Replication lag monitoring in Redis - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is replication lag in Redis?

Replication lag is the delay between when data is written on the master and when it is updated on the replica.

beginner

Which Redis command helps check the replication lag?

The INFO REPLICATION command shows replication details including the lag time.

intermediate

What does the master_repl_offset field represent in Redis replication info?

It shows the current replication offset of the master, indicating how much data has been sent to replicas.

intermediate

How can you estimate replication lag using offsets in Redis?

By comparing the master's master_repl_offset with the replica's slave_repl_offset, the difference shows lag in bytes.

beginner

Why is monitoring replication lag important in Redis?

Because high lag means replicas have outdated data, which can cause stale reads and affect application performance.

Which Redis command provides replication status including lag information?

A INFO REPLICATION

B MONITOR

C CLIENT LIST

D CONFIG GET

The INFO REPLICATION command shows replication details such as offsets and lag.

What does a large difference between master_repl_offset and slave_repl_offset indicate?

A Fast replication

B Low memory usage

C High replication lag

D Disconnected replica

A large difference means the replica is behind the master, causing lag.

If replication lag is high, what problem might occur?

A Replicas serve outdated data

B Master crashes

C Data loss on master

D Faster writes

High lag means replicas have stale data, which can cause outdated reads.

Which metric is NOT directly related to replication lag in Redis INFO REPLICATION output?

A master_repl_offset

B connected_clients

C slave_repl_offset

D master_link_status

connected_clients shows client connections, not replication lag.

How often should you monitor replication lag in a production Redis setup?

A Once a month

B Never

C Only after failures

D Continuously or frequently

Continuous monitoring helps catch lag early and maintain data freshness.

Explain how to check replication lag in Redis using command line tools.

Look at replication offsets in INFO REPLICATION output.

Why is it important to monitor replication lag in Redis and what issues can arise if lag is ignored?

Think about how delayed data affects users.