Google's Spanner paper was published in 2012 which famously introduced the TrueTime API. PTP is the standard equivalent of TrueTime. Two years later, Kulkarni, et al. published the Hybrid Logical Clock paper – Logical Physical Clocks and Consistent Snapshots in Globally Distributed Databases. In the HLC paper, they list the downsides…
Previous post can be found here – https://blog.the-pans.com/state-machine/. The entire series is based on Lamport's TLA+ tutorial. In the previous post, we talked about any system can be described as a state machine. What language should we use to describe state machines? TLA+ uses mathematics, which is…
I have wanted to read the paper, Spanner: becoming a SQL system from SIGMOD 2017 for a while and finally got a chance to finish reading it. I have mixed feelings. The paper mostly focuses on the DQL aspect of SQL and only briefly mentioned DML and locking. I like…
Linearizability is one of the strongest single-object consistency models, and implies that every operation appears to take place atomically, in some order, consistent with the real-time ordering of those operations (https://jepsen.io/consistency/models/linearizable). Quite often people make the mistake of over-simplifying linearizability as the ability of being…
I previously wrote a post on reasoning DNS as a distributed database. In the same spirit, today, let's take a look at IP as distributed data (the Internet would be a distributed database in this analogy). This is inspired by a very interesting blog post from Cloudflare, https://blog.cloudflare.…
This post is a slightly expanded version of my earlier tweet. In software systems, "betting" is actually a common practice. One of the most common bets people place is retry. When the first attempt doesn't work, we can just "try it again". Retry is a bet – you are betting on…
In this post, we will show that a generic distributed critical section can't satisfy both safety and liveness properties with even a single faulty client process. System Model We assume a non-real-time system with no bound on process time or network delay. In the system, there exists a lock service…
This is a very practical paper. It focuses on practical matters such as admission control, non-uniform access patterns, metastability introduced by caches, etc. You won't find fancy distributed system algorithms in this paper. But it's an important paper which covers critical topics nonetheless. A system only delivers real value to…