Caching Redis & Internal

What is caching?

A cache is a hardware or software component that stores data so that future requests for that data can be served faster. The data stored in a cache might be the result of an earlier computation or a copy of data stored elsewhere. In mentoring services, all the necessary data which are used frequently will be cached in Redis and the Internal cache.

What is hit and miss in caching?

A cache miss occurs when a cache does not have the requested data in its memory. Meanwhile, a hit is when a cache successfully finds the requested data, satisfying the search query.

How Caching is implemented in Elevate services?

Caching Implementation

Internal and Redis caching is implemented with the help of an npm package called elevate-node-cache. This package exports 3 modules.

1. RedisConfig
2. RedisCache
3. InternalCache

Module	Description
RedisConfig	This module has one function which needs to be called at the start of the microservice. To initialize the global Redis client, pass the Redis URL to this function as a parameter.
RedisCache	This module has three functions for caching - set, delete and read cache from memory. You need to pass Key in the read and delete functions to get cached data. In a set function, you need to pass two mandatory parameters, namely Key and Value. A third optional parameter is time, which specifies how long the data needs to be cached. If the time parameter is not specified, the cache will be stored for forever. When the memory is full, the Redis eviction policy is used to clear memory. Expiry time must be in seconds.
InternalCache	This module has four functions for caching and initialization. * init function: Call this function at the start of an application and pass the Expiry time for the cache. * Set: Pass a Key and Value to set the cache. The function will use the default time, which is initialized at the start of an application.* Read: Pass the Key of cache to read the cache.* Delete: Pass the Key of cache to delete the cache.In the internal cache, you cannot modify the expiry time of a cache as it will get initialized at the start of an application. To change the expiry time of the cache, you need to update in env “INTERNAL_CACHE_EXP_TIME”. Expiry time must be specified in seconds.

In Elevate services, caching is implemented in 3 features

1. Form version cache (Internal cache)
2. Entity (Internal cache)
3. Mentor Profile (Redis)

Form version cache

In Elevate services, form services are consumed by the front-end application. Each form has a version and this version will be updated once the form is updated.

The front-end application will use a cache to store form data along with its version. If the form gets updated, its version will change and an API request will be sent to backend services for the latest data. The application’s limited and frequently used data will be stored in the internal cache to serve the application faster and better.

Form data will be saved in the below format.

           {
               "_id": "62e8bb2665320be5417a19e1",
               "type": "profile",
               "__v": 12
           },
           {
               "_id": "632844eb1b95f4e72732ab42",
               "type": "session",
               "__v": 5
           },
] ```
This data will be part of the meta key in responses. Data is not updated individually when any form gets updated then it will delete the formVersion key and the new query will create cache data in the formVersion key. While creating the cache value is converted into string format using Stringify and in retrieval, it will be parsed to JSON.