Cache_Aside.md

Cache-Aside

• Motivation
• Solution
  • Concepts
  • Implementation
• Pros & Cons
  • Pros
  • Cons
• Consideration
• When To Use
• References

Motivation

• Some caching systems don't provide read-through and write-through/write-behind operations.

Solution

Concepts

• Applications take the responsibility of using the cache to maintain data.
• The cache does not interact with database directly.

Implementation

Read Operation

• Check the requested record is held in the cache or not:
  • If the requested record is held in the cache:
    • Return the record directly.
  • If the requested record is not in the cache:
    • Read the record from the database and return it.
    • Store the copy of the record in the cache.

Write Operation

• Write the record into the database.
• Invalidate the corresponding record in the cache.

Pros & Cons

Pros

• Improve performance on read operations generally.

Cons

• Cost more efforts on development (Applications need to handle both cache and database).
• Data in the cache can become stale if it is updated in the database.
• Each cache miss causes a noticeable delay (Data need to load from database to cache through application).

Consideration

Topic	Consideration	Possible Solution Options

When To Use

• The cache doesn't provide read-through and write-through/write-behind operations.
• The application performs more read operations than write operations.

References

• Web Article: Cache-Aside pattern | https://docs.microsoft.com/en-us/azure/architecture/patterns/cache-aside
• Web Article: [缓存更新的套路 | https://coolshell.cn/articles/17416.html)