Write-through caching

As explained in Learn Concurrent Programming with Go

Cache write-through is a cache update policy that immediately mirrors writes to the corresponding location in main memory.

Write-through caching mirrors a cache update to main memory immediately. It keeps memory current when one thread changes a shared variable, but other CPU caches may still hold stale copies. section 3.1

A shared-memory update can proceed as follows:

• Thread 1 updates its cached copy of a variable. section 3.1
• The update is mirrored to main memory, preventing a direct memory read from returning the older value. section 3.1
• Other caches listen for bus update messages and either apply the update or invalidate their affected cache line. section 3.1

Figure 3.4 Updating shared variables in an architecture with caches

Follow the shared-variable update across caches and memory. section 3.1

How Learn Concurrent Programming with Go covers it

How deep it goes

Describes the update sequence and its stale-cache limitation, then connects the remedy to cache-coherency protocols.

Examples

Uses two threads updating and reading one shared variable across processor caches, supported by an architecture figure.

What it assumes

Assumes shared variables, processor caches, main memory, and bus communication across multiple CPUs.

What you can do after

Evaluate why mirroring writes to memory does not alone prevent stale values in other processor caches.

How it connects

Connects cache write-through with main memory, local CPU caches, cache invalidation, and cache-coherency protocols.

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Also explained in

• 

  liveBookmanning.com
  Amazon Web Services in Action, Third Edition: An in-depth guide to AWSWrite-through caching is a caching technique that writes updated data synchronously to both the cache and the primary data store.
• 

  liveBookmanning.com
  Advanced Algorithms and Data StructuresWrite-ahead caching writes data to a cache before writing it to the underlying storage system.

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Related concepts

• write-behind cachingcontrasts with · Write-behind caching is a technique that records updates in a cache, acknowledges them, and later propagates them to a backing store.
• cachinguses · Caching is the practice of storing reusable data or computation results so later access can avoid repeating retrieval or computation.
• databaseuses · A database is an organized collection of persistent data managed by software for storage, retrieval, querying, and modification.
• memoryuses · Memory is a storage resource or mechanism that retains data or computational state for access during computation or later use.
• ACIDuses · ACID is the set of database transaction properties—atomicity, consistency, isolation, and durability—that characterize reliable transactional behavior.
• cache-aside cachingcontrasts with · Cache-aside caching is a pattern in which an application reads from a cache first, retrieves misses from backing storage, and populates the cache.

This explainer was generated by Manning's knowledge graph from the text of Learn Concurrent Programming with Go. The section links point to the parts of the book it draws on.