Cache Strategies

tl;dr

The diagram below illustrates how those 5 strategies work. Some of the caching strategies can be used together.

Read strategies

Read Cache Aside

The cache sits on the side, and the application directly talks to both the cache and the database.

There is no connection between the cache and the primary database. All operations to cache and the database are handled by the application.

Advantages

• Cache-aside caches are usually general purpose and work best for read-heavy workloads
• The read aside cache method can lead to faster performance and reduced response times as data is retrieved from the cache instead of the database or storage.
• It can result in reduced resource usage on the database or storage system.

Disadvantages

• Systems using cache-aside are resilient to cache failures. If the cache cluster goes down, the system can still operate by going directly to the database. (Although, it doesn’t help much if cache goes down during peak load. Response times can become terrible and in worst case, the database can stop working.)

When cache-aside is used, the most common write strategy is to write data to the database directly. When this happens, cache may become inconsistent with the database To deal with this, developers generally use time to live (TTL) and continue serving stale data until TTL expires. If data freshness must be guaranteed, developers either invalidate the cache entry or use an appropriate write strategy

Read Through

Read-through caches work best for write-heavy workloads workloads

Read-through cache sits in-line with the database.

When there is a cache miss, it loads missing data from database, populates the cache and returns it to the application.

Advantage

• logic for read-throw is usually supported by the library or stand-alone cache provider.
• The read-throw method ensures that the data being used is always up-to-date and accurate

Disadvantages

• when the data is requested the first time, it always miss cache and incurs the extra penalty of loading data to the cache.
• It can result in increased resource usage on the database or storage system.

Write strategies

Write Through

write-through caches work best for write-heavy workloads workloads

Data will write to the cache first and the cache immediately writes to the database

when recipt a data The data will be cached

Cache will send a request to save data to the database immediately.

Advantages

• There is never a cache miss, because data is always cached before being saved to the database.
• There is no case where the data does not match the database
• The data is always identical if we combine Write through cache and Read through cache.

Disadvantages

• The process of saving data will often take a extra time because it has to wait for the cache and database to be saved
• Most of the data on the cache is read-once data, so writing to the cache will result in a lot of unnecessary data remaining on the cache => unnecessary resource consumption

Write Back

Cache will synchronize data to the database periodically over time, or according to the amount of data inserted / updated.

Advantages

• Reduce the writing pressure on the database, thereby reducing costs and problems related to the database
• If we combine Write back and Read through cache, we have a good system for both read heavy workloads and write heavy workloads.

Disadvantages

• Data may not be consistent between the cache and the database if the cache has not synchronized the data to the database.
• If the cache is dead, the system will be dead, we may lose forever data that the cache has not synchronized to the database.

Write Around

This strategy is only suitable for data that rarely changes and the system accepts the delay of data, because data may not be consistent in the cache when the cache has not expired (expired) but has new data updated.

Advantages This strategy when there is data to change, will only be recorded in dB and skip the cache.

This will be able to reduce the cache that is flooded with record operations that it is likely that these data will never be used.

Disadvantages It is very easy to cause the case of "cache miss" if the client sends a new request from a new record, it will cause a delay when reading because the data must be read from the dB, then it is recorded in the cache and returns to the client.