Read-only replicas in Redis - Step-by-Step Execution

Concept Flow - Read-only replicas

Primary Redis Server

↓

Replicate Data to Read-only Replica

↓

Client Sends Read Request

↓

Read-only Replica Serves Data

↓

Client Receives Data

Data is copied from the primary Redis server to read-only replicas. Clients send read requests to replicas to reduce load on primary.

Execution Sample

Redis

1. PRIMARY SET key "value"
2. REPLICA syncs data
3. CLIENT GET key (read from replica)
4. REPLICA returns "value"

Shows how a write to primary is replicated and then read from a read-only replica.

Execution Table

Step	Action	Source	Target	Result
1	Write key 'key' with 'value'	Client	Primary	Primary stores key='value'
2	Replicate data	Primary	Replica	Replica copies key='value'
3	Client requests GET key	Client	Replica	Replica receives GET request
4	Replica returns value	Replica	Client	Client receives 'value'
5	Client tries to write on replica	Client	Replica	Replica rejects write (read-only)

💡 Replica rejects writes; only reads allowed on replicas

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 4	Final
Primary key	null	"value"	"value"	"value"	"value"
Replica key	null	null	"value"	"value"	"value"
Client read result	null	null	null	"value"	"value"

Key Moments - 2 Insights

Why can't the client write data directly to the read-only replica?

Because replicas are set to reject write commands to keep data consistent with the primary, as shown in step 5 of the execution_table.

How does the replica get updated data from the primary?

The primary server continuously replicates data changes to the replica, as shown in step 2 of the execution_table.

Visual Quiz - 3 Questions

Look at the execution_table, what does the replica return to the client at step 4?

A null

B "value"

C Error

D "key"

💡 Hint

Check the 'Result' column in step 4 of the execution_table.

At which step does the replica copy data from the primary?

A Step 1

B Step 3

C Step 2

D Step 5

💡 Hint

Look for the replication action in the execution_table.

If the client tries to write to the replica, what happens according to the execution_table?

A Replica rejects write (read-only)

B Replica forwards write to primary

C Replica accepts and stores data

D Client write is ignored silently

💡 Hint

See step 5 in the execution_table for write attempts on replica.

Concept Snapshot

Read-only replicas in Redis copy data from the primary server.
Clients send read requests to replicas to reduce load.
Replicas reject write commands to keep data consistent.
Writes go only to the primary server.
Replicas serve fast reads and improve scalability.

Full Transcript

In Redis, a primary server handles all writes. It copies data to read-only replicas. Clients send read requests to replicas to reduce load on the primary. Replicas reject write commands to keep data consistent. This setup improves read scalability and availability.