A return to Postgres isolation

Over the years, I’ve participated in a few system design interviews. Some went my way and others didn’t. One thing has stayed consistent: when I’m designing an online system, transaction isolation almost always comes up in the discussion. When the requirements call for a CP system, I usually go for a PostgreSQL-compatible NewSQL database such as Aurora PostgreSQL, DSQL, or CockroachDB. Andy Pavlo and Matthew Aslett define NewSQL as relational databases that aim for NoSQL-like scale while keeping SQL and ACID transactions. Part of the reason is that I like thinking in Postgres. There’s also the usual interview move where a system starts at a modest scale and then the interviewer cranks it up by 100x for shits and giggles. With shared-nothing Postgres, I may suddenly need manual sharding or a different database. Either choice can change the transaction boundary and force a substantial redesign. NewSQL lets me keep the relational model and distributed transactions across a wider range of…