Notes about Cutting-Edge Technologies and Everything

After many years of Big Data, NoSQL, and Schema-on-Read detours, there is a clear return to SQL as the lingua franca for data operations. Developers need the comprehensive expressiveness that SQL provides. A world without SQL ignores more than 40 years of database research and results in hard-coded spaghetti code in applications to handle functionality that SQL handles extremely efficiently such as joins, groupings, aggregations, and (most importantly) rollback when updates go wrong. Luckily, there is a modern architecture for SQL called Distributed SQL that no longer suffers from the challenges of traditional SQL systems (cost, scalability, performance, elasticity, and schema flexibility). The key attribute of Distributed SQL is that data is stored across many distributed storage locations and computation takes place across a cluster of networked servers. This yields unprecedented performance and scalability because it distributes work on each worker node in the cluster in parall...

Concurrency bugs caused by weak transaction isolation are not just a theoretical problem. They may cause customer data to be corrupted. Many popular relational databases, which are usually considered ACID use weak isolation, so they would not necessarily have prevented these bugs from occurring. What exactly the Isolation guarantee in the SQL standard means based on what they call “read phenomena”. There are three types of phenomena: Dirty reads – If another transaction writes, but does not commit, during your transaction, is it possible that you will see their data? Non-repeatable reads – If you read the same row twice, is it possible that you might get different data the second time? Phantom reads – If you read a collection of rows twice, is it possible that different rows will be returned the second time? In the SQL standard, there are four levels of transactional isolation based on which of these phenomena they prevent (from weakest to strongest): Read Uncommitted – A tra...

Interesting article about Datomic and its immutability with regard to MVCC databases. https://www.xaprb.com/blog/2013/12/28/immutability-mvcc-and-garbage-collection/