Singleflight

Answer-first: Effective caching strategy selection hinges on the acceptable consistency window and the read/write access pattern of the workload. Write-Through suits financial records; Write-Behind suits analytics and event counters; Cache-Aside is the default for read-heavy API responses. Prerequisite: Part 3 of the System Design Masterclass. Read Part 2: Load Balancing L4/L7 to understand the traffic layer before diving into the caching tier. What You’ll Learn That AI Won’t Tell You XFetch Mathematical Constants: How to configure the scaling factor ($\beta$) in XFetch to balance background refresh CPU usage against cache miss rates. Redis Memory Allocation Overhead: How Redis’s internal jemalloc allocator causes memory fragmentation, and why LRU evictions don’t immediately free up RAM. Singleflight Leakage: The danger of singleflight lockups when backend queries hang indefinitely, and how to guard it using Go context timeouts. How Does Cache Stampede Happen? Key Concept: Cache Stampede (thundering herd) occurs when a popular cached key expires and multiple concurrent goroutines simultaneously detect a cache miss — then all query the database simultaneously. The burst of duplicate DB queries can exceed connection pool capacity and cause cascading failure. ...

Prerequisite: Before reading this chapter, please ensure you have read the previous article in this series: Chapter 1: How Systems Handle Millions of Requests/s (C10M)? Lessons from Shopee & Alipay. Caching is the ultimate shield for databases in distributed systems. However, poorly implemented caches can become the exact reason your system crashes. In this chapter, we dissect three classic caching phenomenons and how to defend against them using Golang. 1. Cache Penetration & Bloom Filter Mathematics Cache penetration occurs when attackers query non-existent IDs, bypassing the cache entirely. Defend against it by caching NULL values or utilizing Bloom Filters at the memory level. ...