Write-Around Caching
Prevent cache pollution: Direct-to-database writes, lazy read population, and large blob ingestion patterns.
01.1. What is Write-Around Caching?
In the Write-Around Caching pattern, data is written directly to persistent storage (Primary Database, Object Store, or S3), completely bypassing the in-memory cache layer.
The data only enters the cache later if and when an application client explicitly reads it (lazy loading via Cache-Aside).
The Problem it Solves: Cache Pollution (Cache Churn)
Suppose an application executes a bulk data import (e.g., uploading 100,000 PDF invoices, streaming terabytes of video chunks, or generating archival monthly compliance reports):
- If the system used Write-Through or populated the cache on every write, this massive wave of cold data would flood into RAM.
- To make room for the new writes, the cache's LRU eviction algorithm would evict valuable, hot user profile data and active session tokens.
- Immediately afterward, normal user traffic would suffer a catastrophic wave of cache misses (cache pollution).
Write-Around protects the hot working set by ensuring that cold, infrequently read data never touches expensive cache memory upon creation.
Write-Around Workflow 🚫
Write-Around Workflow 🚫
Writes bypass the cache completely to avoid evicting hot data.
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