Why we spent the last month eliminating PostgreSQL subtransactions
Definitely a fun article.This was the key takeaway for me.    SubtransControlLock indicates that the query is waiting for PostgreSQL to load subtransaction data from disk into shared memory.

I felt the article fell down for two reasons:
(1) It didn't really articulate the need for transactions in the first place (database integrity). Nor did it discuss the implications on integrity with this change.(2) It didn't articulate the possibilities of other architectures (pushing to a read cache other than PostgresSQL like Cassandra).I got the feeling they were really pushing PostgresSQL to its limits in their cluster with their load - and it was time to consider another design.