Lua vs transactions comparison in Redis - Visual Side-by-Side Comparison

Concept Flow - Lua vs transactions comparison

Start Client Command

↓

Choose: Use Lua Script?

No→Use MULTI/EXEC Transaction

↓

Queue Commands

↓

Run Lua Script Atomically

↓

EXEC Executes All

↓

Atomic Execution Complete

↓

Return Result to Client

This flow shows how Redis handles atomic operations either by running a Lua script atomically or by queuing commands in a MULTI/EXEC transaction.

Execution Sample

Redis

MULTI
SET key1 100
INCR key1
EXEC

This Redis transaction queues commands and executes them atomically with EXEC.

Execution Table

Step	Action	Command	State Before	State After	Result
1	Start Transaction	MULTI	key1 does not exist	Transaction started	OK
2	Queue Command	SET key1 100	Transaction started	SET queued	QUEUED
3	Queue Command	INCR key1	SET queued	INCR queued	QUEUED
4	Execute Transaction	EXEC	Commands queued	key1=101	["OK", 101]
5	End	N/A	Transaction executed	No active transaction	N/A

💡 EXEC runs all queued commands atomically, then transaction ends.

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	Final
key1	NULL	NULL	NULL	101	101
Transaction State	None	Started	Started	Executed	None

Key Moments - 2 Insights

Why does the key1 value only change after EXEC?

Commands are only queued during MULTI; actual changes happen atomically when EXEC runs, as shown in execution_table step 4.

How is Lua script execution different from MULTI/EXEC?

Lua scripts run all commands atomically in one go without queuing, unlike MULTI/EXEC which queues commands before execution.

Visual Quiz - 3 Questions

Look at the execution_table at step 3, what is the state of the transaction?

A Transaction executed

B No active transaction

C Transaction started and commands queued

D Transaction aborted

💡 Hint

Refer to execution_table row 3, 'State After' column shows 'INCR queued'.

At which step does key1 get its new value?

A Step 2

B Step 4

C Step 3

D Step 5

💡 Hint

Check execution_table step 4, 'State After' shows 'key1=101'.

If we replace MULTI/EXEC with a Lua script doing the same commands, what changes?

A Commands execute atomically without queuing

B Commands are queued before execution

C Commands execute one by one with delays

D Commands cannot modify keys

💡 Hint

See key_moments explanation about Lua scripts running atomically in one go.

Concept Snapshot

Redis MULTI/EXEC queues commands and runs them atomically on EXEC.
Lua scripts run all commands atomically in one execution without queuing.
MULTI/EXEC is multi-step; Lua script is single-step atomic.
Both ensure atomicity but differ in execution style and complexity.
Use Lua for complex logic; MULTI/EXEC for simple grouped commands.

Full Transcript

This visual execution compares Redis Lua scripts and MULTI/EXEC transactions. MULTI starts a transaction, queues commands like SET and INCR, then EXEC runs all queued commands atomically, updating key1 from NULL to 101. Lua scripts run all commands atomically in one step without queuing. The key difference is that MULTI/EXEC separates queuing and execution, while Lua scripts execute all logic in one atomic call. This ensures atomicity in both but with different workflows. Beginners often confuse when changes happen in MULTI/EXEC; changes only apply at EXEC. Lua scripts simplify atomic execution by running all commands together. This comparison helps understand when to use each method in Redis.