Each transaction isolation level specifies what can or cannot happen when two queries are being run in parallel, i.e.: the memory semantics of the system.
Remember that queries can affects thousands of rows, and database systems like PostgreSQL can run multiple such queries at the same time.
Good summary on the PostgreSQL page: https://www.postgresql.org/docs/14/transaction-iso.html
- Nodejs/sequelize/raw/parallel_select_and_update.js | 488, 524, 1
- Isolation | 38
- Memory semantics | 59, 63, 1
- SELECT FOR UPDATE | 47