Caching strategies in Supabase - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is caching in cloud infrastructure?

Caching is a way to store copies of data temporarily so that future requests for that data can be served faster without fetching from the original source every time.

beginner

Name a common caching strategy used to keep data fresh.

Time-to-Live (TTL) is a common caching strategy where cached data expires after a set time, forcing a refresh from the original source.

intermediate

What does 'cache invalidation' mean?

Cache invalidation means removing or updating cached data when it becomes outdated or incorrect, so users get the latest information.

advanced

Explain the difference between 'write-through' and 'write-back' caching.

Write-through caching updates the cache and the main storage at the same time, ensuring consistency. Write-back caching updates the cache first and writes to main storage later, improving speed but risking data loss if not handled carefully.

beginner

How can caching improve performance in Supabase applications?

Caching reduces the number of database calls by storing frequent query results temporarily, which speeds up response times and lowers server load.

What is the main purpose of caching in cloud apps?

A To permanently store all data

B To encrypt data for security

C To delete old data automatically

D To speed up data access by storing copies temporarily

Caching stores data copies temporarily to serve future requests faster.

Which caching strategy removes data after a set time?

A Time-to-Live (TTL)

B Write-through

C Write-back

D Cache warming

TTL sets an expiration time for cached data to keep it fresh.

What does cache invalidation do?

A Adds new data to cache

B Removes or updates outdated cached data

C Encrypts cached data

D Duplicates cached data

Cache invalidation ensures cached data stays accurate by removing or updating old data.

In write-through caching, when is data written to main storage?

A At the same time as cache update

B Only on cache miss

C Never

D Only after cache is full

Write-through updates both cache and main storage simultaneously.

How does caching help Supabase apps?

A By increasing database calls

B By slowing down response times

C By reducing database calls and speeding responses

D By deleting user data

Caching reduces database calls and speeds up app responses.

Describe three common caching strategies and how they help keep data fresh.

Think about how cached data stays accurate and when it gets updated or removed.

Explain why caching is important in cloud applications like Supabase and how it improves user experience.

Imagine waiting for a webpage to load with and without caching.

Practice

1. What is the main purpose of caching in Supabase applications?

easy

A. To store data temporarily and speed up data access

B. To permanently save all user data

C. To delete old data from the database

D. To encrypt data for security

Solution

1. Step 1: Understand caching basics

   Caching temporarily stores data to avoid repeated database calls.

2. Step 2: Identify caching purpose in Supabase

   It speeds up app performance by quickly providing stored data.

3. Final Answer:

   To store data temporarily and speed up data access -> Option A

4. Quick Check:

   Caching = Temporary storage for speed [OK]

Hint: Caching means temporary storage to speed up access [OK]

Common Mistakes:

• Thinking caching permanently saves data
• Confusing caching with encryption
• Believing caching deletes data

2. Which of the following is the correct way to set a cache TTL (time-to-live) in Supabase client code?

easy

A. cache.set('key', value, { ttl: 300 })

B. cache.set('key', value, ttl=300)

C. cache.set('key', value, timeout: 300)

D. cache.set('key', value, expire: 300)

Solution

1. Step 1: Review Supabase cache TTL syntax

   Supabase uses an options object with a ttl property to set time-to-live.

2. Step 2: Match correct syntax

   cache.set('key', value, { ttl: 300 }) uses { ttl: 300 } which is the correct way to specify TTL in seconds.

3. Final Answer:

   cache.set('key', value, { ttl: 300 }) -> Option A

4. Quick Check:

   TTL set with { ttl: seconds } object [OK]

Hint: TTL uses { ttl: seconds } object in cache.set [OK]

Common Mistakes:

• Using ttl=300 instead of { ttl: 300 }
• Using wrong property names like timeout or expire
• Passing TTL as a separate argument without object

3. Given this Supabase cache check code:

const cachedData = cache.get('user_123');
if (cachedData) {
  console.log('Cache hit:', cachedData);
} else {
  const data = await supabase.from('users').select('*').eq('id', 123);
  cache.set('user_123', data, { ttl: 600 });
  console.log('Cache miss, fetched:', data);
}

What will be logged if the cache already has data for 'user_123'?

medium

A. Cache miss, fetched: [new data]

B. Cache hit: [cached data]

C. Error: cache.get is not a function

D. No output

Solution

1. Step 1: Check cache.get return value

   If cache has data for 'user_123', cachedData is truthy.

2. Step 2: Follow code logic on cache hit

   Code logs 'Cache hit:' plus cachedData without fetching from database.

3. Final Answer:

   Cache hit: [cached data] -> Option B

4. Quick Check:

   Cache hit logs cached data [OK]

Hint: Cache hit means cachedData exists, logs cache hit [OK]

Common Mistakes:

• Assuming it fetches from database even if cache exists
• Confusing cache miss and hit outputs
• Expecting errors when cache is valid

4. You wrote this code to cache user data but it always fetches from the database:

const cached = cache.get('user_1');
if (!cached) {
  const data = await supabase.from('users').select('*').eq('id', 1);
  cache.set('user_1', data, { ttl: 300 });
}
console.log(cached);

What is the main issue causing the cache miss?

medium

A. TTL is too short to keep data

B. cache.get syntax is incorrect

C. You never update the cached variable after setting cache

D. Database query is wrong

Solution

1. Step 1: Analyze variable assignment

   Variable 'cached' is assigned once before cache.set, so it stays null.

2. Step 2: Understand cache update logic

   After setting cache, 'cached' is not updated to new data, so console.log shows null.

3. Final Answer:

   You never update the cached variable after setting cache -> Option C

4. Quick Check:

   cached variable must update after cache.set [OK]

Hint: Update cached variable after cache.set to avoid misses [OK]

Common Mistakes:

• Assuming cache.set updates cached variable automatically
• Blaming TTL without checking variable assignment
• Thinking cache.get syntax is wrong without error

5. You want to optimize a Supabase app by caching user profile data but ensure updates are reflected quickly. Which caching strategy is best?

hard

A. Cache data without TTL and manually clear cache daily

B. Use very long TTL (e.g., 24 hours) to minimize database calls

C. Never cache user profiles to avoid stale data

D. Use short TTL (e.g., 60 seconds) and refresh cache after updates

Solution

1. Step 1: Consider update frequency and freshness

   User profiles may change, so cache must refresh often to avoid stale data.

2. Step 2: Choose caching strategy balancing speed and freshness

   Short TTL with cache refresh after updates keeps data fresh and speeds access.

3. Final Answer:

   Use short TTL (e.g., 60 seconds) and refresh cache after updates -> Option D

4. Quick Check:

   Short TTL + refresh = fresh and fast cache [OK]

Hint: Short TTL plus refresh keeps cache fresh and fast [OK]

Common Mistakes:

• Using long TTL causing stale data
• Avoiding cache entirely losing speed benefits
• Not refreshing cache after updates