First-In-First-Out(FIFO)

First-In-First-Out (FIFO) is a cache eviction policy that removes the oldest item from the cache when it becomes full. In this strategy, data is stored in the cache in the order it arrives, and the item that has been present in the cache for the longest time is the first to be evicted when the cache reaches its capacity.

For Example:

Imagine a cache with a capacity of three items:

1. A is added to the cache.
2. B is added to the cache.
3. C is added to the cache.

At this point, the cache is full (capacity = 3)

If a new item, D, needs to be added, the FIFO policy would dictate that the oldest item, A, should be evicted. The cache would then look like:

• D is added to the cache (A is evicted).
• The order of items in the cache now is B, C, and D, reflecting the chronological order of their arrival.
• This ensures a fair and straightforward approach based on the sequence of data access, making it suitable for scenarios where maintaining a temporal order is important.

Advantages of First-In-First-Out(FIFO)

1. Simple Implementation: FIFO is straightforward to implement, making it an easy choice for scenarios where simplicity is a priority.
2. Predictable Behavior: The eviction process in FIFO is predictable and follows a strict order based on the time of entry into the cache. This predictability can be advantageous in certain applications.
3. Memory Efficiency: FIFO has relatively low memory overhead compared to some other eviction policies since it doesn’t require additional tracking of access frequencies or timestamps.

Disadvantages of First-In-First-Out(FIFO)

1. Lack of Adaptability: FIFO may not adapt well to varying access patterns. It strictly adheres to the order of entry, which might not reflect the actual importance or relevance of items.
2. Inefficiency in Handling Variable Importance: FIFO might lead to inefficiencies when newer items are more relevant or frequently accessed than older ones. This can result in suboptimal cache performance.
3. Cold Start Issues: When a cache is initially populated or after a cache flush, FIFO may not perform optimally, as it tends to keep items in the cache based solely on their entry time, without considering their actual usage.

Use Cases of First-In-First-Out(FIFO)

• Task Scheduling in Operating Systems: In task scheduling, FIFO can be employed to determine the order in which processes or tasks are executed. The first task that arrives in the queue is the first one to be processed.
• Message Queues: In message queuing systems, FIFO ensures that messages are processed in the order they are received. This is crucial for maintaining the sequence of operations in applications relying on message-based communication.
• Cache for Streaming Applications: FIFO can be suitable for certain streaming applications where maintaining the order of data is essential. For example, in a video streaming cache, FIFO ensures that frames are presented in the correct sequence.

Cache eviction refers to the process of removing data from a cache to make room for new or more relevant information. Caches store frequently accessed data for quicker retrieval, improving overall system performance. However, caches have limited capacity, and when the cache is full, the system must decide which data to remove. The eviction policy determines the criteria for selecting the data to be replaced. This post will dive deep into Cache Eviction and its policies.