Maxmemory setting in Redis - Step-by-Step Execution

Concept Flow - Maxmemory setting

Start Redis Server

↓

Check maxmemory config

↓

Is maxmemory set?

No→Use unlimited memory

Yes↓

Limit memory usage to maxmemory

↓

When memory usage > maxmemory

↓

Apply eviction policy

↓

Free memory

↓

Continue running

Redis starts and checks if maxmemory is set. If yes, it limits memory usage and applies eviction when needed.

Execution Sample

Redis

CONFIG SET maxmemory 100mb
INFO memory
-- simulate memory usage --
-- memory > 100mb triggers eviction --

Set maxmemory to 100mb and observe memory usage and eviction when limit exceeded.

Execution Table

Step	Action	Memory Usage	maxmemory Setting	Eviction Triggered	Result
1	Start Redis server	0mb	Not set	No	Server runs with unlimited memory
2	Set maxmemory to 100mb	0mb	100mb	No	Memory limit applied
3	Memory usage grows to 80mb	80mb	100mb	No	No eviction needed
4	Memory usage grows to 105mb	105mb	100mb	Yes	Eviction policy activated
5	Eviction frees 20mb	85mb	100mb	No	Memory usage below limit
6	Memory usage stable at 85mb	85mb	100mb	No	Server continues running

💡 Memory usage is controlled by maxmemory; eviction triggers when usage exceeds limit.

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	After Step 5	Final
Memory Usage	0mb	0mb	80mb	105mb	85mb	85mb
maxmemory	Not set	100mb	100mb	100mb	100mb	100mb
Eviction Triggered	No	No	No	Yes	No	No

Key Moments - 3 Insights

Why does Redis start without any memory limit if maxmemory is not set?

As shown in execution_table row 1, if maxmemory is not set, Redis uses unlimited memory by default.

When exactly does Redis trigger eviction?

Eviction triggers when memory usage exceeds maxmemory, as seen in execution_table row 4 where usage is 105mb > 100mb.

Does eviction reduce memory usage below maxmemory immediately?

Yes, eviction frees memory to bring usage below maxmemory, shown in row 5 where usage drops from 105mb to 85mb.

Visual Quiz - 3 Questions

Look at the execution_table, what is the maxmemory setting after step 2?

A Not set

B 100mb

C 0mb

D Unlimited

💡 Hint

Check the 'maxmemory Setting' column at step 2 in the execution_table.

At which step does eviction get triggered according to the execution_table?

A Step 5

B Step 3

C Step 4

D Step 6

💡 Hint

Look at the 'Eviction Triggered' column to find when it changes to 'Yes'.

If maxmemory was set to 200mb instead of 100mb, what would happen at step 4?

A Memory usage would be below maxmemory, no eviction

B Eviction would trigger

C Redis would crash

D Memory usage would reset to 0

💡 Hint

Compare memory usage at step 4 (105mb) with a hypothetical maxmemory of 200mb.

Concept Snapshot

Maxmemory setting limits Redis memory use.
If memory usage exceeds maxmemory, eviction frees memory.
Without maxmemory, Redis uses unlimited memory.
Set maxmemory with CONFIG SET maxmemory <bytes>.
Eviction policy controls which keys to remove.
Helps prevent Redis from using too much RAM.

Full Transcript

Redis starts and checks if maxmemory is set. If not set, Redis uses unlimited memory. When maxmemory is set, Redis limits memory usage to that value. If memory usage grows beyond maxmemory, Redis triggers eviction to free memory. Eviction reduces memory usage below the limit so Redis can continue running smoothly. This process repeats as memory usage changes. Setting maxmemory helps control Redis memory consumption and avoid crashes.