Have you ever observed your app updating one server, and then it takes a few seconds to display the same thing on another server? That time delay is called replication lag. I encountered this issue after clients told me their data "wasn't updating." Their backup database was slow to replicate changed records from the primary database.
Let us dig into why this happens and what steps you can take to help mitigate it.
For services that are deployed using cloud applications, having replica databases helps with backup and increased incoming traffic load balancing so that users will have higher availability. A lagging back up could cause a faulty user experience, users seeing stale records, or records that don't match.
Think of it this way, you might text a friend immediately and after sending the text, their chat app will not display the text until it gets caught up in their chat app feeds, that is replication lag.
• Network delay - Data still needs to move between cloud regions, and the farther the servers are the more lag.
• Too many updates - Your main database may be hit with many write requests, and that means replicas cannot keep up.
• Slow storage - If your replica is on a slower disk the changes take longer to be saved.
• Replication type - Some replication techniques (called asynchronous replication) the main database does not have to wait for confirmation from the replica to move on. This means the main database will continue to get updates, forming a lag between replicas.
Think of it like downloading a file, over slow Wi-Fi. Your replica is trying to “download” the updates, but falls behind the main database almost every time.
1. Improve queries and indexing – When your database is efficient, it can do more to handle writes.
2. Utilize faster disks/ storage – Utilizing SSDs or a higher tier of cloud storage can make an incredible difference.
3. Keep an eye on the lag – You can use tools like AWS CloudWatch, Datadog, or visit your cloud dashboard to catch delays early.
4. Use semi-synchronous replication – It's a little slow but keeps your replicas more current.
5. Keep replicas close – Hosting your replica in the same region, even the same availability zone will lower the impact of network delay.
Even small changes can make a big difference.
So, the next time you think your cloud database is slow, check the lag first. You may realize that's actually the problem.
Because in the cloud, it's not just about how fast something can be done. Many times it is about keeping everything in-sync.
Let us dig into why this happens and what steps you can take to help mitigate it.
What Is Replication Lag?
Replication lag is when records change in the primary (main) database, and then it takes time to update those records in the backup (copy) database.For services that are deployed using cloud applications, having replica databases helps with backup and increased incoming traffic load balancing so that users will have higher availability. A lagging back up could cause a faulty user experience, users seeing stale records, or records that don't match.
Think of it this way, you might text a friend immediately and after sending the text, their chat app will not display the text until it gets caught up in their chat app feeds, that is replication lag.
Reasons For Replication Lag
You may wonder why, with cloud systems so fast, there can be lag? Below are a few common reasons that can cause replication to lag:• Network delay - Data still needs to move between cloud regions, and the farther the servers are the more lag.
• Too many updates - Your main database may be hit with many write requests, and that means replicas cannot keep up.
• Slow storage - If your replica is on a slower disk the changes take longer to be saved.
• Replication type - Some replication techniques (called asynchronous replication) the main database does not have to wait for confirmation from the replica to move on. This means the main database will continue to get updates, forming a lag between replicas.
Think of it like downloading a file, over slow Wi-Fi. Your replica is trying to “download” the updates, but falls behind the main database almost every time.
How to Resolve Replication Lag
The great news is you can get on top of it by taking a few insightful actions:1. Improve queries and indexing – When your database is efficient, it can do more to handle writes.
2. Utilize faster disks/ storage – Utilizing SSDs or a higher tier of cloud storage can make an incredible difference.
3. Keep an eye on the lag – You can use tools like AWS CloudWatch, Datadog, or visit your cloud dashboard to catch delays early.
4. Use semi-synchronous replication – It's a little slow but keeps your replicas more current.
5. Keep replicas close – Hosting your replica in the same region, even the same availability zone will lower the impact of network delay.
Even small changes can make a big difference.
Conclusion
Replication lag can break user experience - orders can go missing, or the data looks stale. But knowing what can cause this lag means, fixing it is fairly low lift.So, the next time you think your cloud database is slow, check the lag first. You may realize that's actually the problem.
Because in the cloud, it's not just about how fast something can be done. Many times it is about keeping everything in-sync.