Dissecting GitHub Outage: ID column reaching the max value 2147483647



1986 views Outage Dissections



On the 5th of May, 2020, GitHub experienced an outage because of this very reason. One of their shared table having an auto-incrementing ID column hits its max limit. Let’s see what could have been done in such a situation.

What’s the next value after MAX int?

GitHub used 4 bytes signed integer as their ID column, which means the value can go from -2147483648 to 2147483647. So, now when the ID column hits 2147483647 and tries to get the next value, it gets the same value again, i.e., 2147483647.

For MySQL, 2147483647 + 1 = 2147483647

So, when it tries to insert the row with ID 2147483647, it gets the Duplicate Key Error given that a row already exists with the same ID.

How to mitigate the issue?

A situation like this is extremely critical given that the database is not allowing us to insert any row in the table. This typically results in a major downtime of a few hours, and it depends on the amount of data in the table. There are a couple of ways to mitigate the issue.

Approach 1: Alter the table and increase the width of the column

Quickly fire the ALTER table and change the data type of the ID column to UNSIGNED INT or BIGINT. Depending on the data size, an ALTER query like this will take a few hours to a few days to execute. Hence this approach is suitable only when the table size is small.

Approach 2: Swap the table

The idea here is to create an empty table with the same schema but a larger ID range that starts from 2147483648. Then rename this new table to the old one and start accepting writes. Then slowly migrate the data from the old table to this new one. This approach can be used when you can live without the data for a few days.

Get warned before the storm

Although mitigation is great, it is better to place a monitoring system that raises an alert when the ID reaches 70% of its range. So, write a simple DB monitoring service that periodically checks this by firing a query on the database.


Arpit Bhayani

Arpit's Newsletter

CS newsletter for the curious engineers

❤️ by 17000+ readers

If you like what you read subscribe you can always subscribe to my newsletter and get the post delivered straight to your inbox. I write essays on various engineering topics and share it through my weekly newsletter.




Other essays that you might like


So, the outage is mitigated, now what?

500 views 24 likes 2022-07-08

Outages happen and in such a tense situation, the main priority is to get the system back up, but is that it? Is everyth...

Control an outage by localizing the failures

444 views 31 likes 2022-07-06

Outages are inevitable; but we should design our architecture such that if a component is down, it should not lead to a ...

Dissecting GitHub Outage - Multiple Leaders in Zookeeper Cluster

1059 views 58 likes 2022-07-01

Distributed Systems are prone to problems that seem very obscure. GitHub had an outage because a set of nodes in the Zoo...

GitHub Outage - How databases are managed in production

1165 views 81 likes 2022-06-29

So, how are databases managed in production? When the master goes down, how a replica is chosen and promoted to be the n...


Be a better engineer

A set of courses designed to make you a better engineer and excel at your career; no-fluff, pure engineering.


System Design Masterclass

A masterclass that helps you become great at designing scalable, fault-tolerant, and highly available systems.

Enrolled by 700+ learners

Details →

Designing Microservices

A free course to help you understand Microservices and their high-level patterns in depth.

Enrolled by 17+ learners

Details →

GitHub Outage Dissections

A free course to help you learn core engineering from outages that happened at GitHub.

Enrolled by 67+ learners

Details →

Hash Table Internals

A free course to help you learn core engineering from outages that happened at GitHub.

Enrolled by 25+ learners

Details →

BitTorrent Internals

A free course to help you understand the algorithms and strategies that power P2P networks and BitTorrent.

Enrolled by 42+ learners

Details →

Topics I talk about

Being a passionate engineer, I love to talk about a wide range of topics, but these are my personal favourites.




Arpit's Newsletter read by 17000+ engineers

🔥 Thrice a week, in your inbox, an essay about system design, distributed systems, microservices, programming languages internals, or a deep dive on some super-clever algorithm, or just a few tips on building highly scalable distributed systems.



  • v12.4.4
  • © Arpit Bhayani, 2022

Powered by this tech stack.