PostgreSQL: VACUUM e MVCC
Referências
Artigo do Heroku
https://devcenter.heroku.com/articles/postgresql-concurrency
Artigo super interessante em um blog
http://blog.lerner.co.il/in-postgresql-as-in-life-dont-wait-too-long-to-commit/
Artigo super interessante
https://blog.sentry.io/2015/07/23/transaction-id-wraparound-in-postgres