Database / Supabase basics Interview Questions

How does Supabase Realtime broadcast database changes to clients?

Supabase Realtime listens to Postgres's built-in logical replication stream (the same mechanism used for replication to standby servers) and converts row-level INSERT, UPDATE, and DELETE events into messages pushed over WebSockets to subscribed clients.

A client subscribes to a channel scoped to a table or even a specific filter, for example rows where room_id = 42, and receives a payload the moment a matching change commits. Realtime also supports two other channel types beyond database changes: Presence, for tracking which users are currently online in a shared space, and Broadcast, for sending arbitrary low-latency messages between clients (like cursor positions) without touching the database at all.

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What underlying Postgres mechanism does Realtime tap into for database change events? Cron jobs

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Logical replication

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Table backups

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Manual polling every second

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Which Realtime channel type is used to send messages like live cursor positions without writing to the database? Broadcast

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Presence

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Storage Events

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Postgres Changes

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More Related questions...

What is Supabase? What is the purpose of PostgreSQL within Supabase? What are the core services offered by Supabase? What is Supabase Authentication used for? What are the types of storage available in Supabase Storage? Define Row Level Security in Supabase? Describe the Supabase client library? What is the purpose of Supabase Edge Functions? List the API types Supabase auto-generates from your schema? How do you create a new Supabase project and connect to it? How does Supabase auto-generate REST APIs from a database schema? Why is Row Level Security important in a client-facing Supabase app? How does Supabase Realtime broadcast database changes to clients? What is the difference between the anon key and the service role key in Supabase? When should you use an Edge Function instead of a Postgres database function? How do you troubleshoot a valid query being blocked by Row Level Security? What is the difference between using Supabase Auth and rolling your own JWT-based authentication? How is data validated before insertion in a Supabase table? Why do we use database migrations in Supabase projects? What happens when a Postgres trigger fires on a table linked to Edge Function webhooks? Explain the execution flow of a request through Supabase's auto-generated API? Why doesn't Supabase recommend using the service_role key on the client? How can you optimize Postgres connection pooling for serverless Edge Functions? Explain the internal working of Row Level Security policy evaluation in Postgres? What is the difference between pgvector similarity search and hybrid search in Supabase? Which is better for real-time collaboration, Supabase Realtime or client-side polling, and why? How does Supabase handle connection pooling for high-concurrency workloads? Explain the lifecycle of a Supabase Auth session token? When would you choose self-hosting Supabase over the managed cloud offering? How do you optimize full-text search performance on a large Postgres table in Supabase?

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Database / Supabase basics Interview Questions

How does Supabase Realtime broadcast database changes to clients?

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