How to make multiple writes in a transaction

Prerequisites

• Install etcd and etcdctl

Transactions

txn to process all the requests in one transaction:

etcdctl txn --help

Transactions in etcd allow you to execute multiple operations atomically, ensuring that either all operations are applied or none are. This is crucial for maintaining data consistency when performing related updates.

Example

Let’s consider a scenario where you want to update a user’s email and phone number in a single transaction. This ensures that both updates are applied together.

1. Set up initial data: First, create a user with some initial data.

   etcdctl put /users/12345/email "old.address@johndoe.com"
   etcdctl put /users/12345/phone "123-456-7890"
   

2. Perform a transaction: Update the user’s email and phone number in a single transaction.

   etcdctl txn --interactive
   
   compares:
   value("/users/12345/email") = "old.address@johndoe.com"
   
   success requests (get, put, delete):
   put /users/12345/email "new.address@johndoe.com"
   put /users/12345/phone "098-765-4321"
   
   failure requests (get, put, delete):
   get /users/12345/email
   

   • Compare: Check if the current email is “old.address@johndoe.com”. This ensures the transaction only proceeds if the data is as expected.
   • Success: If the comparison is true, update both the email and phone number.
   • Failure: If the comparison fails, retrieve the current email to understand why the transaction didn’t proceed.

Important considerations

• Atomicity: The transaction ensures that both the email and phone number are updated together. If the initial condition (comparison) is not met, neither update is applied.
• Consistency: Using transactions maintains data consistency, especially when dealing with multiple related updates.
• Avoid multiple puts on the same key: Do not put multiple values for the same key within a single transaction, as this can lead to unexpected results. Each key should be updated only once per transaction.