Synchronization process in Redis - Step-by-Step Execution

Concept Flow - Synchronization process

Client connects to Redis server

↓

Server sends RDB snapshot

↓

Client loads RDB snapshot

↓

Server sends command stream

↓

Client applies commands to sync data

↓

Synchronization complete

↓

Client ready

The Redis synchronization process starts with the client connecting, receiving a snapshot, loading it, then applying live commands until fully synced.

Execution Sample

Redis

CLIENT CONNECT
SERVER SENDS RDB
CLIENT LOADS RDB
SERVER SENDS COMMANDS
CLIENT APPLIES COMMANDS
SYNC COMPLETE

Shows the step-by-step flow of Redis synchronization from connection to completion.

Execution Table

Step	Action	Data Sent/Received	Client State	Server State
1	Client connects to server	Connection request	Connecting	Waiting for client
2	Server sends RDB snapshot	RDB snapshot data	Receiving snapshot	Sending snapshot
3	Client loads RDB snapshot	None	Loading data	Snapshot sent
4	Server sends command stream	Commands since snapshot	Applying commands	Sending commands
5	Client applies commands	None	Syncing data	Streaming commands
6	Synchronization complete	None	Ready	Sync complete

💡 Synchronization ends when client has fully loaded snapshot and applied all commands.

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 5	Final
Client State	Disconnected	Receiving snapshot	Loading data	Syncing data	Ready
Server State	Idle	Sending snapshot	Snapshot sent	Streaming commands	Sync complete

Key Moments - 2 Insights

Why does the client first load an RDB snapshot before applying commands?

The client loads the RDB snapshot to get a full copy of the database at a point in time, then applies commands to catch up with changes after that snapshot (see execution_table rows 2 and 4).

What happens if the client misses commands after loading the snapshot?

If commands are missed, the client data will be out of sync. The command stream ensures the client applies all changes after the snapshot to stay consistent (see execution_table rows 4 and 5).

Visual Quiz - 3 Questions

Look at the execution_table, what is the client state after step 3?

A Loading data

B Ready

C Syncing data

D Disconnected

💡 Hint

Check the 'Client State' column at step 3 in execution_table.

At which step does the server start sending commands to the client?

A Step 2

B Step 4

C Step 5

D Step 6

💡 Hint

Look at the 'Action' and 'Data Sent/Received' columns in execution_table.

If the client never applies commands after loading the snapshot, what will be the final client state?

A Ready

B Syncing data

C Loading data

D Disconnected

💡 Hint

Refer to variable_tracker for client state changes after loading snapshot and applying commands.

Concept Snapshot

Redis Synchronization Process:
1. Client connects to server.
2. Server sends RDB snapshot (full data).
3. Client loads snapshot.
4. Server streams commands since snapshot.
5. Client applies commands to sync.
6. Client ready when fully synced.

Full Transcript

The Redis synchronization process begins when the client connects to the Redis server. The server sends a full snapshot of the database called an RDB snapshot. The client loads this snapshot to get a complete copy of the data at that moment. After loading, the server sends a stream of commands that happened after the snapshot. The client applies these commands to update its data and stay in sync. When all commands are applied, synchronization is complete and the client is ready to use. This process ensures the client has an accurate and up-to-date copy of the Redis data.