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Posted on Dec 17

How Do You Cache Partial Responses or Specific Elements in Apigee X?

#apigee #gcp #google #apigeex

A beginner-friendly guide to partial response caching in Apigee X with real-world scenarios and step-by-step examples

Learn how to implement partial response caching in Apigee X to improve API performance by caching specific elements instead of full responses.

Introduction

Imagine you’re building an API for an e-commerce application. Every time a user opens the product page, your backend recalculates product details, pricing, and user-specific offers. But here’s the catch: product details rarely change, while offers change frequently.

Wouldn’t it be wasteful to cache the entire response when only part of it is reusable?

This is where partial response caching in Apigee X becomes incredibly powerful.

In modern API management, performance and scalability are everything. Apigee X allows you to cache not just full API responses, but specific elements or fragments of a response. This approach reduces backend load, improves latency, and gives you fine-grained control over what should and shouldn’t be cached.

In this blog, you’ll learn:

What partial response caching means in Apigee X
When and why you should use it
A step-by-step beginner-friendly implementation
Best practices and common mistakes to avoid

Core Concepts

What Is Response Caching in Apigee X?

In Apigee X, API proxies sit between clients and backend services. One powerful feature of these proxies is response caching, which temporarily stores API responses so repeated requests can be served faster.

By default, caching is often thought of as “cache everything.” But real-world APIs aren’t that simple.

What Is Partial Response Caching?

Partial response caching means caching only a specific part of the response, instead of the full payload.

Think of it like a restaurant menu:

The menu items rarely change → cache them
The daily offers change often → don’t cache them

Instead of storing the whole menu every time, you store only the static parts and dynamically assemble the final response.

Why Cache Partial Responses?

Use cases and benefits:

Reduce backend calls for static data
Improve API response time
Avoid serving stale dynamic data
Optimize cache size and efficiency
Better control over API traffic management

This is especially useful in Apigee X when dealing with:

User profile APIs
Product catalogs
Configuration or reference data
Hybrid static + dynamic responses

Step-by-Step Guide: Partial Response Caching in Apigee X

Scenario

Backend response:

{
  "userId": "123",
  "name": "Ravi",
  "accountType": "PREMIUM",
  "balance": 8450.75,
  "lastLogin": "2025-12-15T10:30:00Z"
}

accountType → changes rarely ✅ cache it
balance and lastLogin → dynamic ❌ don’t cache

Step 1: Extract the Cacheable Element

Use an ExtractVariables policy to pull out the static part.

<ExtractVariables name="EV-Extract-AccountType">
    <JSONPayload>
        <Variable name="accountType">
            <JSONPath>$.accountType</JSONPath>
        </Variable>
    </JSONPayload>
</ExtractVariables>

📌 This extracts accountType into a flow variable.

Step 2: Cache the Partial Value

Use a ResponseCache policy to cache only the extracted element.

<ResponseCache name="RC-Cache-AccountType">
    <CacheKey>
        <KeyFragment ref="request.header.user-id"/>
    </CacheKey>
    <Scope>Exclusive</Scope>
    <ExpirySettings>
        <TimeoutInSec>3600</TimeoutInSec>
    </ExpirySettings>
    <Source>accountType</Source>
</ResponseCache>

📌 Only the accountType value is cached, not the full response.

Step 3: Populate Response Using Cached Data

Before sending the response back to the client, inject the cached value using AssignMessage.

<AssignMessage name="AM-Inject-Cached-Value">
    <AssignTo createNew="false" type="response"/>
    <Set>
        <Payload contentType="application/json">
            {
              "userId": "{request.header.user-id}",
              "accountType": "{accountType}",
              "balance": "{response.balance}",
              "lastLogin": "{response.lastLogin}"
            }
        </Payload>
    </Set>
</AssignMessage>

📌 This creates a hybrid response: part cached, part dynamic.

Flow Diagram (Conceptual)

Client
  |
  v
Apigee X API Proxy
  |
  |-- Check cache for accountType
  |
  |-- Call backend for dynamic data
  |
  |-- Merge cached + dynamic values
  |
  v
Final Response to Client

Best Practices

Cache only what is truly static
Avoid caching user-specific or frequently changing fields.
Design meaningful cache keys
Use identifiers like user ID, region, or product ID.
Set appropriate TTL values
Short TTLs for semi-static data, longer TTLs for reference data.
Avoid caching sensitive information
Never cache PII, tokens, or confidential data.
Monitor cache performance
Use Apigee analytics to track hit/miss ratios.

Common Mistakes to Avoid

❌ Caching the full response when only part is reusable
❌ Using the same cache key for different users
❌ Ignoring cache invalidation strategies
❌ Not testing cache behavior under load

Conclusion

Partial response caching in Apigee X is a powerful technique that gives you fine-grained control over performance optimization. Instead of blindly caching everything, you cache only what makes sense, resulting in faster APIs, reduced backend load, and happier consumers.

By combining ExtractVariables, ResponseCache, and AssignMessage policies, you can design intelligent API proxies that balance speed and freshness. This approach is especially valuable in real-world enterprise APIs where data changes at different rates.

Now that you understand the concept, try implementing partial response caching in one of your APIs and observe the performance gains firsthand.

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