Interview › Databases & Caching
What is Redis replication, and how does a replica stay in sync?
Databases & Caching · Advanced level
Answer
Redis replication copies data from a primary to replicas through initial synchronization and ongoing write streams. It improves read scale and HA, but is usually asynchronous, so replicas can lag.
Technical explanation
Initial sync copies a snapshot or backlog; ongoing sync applies the primary write stream.
Replication lag can appear during high write volume, network issues, or slow replicas.
Replica reads can be stale, so strongly consistent reads should use the primary.
Hands-on example
Replication check:
INFO replication
Review role, connected_replicas, master_repl_offset, replica offsets, and link status.
Alert on sustained lag or broken replica links.
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