Akash's Blog

Introduction

Idea of cahing is to store frequently used data in high speed temporary storage to reduce load on database and improve overall performance.

Caching helps to reduce work of underlying database drasticaly, when we write and read something from database it is being read from the disk. To avoid frequent read from disk which are slower compared to reading it from primary memory.

Thus caching helps to load frequently used data in memory and use it when requested instead of looking into disk, makes things way faster and the overall latency and throughput impoves.

Latency is time taken to finish task.
Throughput is number of tasks finished in given time.

If you take 1 minute to read a page. Your latency is 1 minute and throughput is 60 PPH (Pages per hour).

Aspects of Caching

Caching can be done in many layers; client side, server side or at dedicated (separate) cache layer.

There are options available for cahing in following layers,

Database
Web server
Applciation server
Browser (or Client Side)
Distributed Caching
CDN (Content Delivery Network)

We need to consider different aspects while choosing the right caching mechanism. For example, quantity of data to be loaded, which data to put, refresh frequency of the data, expiry of the unused data (eviction), our cache should not face cold start or celebrity problem (if distributed) etc.

Following are different strategies which we can use to update (refresh) the data stored in cache. Image clarifies what is the placement of cache and closely looking at arrow gives idea of data flow.

Cache Aside
Write Through
Write Behind
Refresh Ahead

Also, cache should be evicted if not used for certain period of time for optimal storage use. One of the following eviction Strategies can be used.

LRU (Least Recently Used)
LFU (Least Frequently Used)
FIFO (First In First Out)

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Tuesday, March 11, 2025

System Design Series: Caching

Introduction

Aspects of Caching