MULTI command to start in Redis - Step-by-Step Execution

Concept Flow - MULTI command to start

Client sends MULTI

↓

Server replies +OK

↓

Client queues commands

↓

Client sends EXEC

↓

Server executes all queued commands

↓

Server returns all results as array

The MULTI command starts a transaction by telling Redis to queue commands. Later, EXEC runs all queued commands atomically.

Execution Sample

Redis

MULTI
SET key1 value1
INCR counter
EXEC

Starts a transaction, queues SET and INCR commands, then executes them all together.

Execution Table

Step	Client Command	Server Response	State/Action
1	MULTI	+OK	Transaction mode started, commands will be queued
2	SET key1 value1	+QUEUED	Command queued, not executed yet
3	INCR counter	+QUEUED	Command queued, not executed yet
4	EXEC	*2	All queued commands executed atomically, results returned

💡 EXEC runs all queued commands and ends the transaction mode

Variable Tracker

Variable	Start	After 1	After 2	After 3	Final
transaction_mode	false	true	true	true	false
command_queue	empty	['SET key1 value1']	['SET key1 value1', 'INCR counter']	['SET key1 value1', 'INCR counter']	empty

Key Moments - 2 Insights

Why does the server reply +QUEUED instead of the actual command result after SET?

Because after MULTI, commands are only queued, not executed immediately. The actual results come after EXEC, as shown in execution_table row 2.

What happens if EXEC is not sent after MULTI?

Commands remain queued and are not executed. The transaction stays open, so no changes happen until EXEC or DISCARD is sent.

Visual Quiz - 3 Questions

Look at the execution table, what is the server response when the client sends INCR counter?

A +QUEUED

B *1

C +OK

D -ERROR

💡 Hint

Check execution_table row 3 under Server Response

At which step does the transaction mode end?

A After MULTI

B After SET command

C After EXEC

D After INCR command

💡 Hint

Look at execution_table row 4 and variable_tracker transaction_mode changes

If the client sends EXEC immediately after MULTI without any commands queued, what will happen?

A Server returns an error

B Server returns an empty array

C Server executes last command twice

D Server ignores EXEC

💡 Hint

Recall that EXEC runs all queued commands; if none queued, result is empty array

Concept Snapshot

MULTI starts a transaction in Redis.
Commands after MULTI are queued, not run.
Server replies +QUEUED for each queued command.
EXEC runs all queued commands atomically.
Transaction mode ends after EXEC or DISCARD.

Full Transcript

The MULTI command in Redis starts a transaction mode. When a client sends MULTI, the server replies with +OK and enters transaction mode. Commands sent after MULTI are not executed immediately but queued, with the server replying +QUEUED for each. When the client sends EXEC, Redis executes all queued commands atomically and returns their results as an array. The transaction mode ends after EXEC. If EXEC is not sent, commands remain queued and unexecuted. This ensures multiple commands run together safely.