KEYS pattern matching (avoid in production) in Redis - Step-by-Step Execution

Concept Flow - KEYS pattern matching (avoid in production)

Start

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Input pattern

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Scan all keys in Redis

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Match keys against pattern

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Return matched keys

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End

The KEYS command scans all keys in Redis and returns those matching the given pattern.

Execution Sample

Redis

KEYS user:*

# Returns all keys starting with 'user:'

This command finds all keys that start with 'user:' by matching the pattern.

Execution Table

Step	Action	Current Key	Pattern	Match Result	Output Keys
1	Start scanning keys		user:*		[]
2	Check key	user:1	user:*	Match	["user:1"]
3	Check key	user:2	user:*	Match	["user:1", "user:2"]
4	Check key	session:1	user:*	No Match	["user:1", "user:2"]
5	Check key	user:profile	user:*	Match	["user:1", "user:2", "user:profile"]
6	Check key	config	user:*	No Match	["user:1", "user:2", "user:profile"]
7	Finish scanning		user:*		["user:1", "user:2", "user:profile"]

💡 All keys scanned; matched keys returned.

Variable Tracker

Variable	Start	After 1	After 2	After 3	After 4	After 5	Final
Output Keys	[]	["user:1"]	["user:1", "user:2"]	["user:1", "user:2"]	["user:1", "user:2", "user:profile"]	["user:1", "user:2", "user:profile"]	["user:1", "user:2", "user:profile"]

Key Moments - 3 Insights

Why does KEYS scan all keys instead of using an index?

Because Redis stores keys in a simple dictionary without indexes for patterns, KEYS must check every key to find matches, as shown in execution_table rows 2-6.

Why is KEYS not recommended in production?

Because scanning all keys blocks Redis and slows down performance, especially with many keys, as the command checks each key one by one (see execution_table).

What does the pattern 'user:*' mean?

It means match any key starting with 'user:' followed by any characters, which is why keys like 'user:1' and 'user:profile' match (rows 2,3,5).

Visual Quiz - 3 Questions

Look at the execution table, what keys are matched after checking 'session:1'?

A ["user:1", "user:2"]

B ["user:1"]

C ["user:1", "user:2", "session:1"]

D []

💡 Hint

Check the Output Keys column at step 4 in the execution_table.

At which step does the command finish scanning all keys?

A Step 5

B Step 7

C Step 6

D Step 4

💡 Hint

Look for the 'Finish scanning' action in the execution_table.

If the pattern was '*:1', which key would match?

A user:profile

B user:1

C config

D session:1

💡 Hint

Consider keys ending with ':1' and check the pattern matching logic.

Concept Snapshot

KEYS pattern matching in Redis:
- Syntax: KEYS <pattern>
- Scans all keys to find matches
- Patterns use * as wildcard
- Not recommended in production due to blocking and performance
- Use SCAN for safer iteration

Full Transcript

The Redis KEYS command takes a pattern and scans all keys in the database to find those that match. It checks each key one by one against the pattern, collecting matches. For example, KEYS user:* returns all keys starting with 'user:'. This command can block Redis if many keys exist, so it is advised to avoid using KEYS in production environments. Instead, use SCAN for incremental iteration. The pattern supports wildcards like '*', matching any characters. The execution table shows step-by-step how keys are checked and matched, and the output keys grow as matches are found.