Concurrency Corner

What is a rate limiter The Rate Limiter (RL) is a middleware (think Redis) or some software strategy to limit access of clients to resources that are limited or for which we want to ensure that fair usage and access is encouraged. In the context of websites the approach also provides security as it limits access to adversarial clients who wish to abuse the system. This approach also finds use in the context of databases - which I will give details on in this post. Note: adversaries are a superset of the user set (they can do what users do plus other things we dont normally want to allow) who behave badly, and could be external actors to the system or registered members. Rate Limiters in Distributed Systems The poster child for rate limiting - in my opinion - is Redis as it is the first thing that comes to mind from my background and experience. The reason is that they have made the use of rate limiting simple via their api. You should check out Redis if you have not alre...

The present post is about Caches and the Buffer Pool Manager for a database named SparrowDB that I am building. The programming language is Rust. The DB is a SQL relational database I wish to take from scratch to distributed. If you wish to come along for the ride, I will post weekly on my thoughts, struggles and completed work. Disclaimer: A lot of what I know and some parts of this blog comes from lessons by Andy Pavlo from CMU who made a youtube course, and I highly recommend you learn from him if you desire to work with database internals. Cache Policies : There are several types of caches we could consider eg. course-grained and fine-grained, but we will only consider the former category. Furthermore we will only use LRU-K in this project, but I wish to give an honourable mention to frequency based cache policies such as Q2 and LFU. The LRU-K is an improvement on the LRU policy as it avoids thrashing in the database cache where we evict a page only to read it again in t...