Cache-aside pattern in Redis - Step-by-Step Execution

Concept Flow - Cache-aside pattern

Request data

↓

Check cache

↓

Return

↓

Store in cache

↓

Return

The cache-aside pattern first checks the cache for data. If found (hit), it returns it. If not (miss), it fetches from the database, stores it in cache, then returns it.

Execution Sample

Redis

1. Check cache for key 'user:1'
2. If found, return cached data
3. Else, query DB for user 1
4. Store DB result in cache
5. Return data

This simulates a cache-aside pattern fetching user data by first checking Redis cache, then DB if needed.

Execution Table

Step	Action	Cache Check Result	DB Query	Cache Update	Return Value
1	Check cache for 'user:1'	Miss	No	No	No
2	Query DB for 'user:1'	N/A	Yes	No	No
3	Store DB result in cache	N/A	N/A	Yes	No
4	Return data to caller	N/A	N/A	N/A	User data from DB
5	Next request: Check cache for 'user:1'	Hit	No	No	User data from cache

💡 Execution stops after returning data; subsequent requests hit cache directly.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	After Step 5
cache['user:1']	empty	empty	empty	user data	user data	user data
db_result	none	none	user data	user data	user data	user data
return_value	none	none	none	none	user data	user data

Key Moments - 3 Insights

Why do we check the cache before querying the database?

Checking the cache first (Step 1) avoids unnecessary database queries, improving speed and reducing load, as shown in the execution_table where a cache hit skips DB query.

What happens when the cache misses the data?

On a cache miss (Step 1), the system queries the database (Step 2), then stores the result in cache (Step 3) before returning it (Step 4), ensuring future requests hit the cache.

Why do subsequent requests return data from cache?

After storing data in cache (Step 3), the cache holds the data for future requests, so the next check (Step 5) hits cache and returns data immediately without DB access.

Visual Quiz - 3 Questions

Look at the execution_table, what is the cache check result at Step 5?

A Hit

B Miss

C Empty

D Error

💡 Hint

Refer to the 'Cache Check Result' column at Step 5 in the execution_table.

At which step does the database get queried?

A Step 1

B Step 2

C Step 3

D Step 5

💡 Hint

Check the 'DB Query' column in the execution_table to find when it is 'Yes'.

If the cache already has the data, which steps are skipped?

A Steps 3 and 5

B Steps 1 and 4

C Steps 2 and 3

D Steps 1 and 2

💡 Hint

Look at the execution_table rows where cache check is 'Hit' and see which actions are 'No'.

Concept Snapshot

Cache-aside pattern:
1. Check cache for data.
2. If hit, return cached data.
3. If miss, query DB.
4. Store DB result in cache.
5. Return data.
Improves performance by reducing DB load.

Full Transcript

The cache-aside pattern works by first checking the cache for requested data. If the data is found (cache hit), it returns immediately, avoiding a database query. If the data is not found (cache miss), the system queries the database, stores the result in the cache for future use, and then returns the data. This pattern helps improve performance by reducing database load and speeding up data retrieval. The execution table shows each step: checking cache, querying DB if needed, updating cache, and returning data. Variables like cache content and return values change accordingly. Key moments include understanding why cache is checked first, what happens on a miss, and why subsequent requests hit the cache. The visual quiz tests understanding of these steps and their order.