Intermediate LevelSystem Design & Architecture
How do you architect Database Read/Write Splitting with Sticky Replica routing?
❓ Interview Prompt: Explain Read/Write Splitting, asynchronous primary-to-replica replication lag, and Sticky Replica routing to prevent stale read glitches.
Architecting database read/write splitting routes 'INSERT/UPDATE' traffic to the Primary DB and 'SELECT' traffic to Read Replicas:
Replication Lag Glitch & Sticky Fix:
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Problem: User updates profile name $\rightarrow$ Redirects to profile page $\rightarrow$ Reads from replica before replication completes $\rightarrow$ User sees old profile name!
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Sticky Replica Routing: When a user writes data, flag their session to route ALL subsequent reads to the Primary DB for 5 seconds, guaranteeing they read their own writes!
Code Implementation Example
typescript
export async function handleProfileRead(req: Request, res: Response) {
const userWroteRecently = req.session.lastWriteTimestamp > Date.now() - 5000;
// Route to Primary DB if user wrote recently; otherwise use Read Replica!
const dbClient = userWroteRecently ? primaryDb : readReplicaDb;
const profile = await dbClient.user.findUnique({ where: { id: req.user.id } });
res.json(profile);
}💡Routing recent writers to Primary DB to prevent replication lag glitches.
🎯 Interview Key Takeaway
Use Sticky Replica routing to direct recent writers to the primary database, eliminating replication lag read glitches.
#System Design#Read Write Split#Replication Lag#Databases#Intermediate
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