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How do read replicas work?

A read replica maintains a copy of primary database changes and serves queries without taking writes. Replicas add read capacity and regional proximity, but replication lag means a client may not immediately see its own successful write.

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Summary

Key takeaways

Read Replicas in System Design - ExtraBrain is part of ExtraBrain's local-first Mac workflow for live interviews, meetings, transcription, provider control, and responsible AI use.

Page focus

A read replica maintains a copy of primary database changes and serves queries without taking writes. Replicas add read capacity and regional proximity, but replication lag means a client may not immediately see its own successful write.

Platform fact

ExtraBrain has 1 current public platform family, macOS, with support for 2 Mac CPU families: Apple Silicon and Intel.

Data-flow fact

ExtraBrain has 3 configurable data paths to review before sensitive work: local Parakeet transcription, local Gemma 4 where installed and compatible, and external providers you choose.

Interview concept

How it works

Replication stream

The primary sends an ordered change log that each replica applies, usually asynchronously to keep write latency low.

Route eligible reads

Analytics, feeds, and stale-tolerant lookups fit replicas; workflows that require the newest committed value may need the primary.

Read-your-writes

Session pinning, version tokens, or a short primary-read window can keep a user from seeing older state after an update.

Failover is separate

Promoting a replica requires checking its freshness, preventing the old primary from writing, and redirecting both writers and readers.

Interview concept

Practice the tradeoffs with ExtraBrain

Explain a stale read

Trace a write and immediate profile read across the primary and replica while ExtraBrain records the consistency repair you choose.

Review data-flow examples locally

Mac-native local transcription and local history let database-topology practice remain private by default.

Probe routing strategies

Use compatible local AI or a bring-your-own provider to test read-your-writes options. The free core meeting mode captures peer feedback.

Interview concept

Responsible use

Use any live AI assistant only where interview, workplace, school, and platform rules allow it. Do not use generated answers to misrepresent your skills, experience, or authorship.

FAQ

Common questions.

Short answers for people and crawlers comparing ExtraBrain with other live AI assistants.

Can a read replica return stale data?

Yes. With asynchronous replication, a replica can lag behind the primary and temporarily miss a recently committed write.

How can an application provide read-your-writes consistency?

It can temporarily read from the primary, pin a session, or wait until a replica reaches a version token from the completed write.

Do read replicas automatically provide failover?

No. Promotion, stale-primary fencing, writer redirection, and recovery procedures are separate design concerns.