Combined RDB + AOF in Redis - Step-by-Step Execution

Concept Flow - Combined RDB + AOF

Start Redis Server

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Load RDB Snapshot

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Apply AOF Commands

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Data Fully Restored

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Serve Client Requests

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Periodically Save RDB Snapshot

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Append New Commands to AOF

↩Back to Serve Client Requests

Redis starts by loading the RDB snapshot, then replays AOF commands to restore the latest data, and continues serving clients while saving snapshots and appending commands.

Execution Sample

Redis

1. redis-server starts
2. Load RDB snapshot file
3. Replay AOF command log
4. Data restored
5. Serve clients
6. Save RDB periodically
7. Append new commands to AOF

This sequence shows how Redis restores data using RDB and AOF combined, then continues normal operation.

Execution Table

Step	Action	Data State	Result
1	Start Redis server	Empty	Server running, no data loaded
2	Load RDB snapshot	Partial data loaded	Data from last snapshot restored
3	Replay AOF commands	Data updated	Commands applied to reach latest state
4	Data fully restored	Complete data	Ready to serve clients
5	Serve client requests	Data changes	Clients can read/write data
6	Save RDB snapshot periodically	Snapshot updated	New snapshot saved on disk
7	Append new commands to AOF	AOF file grows	Commands logged for durability
8	Repeat serving clients	Data changes	Cycle continues
9	Exit	N/A	Server stopped or restarted

💡 Execution stops when the server shuts down or restarts.

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	After Step 5	After Step 6	After Step 7	Final
Data in memory	Empty	Partial from RDB	Updated with AOF	Complete	Changes with clients	Snapshot saved	Commands appended	Changes with clients
RDB snapshot file	Old snapshot	Loaded	Unchanged	Unchanged	Unchanged	New snapshot saved	Unchanged	Unchanged
AOF file	Old AOF	Unchanged	Replayed	Unchanged	Unchanged	Unchanged	Appended new commands	Unchanged

Key Moments - 3 Insights

Why does Redis load the RDB snapshot before replaying the AOF?

Loading the RDB snapshot quickly restores a recent full state, then replaying the AOF applies only the changes since that snapshot, making recovery faster (see execution_table steps 2 and 3).

What happens if the AOF file is missing or corrupted?

Redis can still load data from the RDB snapshot but will miss recent changes not saved in the snapshot, so data may be lost (refer to execution_table step 2 without step 3).

Why does Redis keep appending commands to the AOF after loading data?

Appending commands ensures all new changes are logged for durability, so if Redis restarts again, it can replay these commands to restore the latest state (see execution_table step 7).

Visual Quiz - 3 Questions

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

A Data updated with AOF commands

B Partial data loaded

C Empty

D Complete data ready to serve

💡 Hint

Check the 'Data State' column for step 3 in the execution_table.

At which step does Redis start serving client requests?

A Step 4

B Step 5

C Step 6

D Step 7

💡 Hint

Look for the action 'Serve client requests' in the execution_table.

If Redis did not save RDB snapshots periodically, which step would be missing?

A Step 2

B Step 3

C Step 6

D Step 7

💡 Hint

Check which step mentions saving RDB snapshots periodically in the execution_table.

Concept Snapshot

Combined RDB + AOF in Redis:
- On startup, load RDB snapshot (fast full data)
- Replay AOF commands (recent changes)
- Serve clients with full data
- Periodically save new RDB snapshots
- Append new commands to AOF for durability
- Combines speed (RDB) and safety (AOF)

Full Transcript

This visual execution shows how Redis uses both RDB snapshots and AOF command logs to restore data. First, Redis loads the RDB snapshot file to quickly restore a recent full state. Then it replays the AOF commands to apply all changes since the snapshot, reaching the latest data state. After data is fully restored, Redis serves client requests, allowing reads and writes. While running, Redis periodically saves new RDB snapshots to disk and appends new commands to the AOF file to ensure durability. This combination balances fast recovery and data safety. The execution table traces each step, showing data state changes and actions. The variable tracker follows memory data, RDB snapshot file, and AOF file states through the process. Key moments clarify why Redis loads RDB before AOF, what happens if AOF is missing, and why commands keep appending to AOF. The quiz tests understanding of data states and steps. This approach helps beginners see how Redis recovers and maintains data using combined persistence methods.