll leave it up to you how you’d want to work that out. Hope my solution for changing after the fact helps someone.

Br, Liq