These days, every second counts when loading a webpage or an app. You want your websites to feel as snappy as possible, and for that, managing the load on your servers becomes a priority. Here, we use a technique that not only achieves load-reduction, but also ensures that resources are used wisely.
If you’ve ever wondered how websites handle multiple users asking for the same thing simultaneously, request collapsing is often the answer.
What is Request Collapsing?
Request collapsing is the practice of combining multiple identical requests into a single one. Imagine a popular website where thousands of users request the same resource, like a video or image.
Instead of processing thousands of duplicate requests, the system groups them together and sends only one request to the server. When the response comes back, it’s shared with all the users who asked for it.
By doing this, websites and servers avoid unnecessary processing and ensure faster delivery of content.
Why is Request Collapsing Important?
Without request collapsing, servers would become overwhelmed by handling duplicate requests. This could lead to:
- Increased server load: Processing identical requests wastes resources.
- Slower response times: Users experience delays as the server struggles to keep up.
- Potential crashes: High traffic volumes could overload servers entirely.
Request collapsing prevents these issues and ensures smoother operations, especially during peak traffic.
How Does Request Collapsing Work?
Request collapsing often relies on a cache to temporarily store the response to a request. Here’s a simplified example:
- User Request: Multiple users ask for the same data simultaneously.
- Check Cache: Before sending the request to the server, the system checks if the data is already in the cache.
- Collapse Requests: If the data isn’t in the cache, the system sends just one request to the server and marks others as “waiting.”
- Serve the Response: When the server responds, the data is stored in the cache and shared with all the waiting requests.
This process avoids sending duplicate requests and ensures that users get the response quickly.
How Request Collapsing Identifies Duplicate Requests
For request collapsing to work effectively, the system must recognize when two or more requests are asking for the exact same content. Here’s how it typically identifies duplicates:
- Unique Identifiers: Each requested resource is identified by a unique key, often derived from the URL or query parameters. For example, two users requesting example.com/image.jpg will have identical keys.
- Hashing: Systems may use hashing algorithms to generate a unique fingerprint for each request. This allows the system to quickly compare fingerprints and detect duplicates.
- Request Headers and Parameters: The system analyzes headers and parameters, ensuring that requests with identical metadata are grouped together. For instance, example.com/data?id=123 is treated as a separate request from example.com/data?id=456.
- Real-Time Lookup in Cache or Queue: Before sending a request to the server, the system checks if:
- The content is already in the cache (to serve immediately).
- Another request for the same resource is currently in progress (to group the new request with the ongoing one).
- Collapsing Time: The system sets a short time window, like 100 milliseconds, where all identical incoming requests are grouped. This helps capture requests that arrive almost simultaneously but slightly staggered.
Avoiding the Cache Stampede
While request collapsing is effective, it can sometimes lead to a cache stampede. This happens when multiple users request the same resource, but the cache doesn’t have the data yet.
If the system doesn’t manage collapsing properly, it might still send too many requests to the server, causing a bottleneck. For instance, if a page takes 3 seconds to render and receives 10 requests per second, the expiration of the cached page could lead to 30 simultaneous processes attempting to regenerate the same content. This surge can overwhelm servers and lead to system collapse.
To handle this, developers implement a waiting for cache mechanism. This ensures that once one request is made, all others wait until the data is cached. This way, the server isn’t flooded with duplicate requests.
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Request Collapsing vs. Request Coalescing
You might have heard of request coalescing, which is similar to request collapsing. However, the two have subtle differences:
While both aim to optimize resources, request collapsing focuses on reducing duplicate requests, whereas request coalescing often works to consolidate multiple smaller requests.
Benefits of Request Collapsing
Here’s why request collapsing is so valuable for modern web systems:
1. Reduces Server Load
Servers don’t need to process the same request multiple times. By collapsing identical requests, you significantly reduce the strain on your infrastructure.
For instance, instead of handling 1,000 separate requests for the same image, the server handles just one, freeing up resources for other tasks.
2. Improves Response Times
Fewer duplicate requests mean faster responses for users.
With request collapsing, the system spends less time queuing and processing redundant requests, ensuring that users get their data without delays.
This is especially important for high-traffic websites where every millisecond matters.
3. Prevents Overload During Peak Times
When websites experience sudden spikes in traffic—like during flash sales, ticket bookings, or live streams—servers can easily become overwhelmed.
Request collapsing ensures that these spikes are manageable by funneling duplicate requests into a single process, reducing the risk of downtime or crashes.
4. Enhances User Experience
Nobody likes waiting for a page to load. Request collapsing improves the overall speed and reliability of a website or application, leading to happier users.
Faster responses make users more likely to stay on your platform and return in the future.
5. Reduces Bandwidth Consumption
By sending fewer requests to the server and utilizing cached data, you also save on bandwidth.
This is particularly important for systems where bandwidth is a limiting factor or incurs additional costs.
Implementing Request Collapsing in Your System
Here’s how you can implement request collapsing effectively:
- Use a Cache
Start by setting up a caching system. A cache stores frequently accessed data temporarily, allowing the system to serve users without contacting the server repeatedly. Common solutions include Redis, Memcached, or in-browser caching. - Introduce a Collapsing Time Window
Define a short time frame, often called a collapsing time, where incoming identical requests are grouped together. For example, if multiple requests for the same resource arrive within 100 milliseconds, they can be collapsed into one. Fine-tuning this window ensures minimal delays while maximizing efficiency. - Handle Cache Misses Gracefully
When the requested data isn’t available in the cache, it’s crucial to ensure that only one request goes to the server while others wait. This prevents a cache stampede, where the server is flooded with duplicate requests during a cache miss. - Implement Request Queues
Use request queues to manage waiting requests. When the collapsed request is being processed, other incoming requests can wait in a queue, ready to be served as soon as the data becomes available.
Where is Request Collapsing Used?
Here are some real-world scenarios where request collapsing proves invaluable:
| Application | Description |
|---|---|
| Content Delivery Networks (CDNs) | CDNs handle massive amounts of traffic by caching resources like images, videos, and scripts close to users. Request collapsing ensures that popular assets are fetched from the server only once, reducing latency and improving delivery times. |
| E-commerce Websites | During events like Black Friday sales, thousands of users may view the same product page simultaneously. Request collapsing ensures that these identical requests don’t overload the server, maintaining a seamless shopping experience. |
| API Services | APIs providing frequently accessed data—like live weather updates, stock prices, or sports scores—benefit significantly from request collapsing. Instead of processing repetitive calls, the API serves cached responses to multiple users. |
| Social Media Platforms | Popular social media posts or trending content often receive millions of requests. Request collapsing ensures that these requests are managed efficiently without impacting the platform’s performance. |
