--- title: "How do you decide what data should be cached and for how long?" description: "How do you decide what data should be cached and for how long?" author: "Anubhav Sharma" published: 2025-04-02 updated: 2025-04-02 canonical: https://www.mindstick.com/interview/34024/how-do-you-decide-what-data-should-be-cached-and-for-how-long category: "cache" tags: ["cache", "programming help"] reading_time: 6 minutes --- # How do you decide what data should be cached and for how long? #### How to Decide What Data to Cache and for How Long? Caching is a trade-off between **freshness** and **performance**. To decide what data to cache and for how long, consider the following factors: #### 1. What Data Should Be Cached? ## Good Candidates for Caching | Data Type | Reason for Caching | | --- | --- | | **Frequently accessed data** | Avoid redundant database or API calls (e.g., top articles, user profile). | | **Expensive computations** | Save CPU time (e.g., complex reports, aggregated statistics). | | **Static or rarely changing data** | No need to fetch frequently (e.g., product categories, country lists). | | **Third-party API responses** | Reduce external API calls and costs (e.g., weather, currency exchange rates). | | **Session-specific data** | Improve user experience (e.g., shopping cart, user preferences). | ## Bad Candidates for Caching | Data Type | Why Not Cache? | | --- | --- | | **Rapidly changing data** | Cached values might become stale (e.g., stock prices, live scores). | | **Sensitive or personal data** | Security and privacy risks. | | **Data with strict consistency needs** | Can lead to stale reads (e.g., banking transactions). | #### 2. How Long Should Data Be Cached? **Cache duration depends on how frequently the data changes and how critical freshness is.** | Data Type | Suggested Cache Duration | | --- | --- | | **Static content** (logos, CSS, JS) | Days to weeks (`max-age=604800`) | | **Product lists, categories** | Hours to a day (`max-age=3600 to 86400`) | | **User sessions, shopping carts** | Session duration (`Sliding Expiration`) | | **News articles, blog posts** | Minutes to hours (`max-age=600 to 3600`) | | **Real-time stock prices, chat messages** | Do not cache (or use very short TTL < 10s) | ## Caching Strategies | Strategy | When to Use? | | --- | --- | | **Absolute Expiration** (`max-age`) | Good for data that updates at known intervals (e.g., daily reports). | | **Sliding Expiration** | Ideal for session-related data (e.g., extend expiry as long as the user is active). | | **ETag / Last-Modified** | Best for browser caching (ensure the latest data is fetched only if changed). | | **Cache Invalidation** | Use when data needs immediate updates (e.g., clear cache when an order is placed). | #### 3. Choosing Cache Location | Cache Type | Use Case | | --- | --- | | **MemoryCache** | Fastest, best for single-server apps. | | **Distributed Cache (Redis, SQL Server Cache)** | Best for multi-instance apps. | | **Browser Cache (Cache-Control, ETag)** | Best for static assets and API responses. | | **CDN (Content Delivery Network)** | Best for images, scripts, videos. | #### #### Summary 1. Cache frequently accessed, expensive, or static data. 2. Avoid caching real-time, sensitive, or fast-changing data. 3. Set cache duration based on data volatility (seconds for real-time, hours/days for static data). 4. Use a combination of in-memory, distributed, and browser caching for efficiency. 5. Implement cache invalidation strategies for dynamic content. ### ## Answers ### Answer by Anubhav Sharma #### How to Decide What Data to Cache and for How Long? Caching is a trade-off between **freshness** and **performance**. To decide what data to cache and for how long, consider the following factors: #### 1. What Data Should Be Cached? ## Good Candidates for Caching | Data Type | Reason for Caching | | --- | --- | | **Frequently accessed data** | Avoid redundant database or API calls (e.g., top articles, user profile). | | **Expensive computations** | Save CPU time (e.g., complex reports, aggregated statistics). | | **Static or rarely changing data** | No need to fetch frequently (e.g., product categories, country lists). | | **Third-party API responses** | Reduce external API calls and costs (e.g., weather, currency exchange rates). | | **Session-specific data** | Improve user experience (e.g., shopping cart, user preferences). | ## Bad Candidates for Caching | Data Type | Why Not Cache? | | --- | --- | | **Rapidly changing data** | Cached values might become stale (e.g., stock prices, live scores). | | **Sensitive or personal data** | Security and privacy risks. | | **Data with strict consistency needs** | Can lead to stale reads (e.g., banking transactions). | #### 2. How Long Should Data Be Cached? **Cache duration depends on how frequently the data changes and how critical freshness is.** | Data Type | Suggested Cache Duration | | --- | --- | | **Static content** (logos, CSS, JS) | Days to weeks (`max-age=604800`) | | **Product lists, categories** | Hours to a day (`max-age=3600 to 86400`) | | **User sessions, shopping carts** | Session duration (`Sliding Expiration`) | | **News articles, blog posts** | Minutes to hours (`max-age=600 to 3600`) | | **Real-time stock prices, chat messages** | Do not cache (or use very short TTL < 10s) | ## Caching Strategies | Strategy | When to Use? | | --- | --- | | **Absolute Expiration** (`max-age`) | Good for data that updates at known intervals (e.g., daily reports). | | **Sliding Expiration** | Ideal for session-related data (e.g., extend expiry as long as the user is active). | | **ETag / Last-Modified** | Best for browser caching (ensure the latest data is fetched only if changed). | | **Cache Invalidation** | Use when data needs immediate updates (e.g., clear cache when an order is placed). | #### 3. Choosing Cache Location | Cache Type | Use Case | | --- | --- | | **MemoryCache** | Fastest, best for single-server apps. | | **Distributed Cache (Redis, SQL Server Cache)** | Best for multi-instance apps. | | **Browser Cache (Cache-Control, ETag)** | Best for static assets and API responses. | | **CDN (Content Delivery Network)** | Best for images, scripts, videos. | #### #### Summary 1. Cache frequently accessed, expensive, or static data. 2. Avoid caching real-time, sensitive, or fast-changing data. 3. Set cache duration based on data volatility (seconds for real-time, hours/days for static data). 4. Use a combination of in-memory, distributed, and browser caching for efficiency. 5. Implement cache invalidation strategies for dynamic content. ### --- Original Source: https://www.mindstick.com/interview/34024/how-do-you-decide-what-data-should-be-cached-and-for-how-long Copyright © MindStick Software Pvt. Ltd. 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